Regular daytime dozing forewarns of a significantly increased risk of stroke in older Americans, researchers reported at the American Stroke Association's International Stroke Conference 2008.
Stroke risk was two- to four-fold greater in those with moderate dozing. This suggests that daytime dozing "may be an important and novel stroke risk factor," said Bernadette Boden-Albala, Ph.D., lead author of the study.
In this study, dozing refers to a person unintentionally falling asleep.
Among 2,153 participants in a prospective study with an average follow-up of 2.3 years, the risk of stroke was 2.6 times greater for those classified as doing "some dozing" compared to those with "no dozing." Those in the "significant dozing" group had a 4.5 times higher risk.
"Those are significant numbers," said Boden-Albala, an assistant professor of neurology at Columbia University's College of Physicians and Surgeons in New York City. "We were surprised that the impact was that high for such a short period of time."
Sleep scientists previously have found evidence that people who experience apnea, brief periods when breathing stops during sleep, have an increased stroke risk. Research indicates that daytime sleepiness can result from sleeping poorly because of nighttime apnea.
Researchers studied a community-based cohort as part of the long-term Northern Manhattan Study (NOMAS), which began in 1990 and included men and women ages 40 and older. It's the first effort investigating stroke risk factors in whites, blacks and Hispanics living in the same community.
No study participants had suffered a stroke. At study entry, their average age was 73 years and 64 percent were women. The racial-ethnic mix was 60 percent Hispanic, 20 percent black and 18 percent white.
In 2004, Boden-Albala and her colleagues began collecting daytime dozing data annually using the Epworth Sleepiness Scale. The Epworth scale asks people to rate their frequency of dozing off during specific situations, such as watching TV, sitting and talking to someone, sitting quietly after a lunch without alcohol and stopping briefly in traffic while driving.
Based on the Epworth results, the researchers designated participants as "no dozing" (44 percent), "some dozing" (47 percent) and "significant dozing" (9 percent).
In the two years of follow-up, researchers sought to determine the number of strokes and vascular events -- which they defined as a heart attack or stroke death caused by vascular problems -- among the dozing study members. They detected 40 strokes and 127 vascular events.
After controlling for several stroke risk factors -- age, race-ethnicity, sex, education, blood pressure, diabetes, obesity and physical activity -- they found unexpectedly high stroke risks for the "some dozing" and "significant dozing" groups compared to "no dozing."
The risk of a heart attack or vascular death was higher -- 1.6 percent for the moderate dozers and 2.6 percent for the significant dozers. The findings were similar for all ethnicities and both genders.
"Given what's known now, it's worth assessing patients for sleep problems," Boden-Albala said. "And the initial assessment can be something as simple as the Epworth scale. If patients are moderately or significantly dozing, physicians need to think about sending them for further evaluation."
These findings, if confirmed by other studies, carry important public health implications as well.
"Studies demonstrate that we are not getting enough sleep, so we're tired," Boden-Albala said. "But the real question is, what are we doing to our bodies? Sleepiness obviously puts us at risk of stroke."
Co-authors are Carl Bazil, M.D.; Yeseon Moon, M.S.; Janet De Rosa, M.P.H.; Mitchell S. Elkind, M.C.; Myunghee C. Paik, Ph.D.; and Ralph L. Sacco, M.D.
The National Institute of Neurological Disorders and Stroke funds the NOMAS study.
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