Women who are obese or who gain significant amounts of weight as adults have a higher risk of the most common kind of stroke, according to a study in tomorrow's issue of The Journal of the American Medical Association. The new finding, says study author Kathryn Rexrode of Brigham and Women's Hospital in Boston, is the first strong indication that obesity is a significant risk factor for stroke.
Obesity has long been associated with heart disease, but the connection to strokes has been unclear. One reason, says epidemiologist Rexrode, is that until recently it was difficult to distinguish between the two main types of stroke: ischemic and hemorrhagic. Ischemic strokes, which account for about 80% of all strokes, occur when a blood clot blocks a vessel in the brain, reducing blood flow. Hemorrhagic strokes result from blood vessels that burst. Advances in brain imaging have allowed doctors to better diagnose stroke types, and so Rexrode and her colleagues decided to see whether obesity might be correlated with one type of stroke but not the other.
They used data amassed during the Nurse's Health study, which collected a wide variety of health information from middle-aged women between 1976 and 1992. The researchers looked at data on more than 116,000 women who had not been diagnosed with heart disease, stroke, or cancer at the beginning of the 16-year study. They found that women who had a body mass index--weight in kilograms divided by height in meters squared--of 32 or more had more than twice the risk of ischemic stroke than did women with BMIs below 21. Women who gained significant amounts of weight as adults--between 10 and 20 kilograms since the age of 18--had nearly twice the risk of ischemic stroke, while those who gained 20 kilograms or more had more than two and a half times the risk of women who maintained a stable weight.
But added weight did not increase a woman's risk of the more deadly, but less common, hemorrhagic stroke. In fact, the risk of hemorrhagic stroke was higher for women with lower body mass index, but that may be because they were more likely to smoke--a strong risk factor for hemorrhagic stroke.
The increased risk seems to be connected to side effects of obesity such as high blood pressure, diabetes, and high cholesterol levels, which are known stroke risk factors. The study "reinforces what we have suspected about obesity," says neurologist John Marler of the National Institute of Neurological Disorders and Stroke, but "now I would be more confident telling a patient that losing weight alone could lower risk."