Poor Sleep Signals a Greater Cardiovascular Risk for Women

By Judith Groch
DURHAM, N.C, March 11 -- Women who can't get to sleep have higher levels of biomarkers for cardiovascular disease and diabetes than do men who sleep poorly, a study here found.
Women who are poor sleepers also have greater psychological distress than men who sleep poorly, Edward Suarez, Ph.D., of Duke University, and colleagues reported online in Brain, Behavior, and Immunity.
Sleep quality ratings were similar in men and women, but women had dramatically different risk profiles, including high levels of C-reactive protein, interleukin-6, and insulin, the researchers found.
Recent observations from large epidemiological studies have suggested that poor sleep is more strongly associated with higher risks of cardiovascular disease and hypertension in women than in men, but no study has examined the physiological mechanisms that could explain the gender differences, the researchers wrote.
Their study was designed to investigate whether gender moderates the relation of sleep and sleep-related symptoms to indices of inflammation, coagulation, insulin resistance, and psychosocial distress, all factors associated with an increased risk of cardiovascular and metabolic disorders.
The researchers recruited 210 apparently healthy non-smoking middle-age men (115) and women (95) without a history of sleep disorders. Participants (ages 18 to 65) were recruited from the surrounding community.
The Pittsburgh Sleep Quality Index (PSQI) was used to assess sleep quality and frequency of sleep symptoms.
Because over-the-counter sleep medications may influence a number of variables, all analyses were also done on patients (92%) who reported no use of medicine during the previous month.
About 40% of the men and women were classified as poor sleepers, defined as problems falling asleep, taking 30 minutes or more to fall asleep, or awakening frequently. However, their sleep profiles were dramatically different.
Age was not associated with the total sleep quality index except for daytime disturbance, for which increasing age was linked to fewer problems with daytime sleepiness. Self-reported sleep quality and symptoms of sleep problems did not differ by ethnicity.
In multivariate-adjusted models, overall poor sleep quality, more frequent problems falling asleep (>2 nights/week) and longer periods to fall asleep (>30 min) were associated with greater psychosocial distress (hostility, anger, depression, and social support), and higher fasting insulin, fibrinogen, and inflammatory biomarkers, but only for women.
The average number of hours slept was not associated with inflammatory biomarkers. However, the time it took to fall asleep was significant, such that among women, longer time to falling asleep was associated with IL-6 (b=0.001, t=22.40, P=0.02) and C-reactive protein (b=0.01, t=1.97, P=0.05).
On the other hand, time to fall asleep was not associated with inflammatory biomarkers in men.
The total sleep quality score did not predict fibrinogen levels, the researchers said. However, women, but not men, who had trouble falling asleep had higher fibrinogen levels than those reporting no problems falling asleep (adjusted mean SEM) = 231.0 mg/dL) than those reporting no problems (adjusted mean SEM = 210.8 mg/dL).
Higher C-reactive protein and fibrinogen levels have been shown to indentify individuals at risk of becoming diabetic due to insulin resistance but not poor insulin secretion, the researchers said.
Interestingly, Dr. Suarez said, it appears that it is not so much overall poor sleep quality that was associated with greater risk, but rather the length of time it takes to fall asleep. Of women who took half an hour or more to fall asleep, 35% had C-reactive protein levels at or above 3.0 mg/L, and 32% had insulin-resistance values above 1.96.
The results also indicated that poor sleep quality was associated with higher BMI in women (b=0.50, t=2.16, P=0.03) but not in men. Daytime dysfunction was also worse for these women, but not for men.
For men, higher levels of testosterone may blunt the damaging consequences of poor sleep. Higher testosterone is associated with lower C-reactive protein, greater insulin sensitivity, and lower BMI, the researchers said.
One possible explanation for these findings, the researchers said, is that they reflect differences in the actions of the amino acid tryptophan, the neurotransmitter serotonin, and the neurohormone melatonin. Some studies have suggested gender differences for the direct and indirect effects of these substances on sleep and sleep onset.
Study limitations included the fact that the study was not designed to test directionality, leaving open the question of whether, for example, sleep disturbances promote psychological stress, or vice versa.
Use of the self-report scale in assessing sleep problems was another limitation, and an important caveat, the investigators said, was recruitment that was not targeted to individuals with a history of sleep disorders.
That sleep is a modifiable factor suggests its usefulness as a target for clinical intervention programs aimed at reducing primary disease risk, the researchers said.
This study was supported by a grant from the National Institutes of Health. No financial conflicts of interest were reported.
Primary source: Brain, Behavior, and ImmunitySource reference:Suarez EC, et al "Self-reported symptoms of sleep disturbance and inflammation, coagulation, insulin resistance, and psychological distress: Evidence for gender disparity" Brain, Behavior, and Immunity 2008; DOI:10.1016/j.bbi.2008.01.011.