NEW YORK (Reuters Health) - People who have a tough time getting a good night's sleep are more likely to become dissatisfied with their lives later on, a new study in twins from Finland shows.

While poor sleep and life dissatisfaction each showed a strong tendency to be inherited, they did not seem to share the same genetic roots, Dr. Tiina Paunio of the National Public Health Institute in Helsinki and colleagues found. This suggests, they conclude, that something about sleeping badly in itself may affect "the brain, emotions, and mood."

A few studies have looked at the relationship between life dissatisfaction -- which reflects the feeling of well-being and mental functioning -- and sleep quality, the researchers note, but none have looked at how the two are associated over time. To investigate, they surveyed a group of 18,631 same-sex twins in 1975 and again in 1981.

In 1975, about 9 percent of the study participants reported dissatisfaction with life, and they were likely to be dissatisfied in 1981. However, their sleep quality did not deteriorate over this period.

On the other hand, the people who said they slept "rather poorly or poorly" in 1975 were 2.4 times more likely to be dissatisfied with life in 1981.

When the researchers adjusted for all of the factors that could have played a role in the relationship, such as health problems, smoking and drinking habits, and physical activity level, they found that poor sleep independently tripled the likelihood of life dissatisfaction.

The findings suggest that bad sleep quality may lead to dissatisfaction with life, but that the reverse is not true, the researchers conclude.

"Finding a temporal relation between poor sleep and subsequent life dissatisfaction is likely not to represent solely the dynamic reflections of the same underlying genetic factors," they write. "Rather, it is likely to illustrate more causal mechanisms underlying the neurophysiologic effect of poor sleep on brain function, and the experience of feeling of dissatisfaction in life."

SOURCE: American Journal of Epidemiology, January 15, 2009.

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