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Circadian Rhythm

Episodes

sleep

Posted on September 17th 2025 (5 days)

Dr. Michael Grandner and Dr. Rhonda Patrick explore treatments for insomnia, detecting hidden sleep apnea, and science-backed strategies for better sleep.

circadian rhythm

"Doing This for 5 Minutes Every Morning Improves Mood, Sleep, & Alertness" - Andrew Huberman

Posted on September 27th 2024 (12 months)

In this clip, Dr. Andrew Huberman discusses the benefits of morning sunlight for sleep, timing, alternatives, and managing light exposure to optimize health.

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Q&A #46 with Dr. Rhonda Patrick (4/1/2023)

Posted on April 1st 2023 (over 2 years)

Dr. Rhonda Patrick answers audience questions on various health, nutrition, and science topics in this Q&A session.

Topic Pages

  • Breast milk and breastfeeding

    Maternal circadian rhythm drives temporal variations in breast milk melatonin, cortisol, and nutrients transferred during breastfeeding, shaping infant physiology.

  • Depression

    Circadian rhythm disruption alters CLOCK-gene expression, melatonin secretion and HPA-axis cortisol rhythms, precipitating and perpetuating depressive pathophysiology.

  • Fasting

    Fasting shifts circadian phase by activating AMPK and SIRT1, reprogramming peripheral clock gene oscillations independent of photic cues.

  • Melatonin

    SCN circadian signals induce nighttime pineal melatonin synthesis, and melatonin receptor activation feedback-entrains SCN neuronal oscillations.

  • NAD+

    CLOCK-BMAL1 induces NAMPT, generating rhythmic NAD⁺ that activates SIRT1, which deacetylates PER proteins to stabilize circadian oscillations.

  • Sirtuins

    SIRT1 senses NAD⁺ oscillations and deacetylates CLOCK–BMAL1 and PER2, thereby modulating transcriptional feedback loops governing circadian rhythms.

  • Sleep Regularity

    The suprachiasmatic nucleus synchronizes sleep timing, and regular sleep schedules reciprocally reinforce circadian phase stability.

  • Time-restricted eating

    Time-restricted feeding entrains peripheral clock gene oscillations, synchronizing metabolic pathways with central circadian pacemaker-derived hormonal cues.

News & Publications

  • Long-term exposure to bright, artificial night light linked to increased risk of overweight and obesity in schoolchildren. doi.org
    Circadian Rhythm Cortisol Development Melatonin Obesity Weight Loss

    Childhood obesity is a growing concern with multiple contributing factors, and perhaps, exposure to artificial light at night is among the most important. To investigate this, researchers in China followed more than 218,000 schoolchildren over a 15-year period.

    Each year, the students underwent health examinations that included body mass index measurements. At the same time, satellite data provided yearly measurements of how bright the outdoor night sky was in the area around each school. Children were then grouped based on long-term trends over the study period: areas that stayed consistently bright, areas that brightened slowly, areas that brightened rapidly, and areas where brightness declined. Because the rapidly brightening pattern had the lowest baseline light, it served as the reference group for all comparisons.

    The study revealed distinct differences across the light exposure groups:

    • Children attending schools in areas that stayed consistently bright had the highest risk. Boys had a 67% higher rate of becoming overweight or obese, and girls had a 56% higher rate.
    • In areas that brightened slowly, the risk was elevated but not statistically significant.
    • Areas where brightness declined showed no meaningful difference from the reference.
    • Among children who began at a normal or low weight, the consistently bright group recorded 9.95 new cases of overweight or obesity per 1,000 person-years, compared with 6.10 in the rapidly brightening group and 8.04 in the slowly brightening group.
    • On a population level, long-term exposure to consistently bright night-time environments accounted for about 40 percent of the risk in boys and 36 percent in girls.

    Prolonged exposure to artificial light disrupts circadian rhythms, the internal clocks that regulate daily cycles of hormones such as melatonin and cortisol. When these rhythms are disturbed, appetite, metabolism, and fat storage can be affected in ways that promote weight gain. Another possible mechanism may involve brown fat, a tissue that normally burns energy to generate heat but may become less active under constant night-time light. The differences between boys and girls may reflect a mix of biological sensitivity and behavioral factors such as screen use. Finally, the stronger risks in the consistently bright and slowly brightening groups may point to the impact of longer cumulative exposure, whereas more recent increases in brightness, as in the rapidly brightening group, may not have had the same effect.

    Conclusion:
    Children who attended schools in brighter night-time environments were more likely to gain excess weight over the school years. The study was limited because light levels were estimated from school locations, not individual homes, and detailed information on diet, activity, or puberty was unavailable. Moreover, while the analysis adjusted for broad regional differences, it cannot be ruled out that environmental and socioeconomic changes occurring alongside rising night-time light influenced the results. Still, the findings highlight night-time light as a potential and under-recognized factor in childhood overweight and obesity. Learn more about how to improve sleep in episode #45 featuring Dr. Matthew Walker.

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  • Regular cannabis use during adolescence may be linked to long-term insomnia risk. doi.org
    Development Drug Sleep Circadian Rhythm

    Adolescence is a critical window for brain development, and choices made during this time can shape long-term health. A twin study examined whether beginning regular cannabis use during the teenage years is connected to sleep problems in young adulthood.

    Researchers examined 1,882 twins with an average age of 23, and grouped them by cannabis use history: early regular users who started at 17 or younger, later regular users who started after 17, and never-regular users. Sleep outcomes included clinically defined insomnia and a more severe pattern combining insomnia with short weekday sleep (under six hours). By comparing identical twins, who share nearly all their genes, with fraternal twins, who share about half, the team could estimate how much of the link between cannabis use and sleep was due to genetic influences.

    Key findings from the study:

    • About 29 percent of early users reported insomnia, compared with 21 percent of later users and 19 percent of never-users. For the more severe type of insomnia, the rates were 9.9 percent in early users, 7.9 percent in later users, and 5.5 percent in never-users.
    • Early regular users were more likely to report both forms of insomnia, even after taking mental health and other factors into account.
    • Both the age at cannabis use onset and insomnia outcomes were strongly shaped by inherited factors. The same genetic influences contributed to both traits, indicating shared genetic liability rather than environmental overlap.

    Several pathways could link early cannabis use with later insomnia. One involves circadian and genetic factors, as cannabis may interact with the biological clock systems and genes that regulate circadian timing. Another concerns neurodevelopmental effects: during adolescence, brain regions involved in regulating arousal and sleep-wake patterns are still maturing, and exposure to cannabis may interfere with their normal neurodevelopment. Lastly, cannabis acts directly on the endocannabinoid system, which plays a role in both sleep and circadian regulation.

    Conclusion:

    The results suggest that starting cannabis use before age 18 is linked to a higher likelihood of insomnia in young adulthood. There was substantial genetic influence on cannabis use, sleep problems, and their association. Because adolescence is a sensitive period, early cannabis exposure could heighten long-term insomnia risk by disrupting ongoing brain and biological development. Since the study relied on self-reports, retrospective cannabis histories, and lacked information on other substances at the time sleep was measured, more prospective research is needed to clarify the long-term effects. Learn more about how cannabis, alcohol, and other factors affect sleep in this clip featuring Dr. Matthew Walker.

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  • Consistency in daily activity rhythms can enhance cardiorespiratory fitness and walking efficiency up to 20% in older adults. pubmed.ncbi.nlm.nih.gov
    Aging Circadian Rhythm Exercise

    A consistent daily schedule may do more than support sleep—it could also help maintain physical fitness as we age. Robust evidence suggests that disruptions in circadian rhythms, such as those caused by shift work or jet lag, are linked to poorer health outcomes. A recent study found that older adults with more regular daily activity patterns had better cardiorespiratory fitness and walked more efficiently than those with inconsistent routines.

    Researchers analyzed data from nearly 800 older adults (average age 76) who wore wrist devices that continuously monitored their movement. They measured how active each person was during the day compared to nighttime rest, identified the time of day when each person was most active, and determined the consistency of these patterns from day to day. The researchers then examined how activity rhythms were related to peak oxygen uptake (a measure of cardiorespiratory fitness) and the energy required to walk at different speeds, while accounting for factors such as age, sex, race, height, and chronic health conditions.

    Older adults who showed the greatest difference between daytime activity and nighttime rest had up to 20% better cardiorespiratory fitness and increased walking efficiency. Earlier times of peak activity were also associated with improved outcomes. Additionally, those who reached their peak activity at the same time each day tended to perform more effectively. These patterns encompassed all types of daily movement—including walking, cleaning, gardening, and shopping—not just formal exercise.

    These findings suggest that consistent, rhythmic activity patterns play a crucial role in maintaining physical function and health as we age. Learn more about developing an early circadian pattern in this clip featuring Dr. Satchin Panda.

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  • Working night shifts and accumulating sleep debt increase nurses' susceptibility to illnesses, with risk escalating by nearly 50% for frequent night shift workers. www.tandfonline.com
    Sleep Immune System Circadian Rhythm

    Shift work keeps essential services operating, but often at a cost to workers' health. Nurses, who frequently work irregular hours, may be particularly susceptible to disrupted sleep and weakened immune function. A recent study found that sleep debt and night shift work may elevate nurses' risk of common infections by as much as 50%.

    Researchers analyzed data from more than 1,300 nurses (average age, 42 years). Participants reported their typical sleep duration, how much sleep they needed, whether they worked night shifts, and how often they experienced infections, such as colds, pneumonia, sinusitis, or gastrointestinal infections, over the previous three months. The researchers used statistical methods to examine links between sleep patterns, shift schedules, and infection risk while accounting for age, sex, and whether the nurses had children at home.

    Nurses with greater sleep debt faced a higher risk of multiple infections. Those who slept one to two hours less than necessary were about 30% more likely to experience a cold, while those with more than two hours of sleep debt had more than double the risk. The risk of pneumonia, bronchitis, sinusitis, and gastrointestinal infections also rose with greater sleep debt. Working night shifts was linked to a 28% higher risk of experiencing a cold, and those with more frequent night shifts were nearly 50% more likely to report having a cold.

    These findings suggest chronic sleep debt and night shift work compromise the immune system, making nurses more susceptible to infections. Learn about practical ways to manage the risks of shift work in this episode featuring Dr. Satchin Panda.

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  • Melatonin supplementation may heighten DNA repair in night shift workers during daytime sleep, potentially reducing cancer risk. oem.bmj.com
    Cancer Sleep DNA Damage Circadian Rhythm Melatonin Supplements

    Working night shifts may increase the risk of cancer by disrupting the production of melatonin, a hormone essential for DNA repair. This disruption can impair the body’s ability to repair oxidative DNA damage, potentially contributing to cancer development. A recent study found that melatonin supplementation could improve the repair of oxidative DNA damage in night shift workers.

    The researchers conducted a four-week randomized, placebo-controlled trial with 40 night shift workers, providing them a 3-milligram dose of melatonin before their daytime sleep periods. They collected urine samples during daytime sleep and nighttime work periods, measuring 8-hydroxy-2′-deoxyguanosine (8-OH-dG), a marker of DNA repair capacity.

    They found that melatonin supplementation nearly doubled 8-OH-dG excretion during daytime sleep, indicating improved DNA repair. However, they observed no difference in 8-OH-dG excretion during the night shift. Although the melatonin group experienced a slight decrease in wakefulness after falling asleep, the researchers found no differences in total sleep duration or sleepiness levels between the two groups.

    The findings from this small study suggest that melatonin supplementation enhances oxidative DNA repair in night shift workers, offering the potential for reducing cancer risk. More extensive studies may identify optimal dosages and the long-term effects of melatonin supplementation in this population. Learn about the pros and cons of melatonin supplementation in this clip featuring Dr. Satchin Panda.

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  • Workplace design plays a crucial role in sleep health, with sedentary jobs and nontraditional schedules leading to poor sleep patterns, such as regular insomnia or compensatory 'catch-up' sleep. psycnet.apa.org
    Sleep Circadian Rhythm

    Modern workplace changes driven by technology are transforming not only how we work but also how well we sleep. Longer hours spent at desks, increasing reliance on computers, and nontraditional work schedules may undermine sleep health. A recent study found that modern job designs are linked to distinct sleep challenges among full-time workers.

    Researchers analyzed data from nearly 1,300 adults in the Midlife in the United States study, collected at two points over a decade. They examined six sleep health dimensions, including duration, insomnia symptoms, and daytime tiredness. Then, they identified three sleep health profiles: good sleepers (who had few sleep issues), catch-up sleepers (who relied on naps and non-workday sleep to offset shorter workday sleep), and insomnia sleepers (who experienced short sleep, frequent insomnia symptoms, and daytime tiredness).

    They found that only about half of the participants were good sleepers. Participants with sedentary jobs were more likely to be classified as insomnia sleepers. At the same time, those with nontraditional schedules often exhibited a catch-up sleeper pattern characterized by irregular sleep and regular napping. Good sleepers were less likely to be in these roles, suggesting that workplace design powerfully shapes long-term sleep health.

    These findings suggest that job design has marked effects on sleep quality. Reducing sedentary time and stabilizing work schedules could help workers achieve healthier sleep patterns, ultimately improving well-being and overall health. Learn how shift work and other aspects of modern lifestyles influence sleep and health by altering circadian rhythms in this clip featuring Dr. Satchin Panda.

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  • Moderate to high nighttime light exposure increases type 2 diabetes risk by up to 53 percent, comparable to genetic factors. t.co
    Metabolism Diabetes Circadian Rhythm Insulin Blue Light

    Circadian rhythms regulate metabolic processes, including glucose metabolism and insulin sensitivity. Disruptions in circadian rhythms can lead to metabolic impairments, increasing the risk of obesity, type 2 diabetes, and metabolic syndrome. A recent study found that personal light exposure patterns predict the risk of developing type 2 diabetes.

    Researchers assessed the light exposure patterns of more than 84,000 UK Biobank participants. Participants wore light sensors for one week to record their day and night light exposure. The researchers tracked the incidence of type 2 diabetes among the participants over an average follow-up period of nearly eight years.

    They found that diabetes risk increased as night light exposure increased. Compared to low light exposure, the risk of diabetes increased by - 29 percent with moderate light exposure. - 39 percent with high-moderate light exposure. - 53 percent with high light exposure. The increased risk associated with night light exposure was comparable to the difference between people with low and moderate genetic risk for diabetes.

    These findings suggest that nighttime light exposure is a risk factor for developing type 2 diabetes, comparable to genetic risk factors. Interestingly, low solar angle light – as in the early morning or late evening – resets the body’s circadian rhythms, improving metabolic health and mood. Learn more about low solar angle light exposure in this episode featuring Dr. Andrew Huberman.

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  • Gardening improves sleep quality better than other exercises, with sleep problems decreasing as the duration of gardening increases. www.psypost.org
    Exercise Sleep Circadian Rhythm Red Light Therapy

    Gardening is a popular pastime for many people, especially older adults, who benefit from the increased physical activity and mental engagement. A recent study found that people who garden sleep better than those who engage in other exercises or don’t exercise.

    Researchers collected information about the sleep habits of more than 16,000 adults in the U.S. They categorized the participants as gardeners, exercisers, or non-exercisers.

    They found that compared to non-exercisers, gardeners were 42 percent less likely to experience sleep problems, and exercisers were 33 percent less likely. The effects of gardening on sleep were dose-dependent, with sleep problems decreasing as weekly gardening time increased. The benefits of gardening were consistent, even after considering other factors that influence sleep, such as age, sex, education level, and body mass index.

    These findings from this observational study suggest that gardening improves sleep better than other forms of exercise or not exercising. Gardening’s sleep-enhancing effects may stem from increased exposure to natural light during the day, regulating the body’s circadian rhythms and, ultimately, sleep. Learn how light exposure, especially early in the day, influences circadian rhythmicity and sleep in this clip featuring Dr. Satchin Panda.

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  • Late-night eating increases the risk of death from diabetes by as much as 131 percent. www.nature.com
    Diet Diabetes Circadian Rhythm Mortality Time-Restricted Eating

    The body’s circadian rhythms – its 24-hour biological, hormonal, and behavioral cycles – are optimized for daytime eating. Consequently, eating in the late evening or nighttime hours may increase a person’s risk of developing chronic diseases, such as type 2 diabetes. A recent study found that nighttime eating increased the risk of premature death from diabetes by as much as 131 percent.

    The investigation included more than 41,000 adults enrolled in NHANES, an ongoing study that assesses the health and nutritional status of people in the U.S. Researchers gathered information about the participants' eating habits (including timing and food quality) and tracked their health and death rates for about nine years.

    They found that compared to eating before 10 p.m., - Eating between 11 p.m. and midnight increased the risk of premature death from diabetes by 131 percent. - Eating between midnight and 1 a.m. increased the risk of premature death from any cause by 38 percent. - Eating between 1 a.m. and 2 a.m. increased the risk of premature death from cancer by 109 percent.

    When they considered the frequency of eating late, they found that eating at night at least once increased the risk of premature death from all causes, including diabetes. Food quality influenced death risk, too, with high-calorie foods increasing the risk of premature death from all causes by 21 percent and from diabetes by 97 percent. Participants who ate late tended to have higher HbA1c, fasting glucose, and oral glucose tolerance test results, indicative of poor glucose metabolism.

    These findings suggest that late-night eating, particularly high-calorie foods, increases the risk of early death from all causes, especially diabetes. Shift work, jet lag, parenting, and modern lifestyles contribute to late-night eating, increasing disease and early death risk. Learn more in this clip featuring Dr. Satchin Panda.

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  • Jet lag causes rats to overeat, linking circadian rhythm disruption to altered appetite regulation and weight gain. www.sciencedaily.com
    Obesity Sleep Hormones Circadian Rhythm

    Circadian rhythms regulate the body’s many physiological processes, including those influencing appetite. Disrupted rhythms, such as those occurring with shift work or jet lag, can alter appetite, contributing to weight gain. A recent study showed that rats with jet lag ate 460 percent more food during their resting phase than non-jet-lagged rats.

    Researchers studied two groups of rats: one that experienced typical light/dark cues (a control group) and one that experienced reversed cues (a “jet-lagged” group) for five days. They monitored the animals' food intake and measured levels of glucocorticoids, a class of hormones that regulate behavior, sleep-wake cycles, and metabolism.

    They found that jet-lagged animals demonstrated dysregulated orexigenic hypothalamic neuropeptide, a glucocorticoid hormone that regulates appetite. This dysregulation increased their desire to eat during their inactive phase (when they typically rest), consuming 460 percent more food than the control group. The overeating rats didn’t gain weight during the study period, likely due to the short duration.

    These findings suggest that circadian rhythm disruption alters glucocorticoid levels in rats, driving increased food consumption. Although the animals didn’t gain weight during the study, longer disruption (as in shift work) may drive considerable weight gain. The study’s authors posited that maintaining a consistent daily schedule and regular meals may help mitigate the effects of circadian rhythm disruption. Learn more about how shift work and jet lag influence circadian rhythms in this clip featuring Dr. Satchin Panda.

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  • High-intensity exercise mitigates sleep-induced metabolic disruptions, offering a potential defense against type 2 diabetes. www.sciencedirect.com
    Exercise Metabolism Sleep Diabetes Circadian Rhythm Mitochondria

    Poor sleep negatively affects metabolism, impairing glucose tolerance and increasing the risk of developing type 2 diabetes. Findings from a recent study indicate that HIIT compensates for the harmful effects of sleep loss on glucose tolerance.

    Researchers assigned 24 healthy young men to one of three five-night sleep protocols: normal sleep (eight hours nightly), sleep restriction (four hours nightly), and sleep restriction with HIIT. Researchers collected muscle biopsies to assess muscle protein synthesis before and after the intervention.

    They found that the group with sleep restriction experienced marked reductions in glucose tolerance, mitochondrial respiratory function, and sarcoplasmic protein synthesis. They also experienced altered diurnal skin temperature rhythms. However, sleep-restricted participants who engaged in HIIT did not experience these disturbances.

    The sarcoplasm is the cytoplasm of muscle cells. Sarcoplasmic protein synthesis is crucial for muscle growth, repair, and maintenance, contributing to overall muscle health and function.

    This study was small, but the findings suggest that sleep restriction impairs metabolic function, circadian rhythmicity, and muscle protein synthesis. However, engaging in HIIT during periods of sleep restriction helps counter these effects. Learn more about the benefits of HIIT in this episode featuring Dr. Martin Gibala.

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  • Bright light exposure may protect the heart by increasing gene activity related to circadian rhythms. www.sciencedaily.com
    Heart Disease Circadian Rhythm

    A 2019 study found that bright light may protect the heart by increasing the activity of a gene involved in circadian rhythms. Bright light also promotes blood flow to the heart.

    Researchers exposed 17 healthy adults to bright light (10,000 LUX, comparable to ambient daylight) for 30 minutes every morning for five days. They collected blood samples from the participants before and after the light exposure at the beginning and end of the intervention.

    They found that bright light triggered the activity of PER2, a gene that regulates the body’s circadian rhythms. Activating PER2 protected against hypoxia – a condition in which low oxygen levels (caused by reduced blood flow) can damage the heart. They also found that bright light triggered the release of adenosine, a chemical that plays a role in regulating blood flow.

    These findings suggest that bright light exposure activates genes involved in circadian rhythms, potentially improving cardiovascular health. This was a very small study, however, and its findings need to be confirmed in larger groups. However, an abundance of research has shown that bright light exposure promotes sleep, which in turn improves many aspects of human health. Learn more in this clip featuring Dr. Matt Walker.

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  • Testosterone levels are subject to a circadian rhythm, peaking in the early morning hours and then falling by at least 43%. (2003) onlinelibrary.wiley.com
    Aging Hormones Circadian Rhythm Testosterone

    From the publication:

    Total testosterone

    Each subject in both the old and young groups showed a marked diurnal variation in serum total testosterone, with a minimum decrease (peak to nadir) of 43% of the peak value. In each group, 50% of the subjects reached a nadir of < 10 nmol/l, while all subjects in both groups had a peak level of > 10 nmol/l. […] A significant difference between the young and older mean total testosterone was shown at three sampling times: 06·00, 07·00 and 07·30 h, when the young group showed a higher mean concentration at each of the three times. In both groups, the acrophase occurred at 07·30 h.

    Bioavailable testosterone

    Both groups display a significant circadian rhythm. No significant difference was demonstrated in mesor or acrophase but a significant difference was shown in amplitude. The acrophase in both groups coincide at 07·24 h, similar to that for the total testosterone. Significant differences between the young and middle-aged groups in the mean bioavailable testosterone were seen at 04·30, 05·30, 06·00, 07·30 and 09·30 h.

    Free testosterone

    A highly significant circadian rhythm was observed in the young group and in the older group. As with the bioavailable testosterone, there was no significant difference between the two groups in mesor and acrophase but a significant difference was seen in amplitude. The acrophase was calculated as occurring at 07·18 h in the young group and 07·05 h in the older men. Significant differences in the mean free testosterone concentration were seen at 05·00, 05·30, 06·00, 06·30, 07·00, 07·30, 09·00, 09·30, 10·00 and 18·00 h.

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  • Circadian desynchrony negatively affected rat Leydig cell function and thus testosterone production. (2022) www.nature.com
    Hormones Circadian Rhythm Mitochondria Testosterone

    From the publication:

    CD [circadian desynchrony] was characterized by changed and decreased rhythmic locomotor activity and reduced blood testosterone. In the Leydig cells changed transcription of the clock genes (Bmal1, Clock, Cry1 and Reverba/b increased while Per1/2 reversed phase) was detected. This was followed by reduced transcription of genes (Star, Cyp11a1, and Hsd3b1/2) primarily involved in mitosteroidogenesis. In parallel, mitochondrial membrane potential (Δψi) and ATP production declined losing their characteristic oscillatory pattern. Also, the main markers of mitochondrial biogenesis (Ppargc1a, Nrf1, Tfam, Cytc), fusion (Mfn2), and mitophagy (Pink1 and Tfeb) were disturbed. Collectively, CD [circadian desynchrony] targets mitochondria in Leydig cells by reducing mitosteroidogenesis, mitoenergetics, and disturbing mitochondrial dynamics. These changes contribute to testosterone decline compromising androgen-dependent functions, including reproduction.

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  • Eating late at night promotes weight gain. www.sciencedaily.com
    Diet Circadian Rhythm Time-Restricted Eating Weight Loss

    Maintaining a healthy body weight presents challenges for many people. Previous research has shown that the timing of food intake plays important roles in managing body weight. Findings from a recent study suggest that late-night eating is counter to the body’s circadian rhythms, increasing the risk of weight gain.

    Circadian rhythms modulate a wide array of the body’s physiological processes, including the production of hormones that regulate sleep, hunger, metabolism, and others, ultimately influencing body weight, performance, and susceptibility to disease. Coordination of meal timing with the circadian rhythm can affect aspects of metabolic health, including glucose regulation and insulin sensitivity.

    The study involved 16 adults (average age, 37 years) who had overweight or obesity. The participants followed an “early” eating schedule and then a “late” eating schedule for six days each, separated by a wash-out period of three to 12 weeks. The researchers controlled the participants' caloric intake, physical activity, sleep, and light exposure throughout the two interventions. They also collected adipose tissue samples from the participants for analysis of gene expression. Participants reported their hunger and appetite.

    The researchers found that when the participants ate later in the day, their hunger and appetite-regulating hormones increased, but their energy expenditure decreased. In addition, eating late altered biochemical pathways involved in fat metabolism and storage.

    These findings suggest that eating late influences appetite, energy expenditure, and molecular pathways in fat tissue, underscoring the role of circadian rhythmicity in bodyweight management. Watch this episode in which Dr. Satchin Panda summarizes tips and strategies that anyone can follow to ensure a healthy circadian pattern.

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  • TNF is associated with reversible depression-like phenotype in hamsters induced by chronic nocturnal dim light exposure. (2012) www.sciencedaily.com
    Brain Depression Circadian Rhythm TNF-Alpha

    From the article:

    While hamsters exposed to light at night for four weeks showed evidence of depressive symptoms, those symptoms essentially disappeared after about two weeks if they returned to normal lighting conditions.

    Even changes in the brain that occurred after hamsters lived with chronic light at night reversed themselves after returning to a more normal light cycle.

    These findings add to the growing evidence that suggest chronic exposure to artificial light at night may play some role in the rising rates of depression in humans during the past 50 years, said Tracy Bedrosian, lead author of the study and doctoral student in neuroscience at Ohio State University.

    “The results we found in hamsters are consistent with what we know about depression in humans,” Bedrosian said.

    […]

    Most importantly, hamsters that lived in dim light showed increased expression of the gene that produces tumor necrosis factor.

    […]

    They found that blocking effects of that protein, called tumor necrosis factor, prevented the development of depressive-like symptoms in hamsters even when they were exposed to light at night.

    […]

    However, hamsters that were returned to a standard light-dark cycle after four weeks of dim light at night saw their TNF levels and even their density of dendritic spines return essentially to normal.

    View full publication

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  • Eating during the day, rather than at night, improves mood. www.sciencedaily.com
    Depression Circadian Rhythm Time-Restricted Eating

    People who regularly keep late hours – for leisure, shift work, or other reasons, such as caring for a newborn – often have misaligned circadian rhythms, placing them at greater risk for depression and anxiety. Research has shown that daytime eating helps realign those rhythms. Findings from a recent study suggest that eating during the day, rather than at night, reduces the risk of depression and anxiety-related disorders.

    The investigators subjected 19 healthy adults (average age, 26 years) to a unique protocol that altered the participants' light exposure, desynchronizing their normal circadian rhythms and mimicking the effects of shift work. During the desynchronized period, half of the participants ate their meals in both the daytime and nighttime, while the other half ate all their meals in the daytime. The investigators monitored the participants' food intake, sleep duration, and depression- and anxiety-like mood levels.

    They found that among participants who ate during both the day and night, depression-like mood levels increased by 26 percent, and anxiety-like mood levels increased by 16 percent. However, participants who ate all their meals during the day did not experience mood changes. Even though the groups' caloric intake, macronutrient intake, physical activity, sleep duration, and eating window duration (12 hours) were identical, eating during the night worsened their moods. As the participants' eating became more misaligned, their symptoms became more severe.

    These findings suggest that restricting mealtimes to daytime hours can offset the mood-altering effects of misaligned circadian rhythms. Learn more about the effects of time-restricted eating on circadian rhythms in this clip featuring Dr. Satchin Panda.

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  • Time-restricted feeding restores healthy circadian oscillations in the ileal microbiota. medicalxpress.com
    Microbiome Circadian Rhythm Time-Restricted Eating

    Compositional oscillations of the gut microbiome are essential for normal peripheral circadian rhythms, both of which are disrupted in diet-induced obesity (DIO). Although time-restricted feeding (TRF) maintains circadian synchrony and protects against DIO, its impact on the dynamics of the cecal gut microbiome is modest. Thus, other regions of the gut, particularly the ileum, the nexus for incretin and bile acid signaling, may play an important role in entraining peripheral circadian rhythms. We demonstrate the effect of diet and feeding rhythms on the ileal microbiome composition and transcriptome in mice. The dynamic rhythms of ileal microbiome composition and transcriptome are dampened in DIO. TRF partially restores diurnal rhythms of the ileal microbiome and transcriptome, increases GLP-1 release, and alters the ileal bile acid pool and farnesoid X receptor (FXR) signaling, which could explain how TRF exerts its metabolic benefits. Finally, we provide a web resource for exploration of ileal microbiome and transcriptome circadian data.

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  • Visceral fat may be less circadian than (healthier) subcutaneous fat: only subcutaneous showed circadian rhythmicity in insulin sensitivity www.sciencedaily.com
    Obesity Insulin Resistance Circadian Rhythm Insulin Metabolic Syndrome Visceral Fat

    From the article:

    Using samples of adipose tissue from both visceral fat and subcutaneous fat from 18 people who underwent gastric bypass surgery, researchers found that subcutaneous fat has an intrinsic circadian rhythm in insulin sensitivity. Insulin sensitivity reached its maximum around noon, and was more than 50 percent higher than at midnight. Interestingly, the rhythm was not observed in visceral fat.

    […]

    “Our study demonstrates that subcutaneous human fat tissue has an internal clock that is able to regulate insulin sensitivity even when outside of the body. This tissue rhythm matches well with what has been observed in humans overall when examining how people cope with a meal or sugar load,”

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  • Excess artificial light exposure increases risk of obesity in preschool aged children www.sciencedaily.com
    Obesity Sleep Circadian Rhythm Development Blue Light

    Artificial light exposure increases the risk for obesity among children. Light is the primary signal that entrains the body’s master clock to set its 24-hour circadian cycle. Consequently, the body is synchronized to external light-dark cycles. In recent decades, exposure to light from artificial sources (rather than natural ones) has increased, paralleling the global increases in obesity among adults. Findings from a 2016 study suggest that exposure to artificial light increases the risk for obesity among children.

    Global health experts estimate that more than 42 million children under the age of five years have obesity, roughly one-fourth of whom live in developing nations. Obesity increases a person’s risk for developing chronic diseases such as type 2 diabetes, heart disease, and some cancers. It also imposes considerable financial costs at the individual, healthcare system, and national level.

    The study involved 48 preschool-aged children receiving daycare services in Australia. The investigators measured the children’s baseline body mass index (BMI), sleep duration and timing, light exposure, and physical activity levels via clinical assessment, parent questionnaires, and light and activity trackers. They repeated these measures 12 months later.

    They found that at baseline, children who had longer early exposure to moderate intensity light (such as that from artificial sources) were more likely to have higher BMI, while children who had longer afternoon exposure to bright light (such as that from natural sources) tended to have lower BMI. At the second assessment, the investigators found that even after taking into account sleep duration and timing, BMI, and activity levels, children who had more total light exposure at baseline (due to having earlier exposure) gained more weight than their peers. Specifically, for every hour earlier that the children were exposed to light, they experienced a 0.6 unit increase in BMI. The investigators posited that although this was a small increase, it could be an indicator of a life-long trajectory toward weight gain.

    These findings suggest that greater light exposure, especially when it occurs early in the day from artificial light sources, contributes to weight gain in children. Interestingly, adults that receive early exposure to bright light typically sleep better – a key to maintaining a healthy weight. Learn more in this clip featuring Dr. Matthew Walker.

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  • Blocking toll-like receptor 4 with Naltrexone reduces alcohol seeking behavior in mice www.sciencedaily.com
    Brain Inflammation Alcohol Circadian Rhythm Behavior Toll-Like Receptors

    The circadian rhythm aspect of drug rewards: “Our body’s circadian rhythms affect the ‘reward’ signals we receive in the brain from drug-related behavior, and the peak time for this reward typically occurs during the evening, or dark phase. We wanted to test what the role of the brain’s immune system might have on that reward, and whether or not we could switch it off.”

    Using naltrexone to block TLR4 reduces alcohol behavior:

    The researchers focused their attention on the immune receptor Toll-like receptor 4 (TLR4). They administered the drug (+)-Naltrexone (pronounced: PLUS-NAL-TREX-OWN), which is known to block TLR4, to mice.

    “Our studies showed a significant reduction in alcohol drinking behavior by mice that had been given (+)-Naltrexone, specifically at night time when the reward for drug-related behavior is usually at its greatest,” Mr Jacobsen says.

    Interestingly and somewhat paradoxically, chronically activating TLR4 through genetic engineering-associated tricks also seems to reduce alcohol seeking in mice.

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  • Immune cell function fluctuates throughout the day. apple.news
    Immune System Circadian Rhythm

    Dendritic cells are white blood cells that play critical roles in launching the body’s immune response. Typically found in peripheral tissues such as the skin, dendritic cells migrate to the lymph nodes, where they interact with T cells to induce immune responses against pathogens, vaccines, and cancer cells. Findings from a new study suggest that dendritic cell migration is subject to circadian rhythm.

    Circadian rhythms are the body’s 24-hour cycles of biological, hormonal, and behavioral patterns. They modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, metabolism, and others. Ultimately, circadian rhythms influence body weight, performance, and disease susceptibility.

    The authors of the study collected skin samples from normal (wild type) mice, mice that lack circadian rhythm, and humans at four distinct times during the day and night, corresponding to morning, day, evening, and night. Mice circadian rhythms are similar to humans', but since mice are nocturnal, the rhythms are “flipped.” The authors quantified the number of dendritic cells in the skin samples using immunofluorescence imaging.

    They found that the migration patterns of dendritic cells followed a circadian pattern, peaking during the rest phase, which occurred early afternoon for mice and early morning for humans. The drivers of this migration were CCL21 (an antimicrobial cell signaling protein) and adhesion molecules (components of an active T-cell mediated immune response), both of which vary in expression along a gradient throughout the day.

    These findings suggest that dendritic cell migration into lymph vessels is subject to circadian rhythm. They also underscore the importance of considering the time of day at which vaccines or immunotherapy treatments are administered.

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  • Prebiotics may help restore circadian rhythms. www.sciencedaily.com
    Microbiome Circadian Rhythm

    Circadian rhythms play critical roles in human health. Maintaining these rhythms can be challenging, especially for people who work night shifts or travel across multiple time zones. Findings from a new study suggest that prebiotics can help restore the body’s natural rhythms.

    Prebiotics are food components that support the maintenance of a healthy microbiota and create an environment that is conducive to its survival. Fructo-oligosaccharides, galacto-oligosaccharides, and trans-galacto-oligosaccharides are the most common prebiotics. Their fermentation by gut microbiota produces short-chain fatty acids, including lactic acid, butyric acid, and propionic acid. Many commonly consumed fruits and vegetables, such as apples, bananas, and legumes, contain prebiotics.

    The authors of the study fed rats either a prebiotic-enriched diet or a standard diet. After the rats had been on their respective diets for five weeks, the authors either flipped their light/dark schedules (roughly equivalent to flying across 12 time zones) or left them on a normal schedule once a week for eight weeks. They measured the animals' sleep, brain activity, core body temperature, and locomotor activity. They also collected fecal samples from the animals and identified the types and number of gut microbes present.

    The rats that ate the prebiotic-enriched diet resumed their normal sleep-wake cycles, core body temperature, and activity levels faster than the rats that ate the standard diet. The rats on the prebiotic diet also had greater abundance of several health-promoting microbes, including Ruminiclostridium 5, compared to those on the standard diet. Previous research indicates that Ruminiclostridium 5 is associated with improved sleep.

    These findings suggest that eating a diet rich in prebiotics can help restore normal circadian rhythms following disruption, such as would occur after working shifts or traveling. Learn more about the effects of shiftwork on human health in this episode featuring Dr. Satchin Panda.

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  • Circadian dysregulation of DNA repair drives increased cancer risk among shift workers. www.eurekalert.org
    Cancer Circadian Rhythm

    Large, population-based studies have identified robust links between shift work and increased cancer risk. Much of this risk is associated with disruptions in the body’s circadian rhythms, the 24-hour cycles of biological, hormonal, and behavioral patterns. A recent study suggests that circadian dysregulation of DNA repair mechanisms drives the increased cancer risk associated with shift work.

    Circadian rhythms influence many physiological pathways associated with cancer, such as regulation of the cell cycle, cell proliferation, and inflammation. These rhythms also influence mechanisms that repair DNA damage – which can drive mutations that promote cancer.

    The study involved 14 healthy men and women (22 to 34 years old) who participated in a simulated shift work experiment at a sleep laboratory. Half of the participants completed a simulated night shift schedule for three nights in which they were awake from 6 p.m. to 10 a.m. The other half completed a simulated day shift schedule for three days in which they were awake from 6 a.m. to 10 p.m. The study participants received a snack and provided blood samples every three hours. After completing their three days of respective shift work schedules, they underwent a 24-hour study protocol in which they were kept awake for 24 hours in low light in a semi-recumbent posture and received hourly snacks. Every three hours the study investigators took a blood sample from the participants. They analyzed the white blood cells from the samples and then exposed the cells to radiation in the morning and evening.

    The authors found that the rhythms of many of the cancer-related genes in the white blood cells were different among the night shift workers compared to the day shift workers. Notably, genes related to DNA repair that showed distinct rhythms of expression during the day shift lost their rhythmicity during the night shift. They also found that the night shift workers' cells that were exposed to radiation in the evening showed more DNA damage – an indication that they were more vulnerable to external stressors.

    These findings suggest that night shift work alters circadian DNA repair mechanisms and promotes DNA damage, thereby increasing cancer risk. One strategy for ameliorating the harmful effects of night shift work is time-restricted eating. Learn more in this episode featuring circadian rhythm expert Dr. Satchin Panda..

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  • Exercise can reset the circadian clock in the muscles of mice. www.sciencedaily.com
    Exercise Circadian Rhythm Muscle

    The circadian rhythm is the body’s 24-hour cycle of biological, hormonal, and behavioral patterns that, when disrupted, has profound implications for human healthspan. Findings from a recent study suggest that a single bout of exercise can reset the circadian clock in the skeletal muscles of mice.

    The circadian clock coordinates gene expression in nearly all cells in a time-dependent manner. Cues from the environment, known as zeitgebers, can alter the circadian clock in a process known as entrainment. Light acts as the primary zeitgeber, but activity, stress, and eating also affect circadian timing. Exercise affects body temperature, heart rate, and many other metabolic parameters and might also entrain the circadian clock.

    The current study investigated whether exercise would act as a zeitgeber for the circadian clock in the skeletal muscles of mice. Transgenic mice completed a sixty-minute bout of moderate‐intensity exercise at different times during their rest or active periods. The authors of the study observed that mice exercised during their typical rest period exhibited a shift in the muscle circadian clock. However, mice exercised during their active phase showed no effects on the circadian rhythm.

    To factor out the hormonal and temperature effects of exercise, the authors developed an in vitro model system using time‐synchronized rodent muscle cells. They subjected these cells to an electrical current, to simulate muscle contractions, and measured the expression of known molecular clock‐related genes. The authors found that electrical stimulation altered the expression of clock genes, and shifted the circadian clock in a pattern similar to that observed in the mouse model system.

    Taken together these findings suggest that a single bout of exercise can alter the circadian clock — making it a true zeitgeber. The specific effect of exercise on the circadian clock depends on the time when it is performed. While further studies are needed to determine if these findings translate to humans, the authors propose that shift workers might benefit from timed exercise to offset some of the negative effects of circadian disruption.

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  • A disrupted sleep-wake cycle may be an early warning sign of Parkinson's disease. www.sciencedaily.com
    Parkinson's Sleep Circadian Rhythm

    Parkinson’s disease, or PD, is a neurodegenerative disorder identified by the death of dopamine-producing neurons in the part of the brain that controls movement. The disease typically manifests later in life and is characterized by tremors and a shuffling gait. However, other regions of the brain are also affected, and sleep disturbances are a common non-motor feature of PD. Findings from a new study suggest that a disrupted circadian rhythm is a risk factor for PD.

    The circadian rhythm is the body’s 24-hour clock that modulates a wide array of physiological processes, including the production of hormones that regulate sleep, hunger, metabolism, and others, ultimately influencing body weight, performance, and susceptibility to disease. As such, circadian rhythmicity may have profound implications for human healthspan. The circadian rhythm changes with age and older adults have less deep, more fragmented sleep. Alterations in the circadian rhythm are more profound in people with PD, even in the early stages of the disease before symptoms develop.

    Previous research in animals has demonstrated that damage to circadian-related neurons occurs during the presymptomatic stages of PD. The current study investigated whether a disordered circadian rhythm in later life is associated with an increased risk of developing PD in humans.

    In a longitudinal prospective study, the authors recruited 2,930 healthy, community-dwelling older men without PD. The authors measured the rest-activity rhythms of the participants by having them wear a device on their wrist that measured activity, known as an actigraph. The authors collected recordings of activity and sleep patterns over three continuous 24 hour periods and plotted them on a graph for each participant. During the following 11 years, the men were asked if they had received a PD diagnosis and whether they were taking medications for the disease. The actigraphs revealed that participants with a less robust circadian rhythm, as evidenced by features including reduced activity and drowsiness during the day and fragmented sleep, had an increased risk of developing PD over the subsequent 11-year period.

    These findings suggest that an altered circadian rhythm may occur years in advance of clinical signs of PD and might be a useful prognostic marker. Even for community-dwelling older adults, reduced daily activity, daytime drowsiness, and fragmented sleep may be signals that warrant attention. Further research is needed to determine if these findings also apply to women and younger individuals.

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  • Autophagy Regulates the Liver Clock and Glucose Metabolism by Degrading CRY1 papers.ssrn.com
    Nutrition Metabolism Biomarkers Circadian Rhythm Behavior Autophagy Protein

    The circadian clock coordinates behavioral and circadian cues with the availability and utilization of nutrients. Proteasomal degradation of clock repressors, e.g., cryptochrome (CRY)1 maintains periodicity of the clock. Whether autophagy, a quality control pathway, degrades circadian proteins remains unknown. Here we show that circadian proteins BMAL1, CLOCK, REV-ERB, and CRY1 are lysosomal targets, and that α macroautophagy (hereafter autophagy) specifically degrades CRY1. Autophagic degradation of CRY1, an inhibitor of gluconeogenesis, occurs in a diurnal window when rodents rely on gluconeogenesis, suggesting that degradation of CRY1 is time-imprinted to maintenance of blood glucose levels. CRY1 contains several light chain 3 (LC3)-interacting region (LIR) motifs, which facilitate the interaction of cargo proteins to the autophagosome marker LC3. Using mutational analyses, we identified two distinct LIRs on CRY1 that exert circadian control over blood glucose levels by regulating CRY1 degradation, revealing CRY1 LIRs as potential targets in regulation of glucose metabolism.

    Toledo, Miriam and Tarabra, Elena and Batista-Gonzalez, Ana and Merlo, Paola and Feng, Daorong and Sarparanta, Jaakko and Botrè, Francesco and Pessin, Jeffrey E. and Singh, Rajat, Autophagy Regulates the Liver Clock and Glucose Metabolism by Degrading CRY1 (2018). Available at SSRN: https://ssrn.com/abstract=3155564 or http://dx.doi.org/10.2139/ssrn.3155564

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  • Cell-Autonomous Regulation of Astrocyte Activation by the Circadian Clock Protein BMAL1 papers.ssrn.com
    Brain Aging Circadian Rhythm Neuron Glutathione Neurons Protein

    Abstract

    Circadian clock dysfunction is a common symptom of aging and neurodegenerative diseases, though its impact on brain health is poorly understood. Astrocyte activation occurs in response to diverse insults, and plays a critical role in brain health and disease. We report that the core clock protein BMAL1 regulates astrogliosis in a synergistic manner via a cell-autonomous mechanism, and via a lesser non-cell-autonomous signal from neurons. Astrocyte-specific Bmal1 deletion induces astrocyte activation in vitro and in vivo, mediated in part by suppression of glutathione-s-transferase signaling. Functionally, loss of Bmal1 in astrocytes promotes neuronal death in vitro. Our results demonstrate that the core clock protein BMAL1 regulates astrocyte activation and function in vivo, elucidating a novel mechanism by which the circadian clock could influence many aspects of brain function and neurologic disease.

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  • After exposure to daytime bright light (6.5 hours), evening use of a tablet for two hours did not affect sleep in healthy young students. www.sciencedaily.com
    Sleep Circadian Rhythm Blue Light

    Getting bright light throughout the day could be just as important for improving sleep as avoiding blue light exposure at night.

    After exposure to daytime bright light (6.5 hours), evening use of a tablet for two hours did not affect sleep in healthy young students.

    The evening tablet use did not affect sleepiness and saliva melatonin levels before sleep, nor did it change the time to fall asleep or subsequent sleep. It has previously been shown that early bright light exposure can ameliorate some of the suppressive effects of evening blue light has on melatonin levels.

    To learn more about the importance of early bright light exposure on improving sleep quality, check out my podcast with Dan Pardi that talks about a lot of interesting points relevant to this…

    https://www.foundmyfitness.com/episodes/dan-pardi

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  • Using biomarkers to determine body circadian time www.jci.org
    Biomarkers Circadian Rhythm

    BACKGROUND. The circadian clock is a fundamental and pervasive biological program that coordinates 24-hour rhythms in physiology, metabolism and behaviour, and it is essential to health. Whereas time-of-day adapted therapy is increasingly reported to be highly successful, it needs to be personalized since internal circadian time is different for each individual. In addition, internal time is not a stable trait, but is influenced by many factors including genetic predisposition, age, gender, environmental light levels and season. An easy and convenient diagnostic tool is currently missing.

    METHODS. To establish a validated test, we followed a three-stage biomarker development strategy: (i) using circadian transcriptomics of blood monocytes from 12 individuals in a constant routine protocol combined with machine learning approaches, we identified biomarkers for internal time; (ii) these biomarkers were migrated to a clinically relevant gene expression-profiling platform (NanoString), and (iii) externally validated using an independent study with 28 early or late chronotypes.

    RESULTS. We developed a highly accurate and simple assay (BodyTime) to estimate the internal circadian time in humans from a single blood sample. Our assay needs only a small set of blood-based transcript biomarkers and is as accurate as the current gold standard dim light melatonin onset method at smaller monetary, time and sample number cost.

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  • Acid Suspends the Circadian Clock in Hypoxia through Inhibition of mTOR. - PubMed - NCBI www.ncbi.nlm.nih.gov
    Cancer Metabolism Stress Circadian Rhythm Autophagy

    Citation: Cell. 2018 Jun 28;174(1):72-87.e32. doi: 10.1016/j.cell.2018.05.009. Epub 2018 May 31.

    Abstract Recent reports indicate that hypoxia influences the circadian clock through the transcriptional activities of hypoxia-inducible factors (HIFs) at clock genes. Unexpectedly, we uncover a profound disruption of the circadian clock and diurnal transcriptome when hypoxic cells are permitted to acidify to recapitulate the tumor microenvironment. Buffering against acidification or inhibiting lactic acid production fully rescues circadian oscillation. Acidification of several human and murine cell lines, as well as primary murine T cells, suppresses mechanistic target of rapamycin complex 1 (mTORC1) signaling, a key regulator of translation in response to metabolic status. We find that acid drives peripheral redistribution of normally perinuclear lysosomes away from perinuclear RHEB, thereby inhibiting the activity of lysosome-bound mTOR. Restoring mTORC1 signaling and the translation it governs rescues clock oscillation. Our findings thus reveal a model in which acid produced during the cellular metabolic response to hypoxia suppresses the circadian clock through diminished translation of clock constituents.

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  • New research suggests that mammals may become less responsive to light as a signal that resets the circadian clock as they age. www.sciencedaily.com
    Aging Circadian Rhythm

    The research was done in mice and found that the glutamate receptor (NMDA), which used to transmit light information, became less effective in resetting the circadian clock during the aging process.

    It is unclear how much of this translates to humans and whether this means that older people may need more bright light exposure to reset the circadian clock, which in turn affects sleep onset and quality.

    Light entrains the circadian clock to our 24-hour day through melanopsin, a photopigment in the eye that is specialized for communicating circadian information instead of image formation.

    Additionally, the eye is known to undergo structural changes with age, which can also impact circadian training. Light information is decoded by a subset of retinal ganglion cells expressing the melanopsin photopigment. Melanopsin is specialized for communicating circadian information.

    To learn more how the important role early bright light exposure plays in circadian training, check out my first podcast episode with Dr. Satchin Panda, who discovered melanopsin. You can click on the timeline for the specific time points when we discuss the role bright light plays in resetting the clock.

    https://www.foundmyfitness.com/episodes/satchin-panda

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  • Fat Tissue Has Receptors for Sunlight and They Affect Fat Metabolism blog.humanos.me
    Circadian Rhythm Fat Nitric Oxide Neurons Vitamin A Blue Light Protein

    You probably already know that ambient light regulates circadian rhythms by interacting with light-sensitive neurons in the eye.

    But let’s review anyway: In full white light (which contains all colors of light), the rays of the blue and green light spectrum activate melanopsin, a photosensitive protein in specific cells of the retina in the back of the eye. When light hits these cells, a signal transmits information to the brain’s master clock. By detecting various intensities and tones of light, the brain can keep track of what time of day it is.

    This is relatively well established. We also know that sunlight can stimulate the production of vitamin D and nitric oxide, both of which have important effects on health. But are these all of the effects that light has on our physiology?

    It has been known for several decades that a small percentage of blue light can penetrate human skin, and can even reach white subcutaneous adipose tissue. But the relevance of this finding on our physiology was not obvious.

    Curiously, it has also been reported that high OPN4 (the gene that encodes the photopigment melanopsin) mRNA levels are found in human subcutaneous fat. Kind of weird: what the heck are these light-sensitive eye proteins doing in our fat tissue? Additionally, we now know that fat cells contain transient receptor potential cation (TRPC) channels – membranes that are found in the retina that open in response to varying intensities of light.

    So, we know that blue light can get to subcutaneous fat tissue, and fat cells seem to have the machinery needed to respond to the signal that is transmitted by light. Very interesting. Is it possible that visible light penetrates the skin, and exerts physiological effects by activating a melanopsin / TRPC channel signaling pathway in human fat? And if so, could exposure to visible light have an impact on the regulation of body fat? The answer appears to be yes.

    My guest in this episode (inadvertently) found the answer to this novel questions…

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  • Young men had increased body fat in response to later meal timing independent of food content and activity level. ajcn.nutrition.org
    Diet Obesity Circadian Rhythm Time-Restricted Eating

    The study found that the timing of food intake relative to melatonin onset, a marker of a person’s biological night, is associated with higher percent body fat. Individuals with high body fat percentages consumed most of their calories shortly before going to sleep when melatonin levels were high, compared to individuals with lower percentages of body fat.

    To learn more about the benefits of time-restricted eating and how to practice it check out my podcasts with Dr. Satchin Panda. To learn more about how late night eating affects cancer risk check out my podcast with Dr. Ruth Patterson. Both podcasts are available on iTunes and YouTube (called foundmyfitness).

    Satchin Panda podcast: https://www.youtube.com/watch?v=-R-eqJDQ2nU Ruth Patterson podcast: https://www.youtube.com/watch?v=8qlrB84xp5g

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  • Late-night eating increases weight gain, raised insulin, fasting glucose, cholesterol & triglycerides in small trial. www.sciencedaily.com
    Insulin Resistance Fasting Circadian Rhythm Fat Insulin Triglycerides Time-Restricted Eating

    A small clinical trial finds that eating later in the day (12 pm to 11 pm) increased weight gain, raised insulin, fasting glucose, cholesterol, and triglyceride levels compared to eating earlier in the day (8 am to 7 pm).

    In the small study, each of the nine healthy weight adults underwent each of the two conditions: daytime eating (three meals and two snacks between 8 a.m. and 7 p.m.) for eight weeks and delayed eating (the same three meals and two snacks eating from noon to 11 p.m.) for eight weeks after a 2-week washout period. This is a small trial and needs to be repeated but is in line with another study that showed when healthy adults eat meals that are identical for breakfast, lunch, or dinner, the postprandial glucose increase is lowest after breakfast and highest after dinner even though the meals were 100% identical.

    For more on meal timing and time-restricted eating…check out my podcasts with the experts, Dr. Satchin Panda and Dr. Ruth Patterson on youtube and iTunes.

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