Is Napping Associated With Risk of Parkinson’s Disease?

BALTIMORE—Older men who nap for more than an hour per day are more likely to develop Parkinson’s disease over 11 years of follow-up, compared with those who nap for less than an hour per day and do not have excessive daytime sleepiness, according to a study described at the 32nd Annual Meeting of the Associated Professional Sleep Societies.

Yue Leng, PhD

Self-reported daytime sleepiness alone was not associated with increased risk, said Yue Leng, PhD, a postdoctoral researcher at the University of California, San Francisco.

The findings suggest that objective measures of napping might be valuable preclinical markers of Parkinson’s disease.

The mechanism underlying the association is unclear. It is possible that the ongoing degeneration in brain regions involved in the 24-hour sleep–wake cycle leads to increased napping in people who later develop Parkinson’s disease, she said.

“Excessive daytime sleepiness and daytime napping are common in older adults, especially those with Parkinson’s disease,” Dr. Leng said. Whether excessive daytime sleepiness or napping precedes the development of Parkinson’s disease and may be risk factors is not well understood, however. “There is a lack of objectively measured naps and also a lack of longitudinal studies. In fact, we are unaware of any longitudinal studies that have used objectively measured napping in relation to Parkinson’s disease risk.”

To examine the longitudinal association between objectively measured napping duration and risk of Parkinson’s disease, Dr. Leng and colleagues analyzed data from the Osteoporotic Fractures in Men Study (MrOS), a large, longitudinal, multicenter study of community-dwelling older men. They excluded men with Parkinson’s disease at baseline. The analysis included data from more than 2,900 men who had napping and sleep measures at baseline between 2003 and 2005 and were followed up for development of Parkinson’s disease over 11 years.

The investigators used actigraphy to measure napping. Participants wore a sleep watch on the dominant wrist for at least five consecutive 24-hour periods. The researchers defined napping as having at least five consecutive minutes of inactivity outside of the main sleep period. They defined excessive daytime sleepiness as a score greater than 10 on the Epworth Sleepiness Scale.

The researchers identified Par­kinson’s disease using physician diagnosis or Parkinson’s disease medication use. Their analysis adjusted for age, BMI, smoking, physical activity, depression, comorbidities, global cognition scores, medication use, and nighttime sleep variables (ie, efficiency, duration, and apnea–hypopnea index).

“The highest risk was in those who reported daytime sleepiness and had objective napping for at least an hour per day,” Dr. Leng said. These participants had more than twice the risk of developing Parkinson’s disease, compared with a reference group that did not have daytime sleepiness and napped for less than one hour per day (odds ratio, 2.52).

Participants who napped for at least an hour per day but did not report excessive daytime sleepiness also had increased risk (odds ratio, 1.96).

The results indicate that objectively measured napping, rather than self-reported excessive daytime sleepiness, is important for Parkinson’s disease risk, Dr. Leng said.

Sensitivity analyses that excluded patients who developed Parkinson’s disease within two years after baseline and only included physician-confirmed cases of Parkinson’s disease had similar results.

Actigraphy is limited in its ability to differentiate between napping and inactivity, Dr. Leng noted. In addition, the results cannot be generalized to women and younger populations, she said.

—Jake Remaly

Suggested Reading

Leng Y, Goldman SM, Cawthon PM, et al. Excessive daytime sleepiness, objective napping and 11-year risk of Parkinson’s disease in older men. Int J Epidemiol. 2018 Jun 4 [Epub ahead of print].