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.