Parkinson Disease and Sleep: Does Daytime Napping Impact the Risk for PD?

Increased duration and frequency of daytime napping may be associated with an increased risk for Parkinson disease (PD); however, no causal relationship between napping frequency and PD risk was observed, according to study results published in BMC Medicine.

Researchers conducted a prospective cohort study with Mendelian randomization to explore the relationship between daytime napping duration and frequency and PD incidence. Data were sourced between 2006 and 2010 from UK Biobank recruits aged 37 to 73. Three major resurveys were conducted in 2012 to 2013, 2014, and 2019. Daytime napping duration and frequency were determined using a wrist-worn accelerometer and responses to a questionnaire asking whether or not the patient has a nap during the day, respectively. The systemic immune-inflammation index (SII) and polygenic risk score (PRS) were also calculated. The association between daytime napping duration and frequency and PD risk was estimated using Cox proportional hazards regression. Two-sample Mendelian randomization analyses were conducted to explore the causal association between daytime napping frequency and PD risk.

A total of 393,302 participants (mean age, 56.27; women, 52.5%; White, 91.7%) were included in the study, the median follow-up period of which was 12.18 years. Of the 78,141 patients with available accelerometer-measured daytime napping data, 224,646 (57.1%) reported never or rarely taking a daytime nap, 148,094 (37.7%) reported taking an occasional nap, and 20,562 (5.2%) reported usually napping during the day.

Patients who reported napping sometimes vs never had a 13% higher PD risk (hazard ratio [HR], 1.13; 95% CI, 1.03-1.23; P =.009). Compared with those who reported never taking daytime naps, patients who reported frequent daytime napping had a 33% increased risk for PD (HR, 1.33; 95% CI, 1.14-1.55; P =.001).

More specifically, patients who napped more than 1 hour per day had a 54% increased risk for PD (HR, 1.54; 95% CI, 1.11-2.16; P =.01). Further, afternoon naps (1 PM-3 PM: HR, 1.02; 95% CI, 1.01-1.03; P <.001; 4 PM-6 PM: HR, 1.01; 95% CI, 1.00-1.02; P =.001) were associated with an increased risk for PD, while morning naps were not.

A positive linear relationship between daytime napping duration and PD risk was demonstrated in the dose-response analysis.

No significant interaction was identified between daytime napping duration (P =.178) or frequency (P =.225) and PRS in their effect on PD development.

According to the Mendelian randomization analysis, there was no significant association between daytime napping and PD incidence (odds ratio [OR], 0.816; 95% CI, 0.510-1.304).

Study limitations include potential unknown confounders and pleiotropic bias, as well as the predominantly European population.

“Larger GWAS [genome-wide association studies]-based cohort studies and MR [Mendelian randomization] studies are warranted to explore potential causal relationships,” the study authors concluded.