A single night of poor sleep can reduce your insulin sensitivity by up to 25%, fueling glycation-induced cellular damage that cumulatively accelerates biological aging.

This means even one bad night can significantly impact your body's ability to manage blood sugar levels.

But it's not just about how many hours you sleep—a new study highlights that bedtime matters, too.

Participants who didn't sleep enough or who went to bed after midnight had larger spikes and more variability in blood sugar (as measured by continuous glucose monitors or CGM) compared to those getting at least 8 hours of sleep or going to bed before midnight.

The worst combination for glucose control was inadequate sleep combined with a late bedtime. The shocking finding? Going to bed early didn't make up for getting too little sleep.

In today's email, we will explore what these findings mean for how we should think about sleep and our metabolic health plus some sleep hygiene strategies and protocols to help us stay healthy when we don't sleep enough!

Sleep is essential for metabolic regulation

Sleep restriction—even mild reductions of just one hour per night—can have profound negative effects on metabolic health, including increased insulin resistance, elevated glucose levels, and disrupted hunger hormones. That's concerning, as nearly one-third of Americans routinely sleep fewer than the recommended 7 to 9 hours per night, putting them at increased risk for conditions like type 2 diabetes and cardiovascular disease.

Studies show that reducing sleep by just one hour per night over three days significantly elevates fasting insulin and glucagon levels and reduces insulin sensitivity. Even more extreme sleep debt, like getting four fewer hours per night over several days or more, can lead to a 40% slower glucose clearance rate and impair glucose effectiveness by 30%, mirroring early diabetes. Chronic sleep loss also raises HbA1c levels, leading to the formation of harmful advanced glycation end-products (AGEs) which stiffen blood vessels and contribute to cardiovascular diseases and hypertension.

How does this happen? In my interview with sleep expert Dr. Matthew Walker he explains how sleep deprivation causes the beta cells of the pancreas to become less responsive to glucose elevations—they don't release enough insulin. Muscle and fat cells also stop being as sensitive to the insulin that is released. With less insulin available and a lower response from our body's glucose sinks, blood sugar levels stay elevated after meals.

Additionally, sleep deprivation disrupts satiety hormones, increasing ghrelin (the "hunger hormone") and reducing leptin (the "satiety hormone"). This imbalance leads to higher hunger and increased consumption of unhealthy, processed foods. Pair that with insulin resistance and it's a recipe for metabolic dysregulation!

The importance of going to bed at the right time, consistently, has also become an important topic of discussion. It all comes back to circadian rhythms in metabolism. We are more insulin sensitive early in the day and less so later in the day. Shift workers or individuals experiencing circadian disruption have increased risks for impaired glucose tolerance and diabetes because a misalignment between internal circadian clocks and external environmental cues (e.g., altered sleep-wake cycles, eating at inappropriate biological times) leads to decreased insulin sensitivity and impaired beta-cell responsiveness.

So, if we want to truly optimize metabolic health, we have to think about sleeping enough and sleeping at the right time. According to a new study, it's important to do both.

To unravel the relationship between sleep behaviors and glucose control, the study first categorized participants according to their sleep duration and timing trajectories over the span of 10 years—an important aspect of the study because it represents their chronic sleep habits rather than a single snapshot of their current or past sleep habits. Sleep duration was defined as severely inadequate (4.1–4.7 hours per night), moderately inadequate (5.5–6 hours per night), mildly inadequate (6.8 to 7.2 hours per night), and adequate (8 to 8.4 hours per night).
 

Sleep onset timing—what time the participants went to bed each night—was defined as early sleep onset (before midnight) and late sleep onset (after midnight).

Short sleepers have more glucose variability

Compared to adequate sleepers who got 8 hours or more per night, inadequate sleepers had larger glucose excursions and more variable daily glucose levels, indicating poorer blood glucose control.
 

Severely inadequate sleep—4.1 to 4.7 hours per night—was also associated with having less time in a glucose range of 70 to 180 mg/dL (3.0 to 10 mmol/L).

Glucose variability is higher in people with a late bedtime

Going to bed late also predicted worse glycemic outcomes—participants with a bedtime after midnight had greater variability in their glucose levels than those who reported an earlier bed time.
 

While inadequate sleep and a late bedtime were independently associated with poor glycemic control, their combined effects were even more harmful.
 

Participants with a late bedtime and inadequate sleep had high glucose variability—only those sleeping adequately (8 or more hours per night) were immune from effects of a later bedtime. The worst thing for metabolic health was having a late bedtime and only sleeping 4.1–4.7 hours per night, which was associated with the worst glycemic control.

One of the more surprising findings was that going to bed early did not protect against the effects of inadequate sleep. The participants who went to bed early but only achieved between 4.1 and 7.2 hours of sleep per night still had worse glycemic control measures than participants who slept adequately and went to bed early.

Final thoughts

When it comes to sleep, optimizing timing and duration is important—having one without the other could cause large and highly variable glucose fluctuations, which puts you at risk for cardiometabolic diseases.
 

Does this mean that staying out too late or getting a few less hours of sleep on the weekend will lead to diabetes? Not at all. A few nights of poor sleep cannot undo the benefits of a consistent and sufficient sleep schedule. What's novel about this study is that it measured participants' chronic sleep habits, showing the deleterious effects of years and years of insufficient sleep and late bed times rather than the effects of a few days. Diabetes doesn't develop overnight, and if you currently have poor sleep habits, it's not too late to make a change.
 

If you are looking improve your sleep hygiene, try these tips:

• Bright morning light exposure and avoiding evening blue light.
• Sleeping in a cool, dark room.
• Avoiding food at least three hours before bedtime.
• Regular physical exercise.
• Limiting caffeine intake, especially in the afternoon.

For situations when extended sleep isn't feasible, high-intensity interval training (HIIT) can mitigate many negative effects of poor sleep. Just a few sessions per week significantly improve glucose tolerance, mitochondrial function, and overall metabolic health, even when sleep-restricted.

Ultimately, combining consistent exercise, optimal sleep hygiene, and mindful meal timing offers powerful protection against the metabolic consequences of insufficient sleep. Sometimes we need all the help we can get.

To hear more of my thoughts on sleep and glucose regulation, check out these member Q&A episodes that we've handpicked to accompany this email.

Q&A #61 with Dr. Rhonda Patrick (8/3/2024)

• 19:51 - The single best thing you can do to improve glucose levels
• 21:07 - How building muscle helps your body manage glucose
• 22:36 - Why refined carbs (high glycemic load) hurt glucose regulation
• 25:32 - Why eating carbs last can blunt glucose spikes
• 27:00 - The two supplements proven to lower HbA1c
• 30:27 - How much sleep do you really need for healthy glucose levels?
• 31:55 - Can cinnamon and apple cider vinegar actually improve blood sugar?

Q&A #54 with Dr. Rhonda Patrick (12/2/2023)

• 39:29 - Does supplementing with inositol improve sleep?
• 42:33 - How inositol may quiet a racing mind before bed
• 44:19 - Does glycine supplementation lead to better sleep?
• 47:22 - The supplement Rhonda takes before bed
• 1:12:10 - Why you should take Oura Ring data with a grain of salt
• 1:13:02 - The most reliable indicator of good sleep
• 1:13:50 - How to improve deep sleep with heat exposure
• 1:14:36 - Does an irregular bedtime sabotage deep sleep?

With appreciation,

Rhonda and the FMF Team