Too much, too little sleep increases ischemic risk in postmenopausal women
Study highlights:
• Sleeping nine hours or more a night significantly increases the risk for
ischemic stroke among post menopausal women.
• Sleeping less than 6 hours showed a modest increase risk of stroke, but was
reported by twice as many women.
• The findings cannot be applied to other groups.
DALLAS, July 18 – Postmenopausal women who regularly sleep more than nine
hours a night may have an increased risk of ischemic stroke, researchers
reported in Stroke: Journal of the American Heart Association.
Compared to women sleeping seven hours, the risk of ischemic stroke was 60-70
percent higher for those sleeping nine hours or more, said lead author
Jiu-Chiuan Chen, M.D., Sc.D., assistant professor of epidemiology at the
University of North Carolina’s School of Public Health in Chapel Hill.
“After accounting for all common clinical conditions predictive of stroke, we
found this increase was statistically significant: sleeping nine hours or more
is strongly associated with increased risk of ischemic stroke,” he said.
Researchers also found that women who slept six hours or less were at 14 percent
greater stroke risk than those who slept seven hours a night. Nearly twice as
many women reported sleeping less than six hours (8.3 percent) than those who
reported sleeping nine hours or more (4.6 percent).
“The prevalence in women of having long sleep duration is much lower than
having sleep duration less than six hours. So the overall public health impact
of short sleep is probably larger than long sleep,” Chen said. “This study
provides additional evidence that habitual sleep patterns in postmenopausal
women could be important for determining the risk of ischemic stroke.”
The findings apply only to postmenopausal women and cannot be applied to other
groups, including men and younger women. Postmenopausal women 50- to
79-years-old may be more susceptible to the detrimental effects of sleep
deprivation than others.
“Our study population is a very specific group, and the duration of sleep
needed for optimal health probably differs for various population groups,” he
said. “People who feel that their sleep problems are a burden to their daytime
activities are encouraged to discuss their concerns with physicians who can
better interpret their significance and offer advice in the context of their
overall health.”
Three large previous studies have addressed the role of sleep duration in
coronary artery disease
and/or stroke. They yielded mixed results and didn’t account for the many
factors that may increase the risk of cardiovascular disease and stroke,
including: age, race, socioeconomic factors such as family income and
employment, smoking, depression, exercise, hormone therapy in postmenopausal
women, high-blood pressure, high cholesterol, diabetes, and obstructive sleep
apnea.
Chen and his colleagues included known risk factors that might confound any
apparent association of sleep duration and ischemic stroke in this analysis of
data from the multi-ethnic Women’s Health Initiative Observational Study. The
study’s 93,676 women were 50 to 79 years old at the time of their enrollment
at 40 U.S. clinical centers. Researchers conducted the study from 1994 to 2005.
Researchers asked the women how long they typically slept each night. The
results were: five hours or less, 8.3 percent; six hours, 26.9 percent; seven
hours, 37.5 percent; eight hours, 22.7 percent; nine hours, 4.0 percent and 10
hours or more, 0.6 percent.
After accounting for the common risk factors for ischemic stroke, the increased
relative stroke risks compared to the seven-hour-sleep group were: 14 percent
for six hours or less sleep; 24 percent for eight hours of sleep; and 70 percent
for nine or more hours of sleep.
Among the team’s other results:
• Long sleep durations were associated with being retired or unemployed;
smoking, being physically inactive or having cardiovascular disease, diabetes,
hypertension, high cholesterol or depression.
• Overweight women and minority women were more likely to sleep six hours or
less.
• Women with current hormone therapy were less likely to sleep six hours or
less.
• Income, physical activity, depressive symptoms and other cardiovascular risk
factors correlated with sleep duration, but didn’t fully account for the link
between stroke and sleep patterns.
Medical, psychosocial and lifestyle variables included in their analysis
could not completely explain the increased ischemic stroke risk associated with
short and long sleep among postmenopausal women. But Chen said many studies have
documented physiological consequences of sleep deprivation.
“Our data do not imply that if women with long sleep cut their sleep hours
they would be at a lower risk,” Chen emphasized. “At this point, we still
cannot determine that long sleep causes ischemic stroke. The observed increase
in stroke risk in long sleepers may be due to some unmeasured factors, such as
undiagnosed sleep disorders, although we did attempt to account for that in our
analysis.”
“Further studies are needed to help us understand the possible mechanisms
involved in the associations found in this study,” he said, “because there
are very limited neurobiological data relating long sleep to an increased risk
of coronary heart disease or ischemic stroke that also is found in other large
epidemiologic studies.”
Co-authors are Robert L. Brunner, Ph.D.; Hong Ren, M.S.; Sylvia
Wassertheil-Smoller, Ph.D.; Joseph C. Larson, M.S.; Douglas W. Levine, Ph.D.;
Matthew Allison, M.D.; Michelle J. Naughton, Ph.D. and Marcia L. Stefanick,
Ph.D. Individual author disclosures can be found on the manuscript.
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Editor’s note: For more information on stroke, visit the American
Stroke Association Web site: www.strokeassociation.org.
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American Heart Association: http://www.americanheart.org/presenter.jhtml?identifier=1200000