Sleep well to live well

Editorial note: This article was originally published in the past and has been updated to include more recent studies and improve clarity and transparency. The content is for informational purposes only and does not replace medical advice.

IN BRIEF

• Sleep disturbances and fragmentation of sleep-wake rhythms have been associated with an increased risk of developing Parkinson's disease in observational studies.
• Objective measures from actigraphy and accelerometry indicate that reduced amplitude, lower daytime activity, and more fragmented rhythms correlate with a higher prospective risk of Parkinson's in the elderly population.
• There are plausible biological mechanisms (oxidative stress, inflammation, sleep-related protein alterations) but associations are not proof of causality.
• Some specific sleep disorders (e.g., motor behaviors in REM sleep) are among the most robust prodromal markers of future neurodegenerative disease.
• Interpreting these data requires caution: for the individual, the absolute risk remains variable and depends on many factors. For clinical concerns, consult a doctor.

Abstract: what does science say?

Definition: "circadian rhythm" refers to the daily alternation of activity and rest that regulates the sleep-wake cycle. Recent studies have measured these rhythms with wearable devices (actigraphy/accelerometry) and clinical sleep assessments.

What available evidence shows: in population cohorts and longitudinal studies, objective metrics of rhythmicity loss (reduced amplitude, increased fragmentation, lower daytime activity) have been associated with an increased likelihood of developing Parkinson's in the medium to long term. These associations have been observed in various national and international samples and in follow-ups ranging from a few to over ten years.

What depends on dose, frequency, context: associations vary with age, physical activity level, comorbidities, and other sleep disorders. The extent and duration of fragmentation or daytime sleepiness seem important as indicators; however, there is no single "dose" that defines certain risk.

Interpretive limitations: most of the evidence is observational, therefore it does not prove that sleep disturbances cause Parkinson's. It is possible that sleep alterations are an early sign (prodrome) of the disease or that common factors (e.g., degeneration of brainstem nuclei) cause both conditions.

What it means in practice

For the general reader: the results indicate that marked changes in sleep and daily activity rhythms should not be ignored, especially in the elderly population. Symptoms such as persistent daytime sleepiness, very fragmented sleep, and abnormal behaviors during sleep (e.g., violent movements during REM sleep) warrant specialist clinical evaluation. However, current literature cannot recommend a single preventive action aimed exclusively at reducing the risk of Parkinson's.

When to consult a doctor: if sleep disturbances are new, worsen over time, or are accompanied by mood changes, cognitive disturbances, or early motor signs (rigidity, subtle tremor, slowness), a clinical evaluation should be sought. Diagnoses and diagnostic pathways are individual and require anamnesis, neurological examination, and, when indicated, sleep tests.

Interventions and their limits

Sleep hygiene interventions, regular physical activity, and comorbidity management can improve sleep quality and general well-being without any claim to prevent Parkinson's. Some targeted therapies (e.g., melatonin therapy for specific sleep disorders) may be useful for symptoms, but their effectiveness in modifying the risk of neurodegenerative disease has not been demonstrated.

Main evidence and studies (and what they say)

Longitudinal studies with actigraphy and accelerometry have documented robust associations between reduced amplitude of activity rhythms, increased 24-h fragmentation, and subsequent risk of Parkinson's in old age [1]. In a cohort of almost 3,000 elderly men, those with the weakest rhythmicity had a threefold increased risk of developing the disease compared to the most rhythmic [1].

Independent data on a larger scale have confirmed the direction of the association: analyses of tens of thousands of UK participants show that 24-h metrics derived from accelerometers are associated with an increased risk of Parkinson's and other dementias [2]. Similar results emerge from population studies correlating subjective worsening of sleep and future diagnosis of parkinsonism [3].

Studies analyzing specific aspects of sleep (daytime sleepiness, fragmented sleep, daytime naps) indicate that both the quality and distribution of activity during the day can have prognostic value: some recent works show dose-response associations between prolonged daytime naps and increased risk of Parkinson's [4].

Links with neuropathological and biomolecular data

Post-mortem research and animal studies suggest plausible mechanisms: sleep fragmentation has been correlated with signs of neuronal pathology typical of parkinsonism in the brains of clinically unaffected populations, and sleep-wake cycles influence the metabolism and rearrangement of brain proteins involved in neurodegeneration [5][6]. Furthermore, circadian clock proteins appear to regulate cellular processes related to oxidative stress and neuronal homeostasis, offering biological plausibility to the observed link [7].

Key takeaways

• Associations exist between objectively measured sleep-wake rhythm alterations and a higher probability of Parkinson's diagnosis in longitudinal studies [1][2].
• Most evidence is observational: a statistical link does not equate to causality; sleep alterations may be an early sign of the disease or share common causes with Parkinson's [1][3].
• Some sleep disorders, such as REM sleep behavior disorder (RBD), are among the strongest predictors of neurodegeneration and warrant specialist evaluation [8].
• Plausible mechanisms include alterations in brain protein turnover, inflammation, and oxidative stress linked to sleep disturbances; however, these remain hypotheses to be confirmed with interventional studies [6][7].
• For general health, improving sleep quality through non-pharmacological strategies is reasonable; but there is no definitive evidence that such measures alone prevent Parkinson's.

Limitations of the evidence

Observational studies: most available research is observational and prospective. This means that we observe a temporal relationship between sleep alterations and subsequent diagnosis, but we cannot establish with certainty that the former causes the latter. It is possible that small neuropathological changes, present years before diagnosis, cause both sleep disturbances and motor disease.

Methodological limitations: metrics derived from actigraphy and accelerometry measure movements and activity rhythms, not directly internal biological processes; moreover, data quality can be influenced by individual habits, medication use, comorbidities, and differences between devices. Population studies differ in age, sex, diagnostic criteria, and follow-up duration, reducing generalizability.

Context variability: shift workers, chronic use of certain medications, chronic diseases, and socio-environmental factors can alter rhythms and confound analyses. Interpreting results requires attention to confounding factors and possible selection biases.

Why experimental studies are needed

To shift the level of evidence from association to causality, studies are needed that intervene on rhythms (e.g., randomization to treatments that stabilize the circadian rhythm) and verify whether these modifications reduce the progression of biological markers or the clinical onset of Parkinson's. At present, some small trials on chronobiological therapies and therapeutic light show effects on day-night and symptoms, but not on reducing the long-term risk of disease [7][9].

Editorial conclusion

Recent literature reinforces the idea that the quality and integrity of sleep-wake rhythms are connected to the future risk of developing neurodegenerative diseases, including Parkinson's disease. However, the observational nature of the evidence calls for caution: sleep disturbances may be early signs of the disease rather than independent causes. For the public, the invitation is not to underestimate significant changes in sleep and to seek clinical evaluation when symptoms are persistent or associated with other neurological signs. For the scientific community, the goal is to conduct studies that compare interventions targeting circadian rhythms with long-term biological and clinical endpoints.

Editorial note (before bibliography): This update has been prepared following criteria of transparency and verifiability. The article summarizes published evidence and does not provide personalized therapeutic recommendations. For clinical indications, please refer to your trusted doctor.

SCIENTIFIC RESEARCH

1. Leng Y, Blackwell T, Cawthon PM, Ancoli‑Israel S, Stone KL, Yaffe K. Association of circadian abnormalities in older adults with an increased risk of developing Parkinson disease. JAMA Neurol. 2020;77(10):1270–1278. https://doi.org/10.1001/jamaneurol.2020.1623 [1]
2. Winer JR, Lok R, Weed L, He Z, Poston KL, Mormino EC, et al. Impaired 24‑h activity patterns are associated with an increased risk of Alzheimer’s disease, Parkinson’s disease, and cognitive decline. Alzheimer Res Ther. 2024;16:35. https://doi.org/10.1186/s13195-024-01411-0 [2]
3. Lysen TS, Darweesh SKL, Ikram MK, Luik AI, Ikram MA. Sleep and risk of parkinsonism and Parkinson’s disease: a population‑based study. Brain. 2019;142(7):2013–2022. https://doi.org/10.1093/brain/awz113 [3]
4. Daytime napping and the incidence of Parkinson’s disease: a prospective cohort study with Mendelian randomization. BMC Med. 2024;22:326. https://doi.org/10.1186/s12916-024-03497-7 [4]
5. Sohail S, Yu L, Schneider JA, Bennett DA, Buchman AS, Lim ASP. Sleep fragmentation and Parkinson’s disease pathology in older adults without Parkinson’s disease. Mov Disord. 2017;32(12):1729–1737. https://doi.org/10.1002/mds.27200 [5]
6. Holth JK, Fritschi SK, Wang C, et al. The sleep‑wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans. Science. 2019;363(6429):880–884. https://doi.org/10.1126/science.aav2546 [6]
7. Musiek ES, Lim MM, Yang G, et al. Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration. J Clin Invest. 2013;123(12):5389–5400. https://doi.org/10.1172/JCI70317 [7]
8. Postuma RB, Gagnon JF, Vendette M, Fantini ML, Massicotte‑Marquez J, Montplaisir J. Quantifying the risk of neurodegenerative disease in idiopathic REM sleep behavior disorder. Neurology. 2009;72(15):1296–1300. https://doi.org/10.1212/01.wnl.0000340980.19702.6e [8]
9. Excessive daytime sleepiness in Parkinson’s disease: A systematic review and meta‑analysis. Park Relat Disord. 2021; (meta‑analysis). https://doi.org/10.1016/j.parkreldis.2021.02.016 [9]