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High rate noted particularly among blacks may be due to genetic factors, researcher says
The greater your body weight is, the higher your chances of having a stroke, according to a recent study.
For the current study which involved monitoring of 13,549 middle-aged Americans for a period of 19 years, researchers examined risk of stroke linked to a number of obesity measures, giving emphasis on body mass index (BMI), a ratio of weight and height, but also other measures like waist circumference.
Lead author Dr. Hiroshi Yatsuya, a visiting associate professor of public health at the University of Minnesota, wrote in their report that they discovered that "the risk of stroke was increased with each measure of obesity." The report was published in the online issue of Stroke, dated Jan. 21.
The degree of risk was found to vary according to sex and ethnic group. For instance, people belonging to the highest BMI category had 1.43 to 2.12 times higher risk of having a stroke, with differences by race and sex. When waist circumference was used to measure obesity, the risk ratios were from 1.65 to 3.19 and from 1.69 to 2.55 when the waist to hip ratio was used.
The study found that blacks were specifically at higher risk. For instance, compared with 1.2 per 1,000 person-years for white women, the rate of stroke for black women was 4.3 per 1,000person-years. In the highest category for BMI, incidence rates ranged from 2.2 for white women to 8.0 for black men.
According to Yatsuya, that higher rate of stroke for blacks has been observed in many studies in the past, and that it is also noted in Asians. He said that that while the reason remains unknown, a "genetic difference" may be present.
However, the study found that the higher risk associated with body weight was noticeable in every ethnic origin. Across ethnic groups, men and women under the highest obesity category had approximately two times the risk for stroke as did study participants belonging to the lowest category.
The findings of the study showed that obesity seems to work by causing an increase in the incidence of high blood pressure and diabetes, two key risk factors for stroke and cardiovascular disorders. When blood pressure measurements and diabetes were accounted for in the calculations, the link between obesity was undermined, indicating that these key risk factors provide much explanation of the association between obesity and stroke, Yatsuya said.
In spite of the body of evidence associating obesity with stroke, Yatsuya said that they do not have apparent proof that reduction of obesity lowers the incidence of stroke. To provide evidence that prevention or reduction of obesity decreases the risk of stroke, controlled trials are essential.
The American Heart Association spokesperson Daniel Lackland, a professor of epidemiology at the Medical University of South Carolina, said that the precise nature of the relationship between obesity and risk of stroke has not been ascertained, however, the new study adds to a clearer understanding of it.
Lackland said that obesity plays a contributory role to both diabetes and hypertension or high blood pressure, which are linked to stroke and at a younger age.
Despite the apparent lack of conclusive evidence proving that prevention or reduction of obesity lowers the risk of stroke, the American Heart Association and other major organizations give emphasis on the need to control weight by adopting a healthy diet and engaging in physical activity, he said.
A BMI of 20 is considered normal, while a BMI ranging from 25 to 29 is regarded as overweight, a reading of 30 indicates obesity.
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