February 2 (HealthDay News) -- Inflammation may play a role in the health of people who sleep too little or too much, according to a U.S. study that included 614 people.

Previous studies have linked both short and long sleep duration with an increased risk for coronary heart disease, diabetes, obesity, and death. Chronic elevations in inflammation-regulating cytokines are also associated with an increased risk of health problems such as heart disease and diabetes.

In this new study, participants completed a questionnaire about their sleep habits and spent one night in a sleep lab. The mean self-reported habitual sleep duration was 7.6 hours, while the mean sleep duration measured in the sleep lab was 6.2 hours.

Each additional hour of self-reported sleep duration was associated with an 8 percent increase in levels of C-reactive protein (CRP) and a 7 percent increase in levels of interleukin-6 (IL-6). Both CRP and IL-6 are inflammation-regulating cytokines. Each hour of verified sleep reduction was associated with an 8 percent increase in tumor necrosis factor, another inflammation-regulating cytokine.

The researchers also found that participants who slept longer were significantly younger and that short sleep duration was associated with an increased prevalence of diabetes, hypertension and obstructive sleep apnea.

"The most surprising finding was that we found different relationships based on how sleep was measured," lead author Dr. Sanjay R. Patel, assistant professor of medicine at Case Western Reserve University in Cleveland.

Patel and colleagues said the differing patterns of association with cytokine levels suggest that self-reported sleep duration reveals chronic (long-term) sleep patterns, while sleep lab testing provides an acute (short-term) measurement . In addition, the two methods of measuring sleep duration may be influenced differently by underlying factors of sleep habits, such as stress or mood, which may have a direct effect on cytokine levels.

The study was published in the Feb. 1 issue of the journal Sleep.

SOURCE: American Academy of Sleep Medicine, news release, Feb. 1, 2009