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.
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.