Is self-reported morbidity related to the circadian clock?

Morningness and eveningness preference, an endogenous component of the circ adian clock, is characterized by an interindividual difference in circadian phase and requires of humans a specific timing of behavior. The biological rhythms of morning and evening types are consequently phase shifted with f ixed socioeconomic constraints. The impact of this phase shift on health is widely debated. The purpose of the authors' study was to determine the inf luence of morningness/eveningness preference on self-reported morbidity and health in an active population. A total of 1165 nonshift workers of the Fr ench national electrical and gas company, enrolled in the GAZEL cohort and aged 51.3 +/- 3.3 years, were included in this study. They replied by mail with a completed questionnaire, including morningness/eveningness preferenc e, self-reported morbidity, subjective sleep patterns, and daytime somnolen ce and sleeping schedules for 3 weeks, during the spring of 1997. Annual se lf-reported health impairments were assessed with the annual general questi onnaire of the GAZEL cohort for 1997. After adjustment for age, sex, and oc cupational status, morningness-like and eveningness-like participants repor ted a specific worse self-reported morbidity. Whereas morningness was assoc iated with worse sleep (p = 0.0001), eveningness was associated with feelin g less energetic (p = 0.04) and physical mobility (p = 0.02). These relatio nships were observed even in good sleepers, except for physical mobility. A fter adjustment for confounding variables, eveningness-like participants re ported more sleep (p = 0.0004) and mood (p = 0.00018) disorders than mornin gness-like participants. Morningness/eveningness preference was related to specific chronic complaints of insomnia: morningness was related with diffi culty in maintaining sleep (p 0.0005) and the impossibility to return to sl eep in the early morning (p 0.0001) (sleep phase-advance syndrome); evening ness was related to difficulty in initiating sleep (p = 0.0001) and morning sleepiness (p = 0.0001). In good sleepers, morningness was related with sl eep phase-advance syndrome (p = 0.0001) and eveningness with morning sleepi ness (p = 0.0001). In conclusion, the expression (phase advance or delay) o f the circadian clock could be related to worse self-reported morbidity and health. These findings must be verified by further epidemiological studies , but they suggest that the impossibility to return to sleep in the early m orning is not only associated with age.