Insufficient sleep--a population-based study in adults.

STUDY OBJECTIVES Insufficient sleep (sleep deprivation) is a common problem of considerable health, social, and economical impact. We assessed its prevalence and associations, and the role of genetic influences. DESIGN Panel study based on questionnaires administered in 1981 and 1990. SETTING/PATIENTS 12.423 subjects aged 33-60 years included in the Finnish Twin Cohort, representative of the Finnish population. INTERVENTIONS N/A. MEASUREMENTS A difference of 1 hour between the self-reports of the sleep need and the sleep length was considered insufficient sleep. Associations with education, life style, work, psychological characteristics and sleep-wake variables were assessed. Structural equation modelling techniques were used to compare genetic models among monozygotic and dizygotic twin pairs. RESULTS In 1990, the prevalence of insufficient sleep was 20.4% (16.2% in men and 23.9% in women). 44% of those with insufficient sleep in 1981 also had it 9 years later (Spearman correlation for persistence 0.334). In multivariate analyses, the strongest positively associated factors were daytime sleepiness (women: odds ratio 3.87, 95% confidence limits 3.24-4.63/men: 3.77, 2.98-4.75), insomnia (2.48, 1.92-3.19/2.91, 2.17-3.90), not able to sleep without disturbance (1.95, 1.47-2.60/2.54, 1.66-3.89), and evening type (2.10, 1.65-2.69/1.73, 1.25-2.41). Among men, also weekly working hours > or =75 was strongly associated (3.23, 1.54-6.78). "Not working" was negatively associated in both genders (0.68, 0.51-0.89/0.59, 0.42-0.83). Two thirds of the interindividual variability in the liability to insufficient sleep was attributed to non-genetic factors. CONCLUSIONS Insufficient sleep is a common and long-standing condition, most strongly associated with sleep/wake variables. One third of the liability to it is attributed to genetic influences. Sleep sufficiency should be assesssed in health examinations of working adults.