Excess weight increases stroke risk, a new study including nearly 2.3 million people confirms. And the heavier a person is, the greater their risk.

“Being obese (but indeed even just overweight) puts an individual at significantly higher risk of ischemic stroke, with a serious possibility of permanent disability and reduced life expectancy,” Dr. Pasquale Strazzullo of Frederico II University of Naples Medical School in Naples, Italy, one of the study’s authors, told Reuters Health.

Ischemic strokes occur when blood vessels supplying the brain are blocked. Hemorrhagic strokes, caused by bleeding in the brain, are less common.

While being overweight increases a person’s likelihood of having stroke risk factors such as high blood pressure, the question of whether being overweight or obese directly ups stroke risk has not been answered adequately; evidence from past research has been “controversial,” Strazzullo noted.

To investigate, he and his colleagues searched the medical literature for studies with at least four years of follow-up that looked at stroke risk based on body mass index, or BMI, a standard measure of weight in relation to height used to gauge how fat or thin a person is. They found 25 studies including 2,274,961 people, who had a total of 30,757 strokes.

People who were overweight were 22 percent more likely to suffer an ischemic stroke than normal weight people, while the risk for obese people was 64 percent higher, the researchers found. Hemorrhagic stroke risk wasn’t higher for overweight people, but it was 24 percent higher for obese people.

A person’s risk of having a stroke within the next 10 years can be estimated based on their gender, blood pressure, whether or not they smoke, and whether or not they have diabetes, Strazullo explained.

For example, a 62-year-old man whose systolic blood pressure (the top number) is 125, doesn’t smoke, and does not have diabetes or other cardiovascular problems, would have a 4 percent risk of stroke over the following decade; if the same man had a systolic blood pressure of 160 (140 and above is too high) and wasn’t receiving treatment for high blood pressure, his risk of stroke within the next 10 years would be 15 percent.

Therefore, obesity would raise the risk of stroke to nearly 6 percent for the man with normal blood pressure, and to 25 percent for the man with untreated high blood pressure.

Strazzullo and his team also found that once they accounted for lifestyle risk factors like smoking, age, and cardiovascular risk factors, overweight and obesity independently affected stroke risk. One possible reason for this, the researcher noted, is that fat cells secrete several substances that have “unfavorable effects” on the body, for example promoting inflammation, hardening of the arteries, or blood clotting.

Given the difficulty of treating obesity, the researcher said, the best approach to preventing related complications like stroke is for people to avoid packing on the pounds in the first place.

“All of us should keep tight control of our weight and take immediate action in case of weight gain, reducing calories and increasing physical exercise,” he advised.

SOURCE: Stroke, April 2010.