Daytime napping, nighttime sleeping, and Parkinson disease

Abstract

Preliminary evidence suggests that daytime sleepiness may predate clinical diagnosis of Parkinson disease. The authors examined daytime napping and nighttime sleeping durations, reported in 1996-1997 by 220,934 US NIH-AARP Diet and Health Study participants, in relation to Parkinson disease diagnoses at 3 clinical stages: established (cases diagnosed before 1995, n = 267), recent (1995-1999, n = 396), and prediagnostic (2000 and after, n = 770). Odds ratios and 95% confidence intervals were derived from multivariate logistic regression models. Longer daytime napping was associated with higher odds of Parkinson disease at all 3 clinical stages: the odds ratios comparing long nappers (>1 hour/day) with nonnappers were 3.9 (95% confidence interval: 2.8, 5.6) for established cases, 2.2 (95% confidence interval: 1.7, 3.0) for recent cases, and 1.5 (95% confidence interval: 1.2, 1.9) for prediagnostic cases. Further control for health status or nighttime sleeping duration attenuated the association for established cases but made little difference for recent or prediagnostic cases. In the nighttime sleeping analysis, a clear U-shaped association with Parkinson disease was observed for established cases; however, this association was attenuated markedly for recent cases and disappeared for prediagnostic cases. This study supports the notion that daytime sleepiness, but not nighttime sleeping duration, is one of the early nonmotor symptoms of Parkinson disease.

Figure 1.

Numbers of hours of daytime napping in relation to Parkinson disease diagnosis at different clinical stages for NIH-AARP Diet and Health Study participants, 1996–2006. Black lines: adjusted for age, sex, race, physical activity, smoking status, and caffeine intake; grey lines: also adjusted for self-reported health status. All P for trend < 0.0001 except for prediagnostic cases in the basic model (P = 0.0003) and with additional adjustment for self-reported health status (P = 0.0022). Established cases: diagnosed before 1995; recent cases, diagnosed in 1995–1999; prediagnostic cases: diagnosed in 2000 and after. Actual values for odds ratios and 95% confidence intervals are provided in Web Table 2 (which is posted on the Journal’s Web site (http://aje.oupjournals.org/)). CI, confidence interval; NIH, National Institutes of Health.

Figure 2.

Numbers of hours of nighttime sleeping in relation to Parkinson disease diagnosis at different clinical stages for NIH-AARP Diet and Health Study participants, 1996–2006. Black lines: adjusted for age, sex, race, physical activity, smoking status, and caffeine intake; grey lines: also adjusted for self-reported health status. Established cases: diagnosed before 1995; recent cases, diagnosed in 1995–1999; prediagnostic cases: diagnosed in 2000 and after. Actual values for odds ratios and 95% confidence intervals are provided in Web Table 3 (which is posted on the Journal’s Web site (http://aje.oupjournals.org/)). CI, confidence interval; NIH, National Institutes of Health.