Too Much Sleep or Too Little Increases Mortality Risk

HELSINKI, Finland, Oct. 1 -- Sleep excesses one way or the other can carry a roughly 20% greater mortality risk over two decades, investigators here found.

Men, in particular, had a significant increase in the associations between natural death and both stable long and stable short sleep, Christer Hublin, M.D., Ph.D., of the Finnish Institute of Occupational Health, and colleagues, reported in issue of Sleep.

The findings add to evidence of sleep's impact on health and mortality but also show that the association is complicated. "The exact mechanisms [of the association] remain unclear, and they should be assessed in experimental settings and other longitudinal studies," Dr. Hublin and colleagues concluded.

"Although the effect of sleep on mortality is fairly modest compared to . . . smoking or components of the metabolic syndrome, it is still of considerable significance as it is associated with several common disorders such as cardiovascular diseases and diabetes," they added.

Studies published over the past 20 years have generally revealed a U-shaped curve association between sleep length and mortality, with the lowest mortality associated with about seven hours of sleep, the authors stated.

Multiple studies have revealed an increased mortality risk in association with prolonged sleep (eight hours or more). In contrast, the impact of short sleep on mortality has tended to decrease after adjustment for other factors known to be associated with mortality, such as smoking, alcohol use, and physical inactivity.

Dr. Hublin and colleagues reviewed data from the Finnish Twin Cohort, involving 21,268 twins ages 18 and older who completed questionnaires between 1975 and 1981. The questionnaires included items related to sleep habits.

On the basis of the survey responses, participants were categorized as:

• Short sleepers (less than seven hours)
• Average sleepers
• Long sleepers (more than eight hours)
• Sleeping well
• Sleeping fairly well
• Sleeping fairly poorly or poorly
• Nonusers, infrequent users, or frequent users of hypnotics or tranquilizers

Proportional hazard models were used to calculate hazard ratios for mortality during 1982 to 2003 by sleep-related variables and their combinations. The primary findings were increased mortality risks associated with:

• Short sleep-men +26% and women +21%
• Long sleep-men +24% and women +17%
• Frequent hypotnotic use-men +31%, women +39%

Snoring as a covariate did not change the results. The effect of sleep on mortality varied by age, and the strong effects were seen in young men.

Overall, sleep length and quality changed in about a third of participants in the study during the period reviewed. The change in sleep patterns manifested in an impact on mortalilty. Among men stable short sleep was associated with a 34% increase in natural deaths and stable long sleep with a 29% increase. During 1975 to 1981, stable short sleepers had a 62% increase in the risk of death from external causes.