Sleeping too little or too much can significantly increase the risk of mortality, according to a study conducted in Britain the results of which were published in the United States Saturday.

• A decrease in sleep duration among participants sleeping six, seven or eight hours was associated with a 110 percent excess risk of cardiovascular mortality, said the study authored by Jane Ferrie of the University College London Medical School in London.

• The study, authored by Jane E. Ferrie , PhD, of the University College London Medical School in London, U.K., focused on 10,308 participants between 35 and 55 years of age. Baseline screening (Phase 1), conducted between 1985 and 1988, involved a clinical examination and a self-administered questionnaire. Data collection at Phase 3 (1992-1993) also included a clinical examination (8,104 participants) and questionnaire (8,642 participants). 

• According to the results, U-shaped associations were observed between sleep at             Phase 1 and Phase 3 and subsequent all-cause, cardiovascular and non-cardiovascular mortality. A decrease in sleep duration among participants sleeping six, seven or eight hours at baseline was associated with a 110 percent excess risk of cardiovascular mortality. However, an increase in sleep duration among those sleeping seven or eight hours at baseline was associated with a 110 percent excess risk of non-cardiovascular mortality. Adjustment for the socio-demographic factors, existing mortality and health-related behaviors measured left these associations largely unchanged.

• In terms of prevention, our findings indicate that consistently sleeping seven or eight hours per night is optimal for health, said Dr. Ferrie. The indication that mortality rates are lower in participants who slept five to six hours or less at Phase 1 but who reported extended hours of sleep at Phase 3 implies that increasing sleep duration in short sleepers is likely to have health benefits. In contrast to this, the finding that an increased duration of sleep among those sleeping seven to eight hours is associated with higher levels of mortality implies that sleep restriction .

The study is published in the December 1 issue of SLEEP, which is the official journal of the Associated Professional Sleep Societies, LLC.

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