Excessive daytime sleepiness, objective napping and 11-year risk of Parkinson's disease in older men

It is unknown whether subjective daytime sleepiness or objective napping could precede the risk of Parkinson's disease (PD) in the long term.

We studied 2920 men (mean age 76 years) without a history of PD and followed them for 11 years. Excessive daytime sleepiness (EDS) was defined as having an Epworth Sleepiness Scale score >10. Objective naps were defined as ≥5 consecutive minutes of inactivity as measured by actigraphy, and napping duration was the accumulated time of naps outside the main sleep period. We used logistic regression to compare PD risk across four groups: no EDS& napping <1 h/day (N = 1739, 59.5%; referent group), EDS& napping <1 h/day (N = 215, 7.4%), no EDS& napping ≥ 1 h/day (N = 819, 28.1%) and EDS& napping ≥ 1 h/day (N = 147, 5.0%).

We identified 106 incident PD cases over 11 years. After multivariable adjustment, men with napping  ≥  1h/day alone were twice as likely [odds ratio (OR) = 1.96, 95% confidence interval (CI) 1.25-3.08], and men with both EDS and napping  ≥ 1 h/day were almost three times as likely to develop PD (2.52, 1.21-5.27), compared with the referent group. Compared with those with naps for <30 min, men who napped for  ≥1 h/day had more than double the risk of PD. No association was found for EDS alone and PD risk. Further adjustment for chronotype and circadian stability, or excluding PD cases identified within 2 years after napping measurements, showed similar results.

Objective long napping rather than subjective EDS was prospectively associated with a higher risk of PD in older men. Objective measures of napping might be valuable as a preclinical marker for PD.