No matter how you measure obesity — by body-mass index (BMI), waist circumference or waist-to-hip ratio — being obese raises your risk of stroke.
And, regardless of race or gender, the more obese you are, the greater your risk.
The study also found that the incidence rate of stroke among obese blacks is higher than that among obese whites.
“It’s not clear yet what is causing those [stroke risk] differences in races,” said Hiroshi Yatsuya, MD, PhD, the study’s lead author and a visiting associate professor at the University of Minnesota, in a phone interview.
Genetics, lifestyle (dietary and exercising) habits, and socioeconomic status (which affects access to good healthcare) could all play a role, he said.
A widespread worry
Stroke is the third leading cause of death in the United States. It’s also the leading cause of serious, long-term disability. About 55,000 more women than men have strokes each year. Blacks are twice as likely as whites to have a stroke, and their outcomes tend to be worse.
High blood pressure, diabetes and smoking are well established as risk factors for stroke, but the evidence linking being overweight with a higher risk of stroke has been more muddled.
In addition, there’s been a growing dispute among clinicians about which way of measuring fat is most accurate for determining disease risk. Some have argued that BMI, which can be high in non-obese but muscular people, is a poor measurement tool.
The study in detail
The current study used data on more than 13,000 middle-aged black and white participants in the government-sponsored Atherosclerosis Risk in Communities (ARIC) Study. Participants were drawn from four U.S. population pools, which included the northwest suburbs of Minneapolis as well as communities in North Carolina, Mississippi and Maryland. All were free of cancer and cardiovascular disease when the study began. All also had their BMI, waist circumference and waist-to-hip ratio measured at the study’s start.
During the study’s 19 years of follow-up (1987 to 2005), 598 people had ischemic strokes (the most common kind of stroke, caused when a blood clot or other obstruction blocks an artery to the brain). After crunching the numbers, Yatsuya and his colleagues found a significant difference in incidence rates between black and white participants in the study.
Black women, for example, were about three times more likely to experience a stroke than their white peers in both the lowest and the highest BMI categories.
But people of both races and genders were more likely to have a stroke as they became more obese, Yatsuya said. Although it varied a bit by race and sex, the stroke risk for people in the highest BMI category was 1.43 to 2.12 times higher than for those in the lowest BMI category.
And the findings were similar when obesity was measured by waist circumference and waist-to-hip ratio. For example, the overall stroke risk for people in the highest category of waist-to-hip ratio was 1.69 to 2.55 times higher than for those in the lowest waist-to-hip ratio category.
Of course, people with higher levels of obesity are more likely to have high blood pressure and diabetes — two of the known risk factors for stroke. And, indeed, when Yatsuya and his team adjusted for these factors, they found that the association between stroke and obesity weakened.
Yatsuay said these risk factors could explain the obesity-stroke correlation that he and his colleagues found.
The next step? “We now need a clinical trial to see whether obesity prevention or control would decrease the incidence of stroke,” he said.