Obesity nearly doubles the risk that an otherwise healthy middle-aged man will eventually have a stroke, a long-running Swedish study finds.

The researchers followed more than 7,400 men aged 47 to 55 for 28 years and discovered that a man with a body mass index (BMI) of more than 30 was 93 percent more likely to have a stroke than one with a healthy BMI of between 20 and 23, said a report in the Oct. 29 issue of Stroke.

That increased risk was present even when known stroke risk factors such as diabetes, high blood pressure, and high cholesterol were taken into account, said study author Dr. Katarina Jood, a research fellow at Sahlgrenska University Hospital in Goteborg.

BMI is an individual's weight in kilograms divided by the square of height in meters. Someone with a BMI of 25 is classified as overweight, and obesity is marked by a BMI of 30 of higher.

High blood pressure (hypertension) remains the leading risk factor for stroke, Jood said. "However, it is always difficult to rank the risk factors, and by saying that hypertension is the most important risk factor does not mean that obesity is unimportant," she added.

Other large-scale studies have found a similar link between obesity and stroke risk. Notably, a report in 2002 by physicians at Brigham and Women's Hospital in Boston on the 21,000-man Physicians Health Study gave a precise numerical relationship: a one-unit increase in BMI raised the risk of stroke by 6 percent.

A one-unit BMI increase would be a weight gain of 7.4 pounds for a 6-foot-tall person and 6.2 pounds for someone 5 feet, 6 inches.

The value of the latest study is that it followed participants for a more prolonged period than any other trial, said Dr. Lawrence M. Brass, a professor of neurology at Yale University and a spokesman for the American Heart Association.

"It is a really potent effort to be able to say to a 40-year-old man that what you are doing now will affect your risk when you are 70," Brass said. "Small changes in BMI may lead to huge advantages in stroke prevention down the line."

The study was not designed to determine the mechanism by which obesity leads to stroke, Jood said. But obesity is associated with insulin resistance, inflammation and other factors that increase risk, she noted.

Determining the mechanism is a challenge, Brass said. "The two most likely mechanisms are increased insulin resistance and disordered breathing," he said. "Both those things are eminently treatable."

Losing weight would seem an obvious way to reduce risk, but "it is not possible to make any conclusion about the effect of weight reduction from our study, as there was no intervention directed toward obesity," Jood said.

And weight reduction is a major medical challenge, Brass said. "If we could figure out how to help people lose weight. . ." he mused. "There are some interesting medications to alter body-mass index in trials."

More information

The facts about obesity and the various cardiovascular problems it causes can be found at the American Heart Association.

Reference Source 101
October 29, 2004

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