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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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