March 21 (HealthDay News) -- Women suffer more damage to their cardiovascular health from poor sleep than men do, and researchers at Duke University Medical Center believe they've determined why.

They found that poor sleep is associated with greater psychological distress and higher levels of biomarkers associated with increased risk of type 2 diabetes and heart disease. They also found that these associations are stronger in women than in men.

"This is the first empirical evidence that supports what we have observed about the role of gender and its effects upon sleep and health," study author Edward Suarez, an associate professor in the department of psychiatry and behavioral sciences, said in a prepared statement.

"The study suggests that poor sleep -- measured by the total amount of sleep, the degree of awakening during the night, and most importantly, how long it takes to get to sleep -- may have more serious health consequences for women than for men," he said.

The study was published online in the journal Brain, Behavior and Immunity.

Even though women are twice as likely as men to report sleep problems, most sleep studies in the past have focused on men, said Suarez, who added that this pattern has been slowly changing in recent years.

This new study included 210 healthy middle-aged women and men without any history of diagnosed sleep disorders. None of them smoked or took any medications on a daily basis. The participants filled out a standard sleep quality questionnaire and were assessed for levels of depression, anger, hostility and perceived social support. Blood samples from the participants were analyzed for levels of biomarkers associated with increased risk of diabetes and heart disease.

About 40 percent of the participants were classified as poor sleepers, meaning they had frequent problems falling asleep or awoke frequently during the night. While the men and women in the study had similar sleep quality ratings, their risk profiles were dramatically different, the researchers said.

"We found that for women, poor sleep is strongly associated with high levels of psychological distress, and greater feelings of hostility, depression and anger. In contrast, these feelings were not associated with the same degree of sleep disruption in men," Suarez said.

Women who were poor sleepers also had higher levels of C-reactive protein and interleukin-6 -- inflammation biomarkers associated with increased risk of heart disease and higher levels of insulin.

"Interestingly, it appears that it's not so much the overall poor sleep quality that was associated with greater risk, but rather the length of time it takes a person to fall asleep that takes the highest toll. Women who reported taking a half hour or more to fall asleep showed the worst risk profile," Suarez said.

He suggested the sleep/health risk differences between men and women may be partly due to variations in the activity of the number of naturally occurring substances in the body, such as the amino acid tryptophan, the neurotransmitter serotonin, and the neurohormone melatonin.

"All of these substances are known to affect mood, sleep, onset of sleep, inflammation and insulin resistance," said Suarez, who plans further research into the link between poor sleep and health risk in women and men.

SOURCE: Duke University, news release, March 10, 2008