The more overweight people become, the more likely they are to have a heart attack or stroke and to develop risk factors for heart disease like high blood pressure, a large UK study concludes.
Contrary to some past research suggesting there might be a heart-protective effect of being overweight or obese, the study team found the opposite, according to their report in the European Heart Journal.
Researchers examined data on more than 296,000 middle-aged men and women without heart disease, many of whom were overweight or obese based on their body mass index (BMI) - a ratio of weight to height. After an average follow-up of five years, 3.3 percent of the women and 5.7 percent of the men had a heart attack, stroke or other serious cardiovascular event.
Compared to a BMI of 22, which falls within a healthy weight range, each 5.2-point increase in BMI for women and each 4.3-point BMI increase for men was associated with a 13 percent higher risk of events like heart attacks or strokes during the study period. With BMI increases of that magnitude, many people might shift from a healthy weight to overweight, or from overweight to obese.
"You can be relatively healthy as overweight or obese but you will still have a greater risk of cardiovascular disease compared with the normal BMI individuals that have exactly the same profile in the other risk factors," said lead author Stamatina Iliodromiti of the University of Glasgow.
"Some studies have suggested that obesity may be protective against cardiovascular disease," Iliodromiti said by email. "We did not directly tackle the 'fat but fit' problem, but we showed that the greater the adiposity, either measured as total body fat or fat around the abdomen, the greater the risk of cardiovascular disease, irrespective of other conventional risk factors like inactivity or (low) socioeconomic status."
Some recent research has suggested that overweight people may live longer than their normal-weight counterparts, a phenomenon often described as the "obesity paradox." Much of this research didn't account for other measures of body composition in addition to BMI, the study team argues.
The current study also looked at waist circumference, the size of the hips relative to the waist, and body fat percentage. All these measurements are used to gauge the amount of total fat a person carries, or adiposity.
Among women with a BMI of 22, for example, each 12.6 centimeter (5 inch) increase in waist circumference beyond 74 centimeters (about 29 inches) was associated with a 16 percent higher risk of cardiovascular disease, the study found.
And for men with a BMI of 22, each 11.4 centimeter (4.5 inch)increase in waist circumference beyond 83 centimeters (almost 33 inches)was associated with a 10 percent higher risk of cardiovascular disease.
Increases in waist-to-hip ratio and body fat percentage were also associated with a greater risk of developing cardiovascular disease.
The study wasn't a controlled experiment designed to prove whether or how weight or body fat might directly cause heart disease.
Still, the results add to evidence linking obesity to an increased risk of heart disease and offer fresh insight into the limitations of looking only at BMI to assess obesity, said Trine Moholdt, a researcher at the Norwegian University of Science and Technology who wasn't involved in the study.
BMI is imperfect because it doesn't distinguish between body fat and lean muscle mass, Moholdt said by email.
"In many people who are overweight or obese, BMI can help target a healthier weight or BMI goal; however, just because they get to the 'normal' range doesn’t necessarily mean they have maximally lowered their risk," said Dr. Michael Hall, a researcher at the University of Mississippi Medical Center in Jackson who wasn't involved in the study.
"Certainly, increasing physical activity can have benefits beyond weight so this is very important," Hall said by email. "The take home message should be avoid excess weight and exercise regularly."
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