Volume 94, No.3, May-June 2008

Wake-Up Call on Sleep

Sleeping woman
Sir Edward Burne-Jones / The Bridgeman Art Library

Poor sleep may be more harmful to women than to men, according to a new study by Duke Medical Center researchers. Poor sleepers may have trouble falling asleep, awaken frequently during the night, or both.

The study, which appears online in the journal Brain, Behavior and Immunity, indicates that, for both men and women, poor sleep is associated with greater psychological distress as well as higher levels of biomarkers that indicate an elevated risk of heart disease and type 2 diabetes. But it also shows that those associations are significantly stronger in women.

The researchers focused on a sample of 210 apparently healthy, middle-aged men and women without any history of sleep disorders. None smoked or took any medications on a daily basis, and investigators excluded any women who were on hormone therapy, which some studies have shown to alter sleep patterns in some women.

Using a standardized sleep-quality questionnaire, participants rated various dimensions of their sleep over the previous month. Additional measures assessed the extent of any depression, anger, hostility, and perceived social support from friends and family.

Blood samples taken from the volunteers were measured for levels of biomarkers associated with an increased risk of heart disease and diabetes, including insulin and glucose levels, fibrinogen (a clotting factor), and two inflammatory proteins known as C-reactive protein and interleukin-6.

The researchers found that about 40 percent of the men and the women were classified as poor sleepers, which they defined as having frequent problems falling asleep, taking thirty or more minutes to fall asleep, or awakening frequently during the night. But while their sleep quality ratings were similar, men and women had dramatically different risk profiles.

"We found that for women, poor sleep is strongly associated with high levels of psychological distress and greater feelings of hostility, depression, and anger," says Edward Suarez, an associate professor in the department of psychiatry and behavioral sciences and the lead author of the study. "In contrast, these feelings were not associated with the same degree of sleep disruption in men."

Women who reported higher degrees of sleep disruption also had higher levels of all the biomarkers tested. The results were so dramatic that of those women considered poor sleepers, 33 percent had C-reactive protein levels associated with high risk of heart disease, Suarez says.

"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," Suarez says. "Women who reported taking a half an hour or more to fall asleep showed the worst risk profile."