"In the over-70 age group, overall obesity did not predict heart attack risk," said Barbara J. Nicklas, Ph.D., lead researcher. "It didn't matter how much fat the older woman had – what mattered was where that fat was stored."
The researchers found that intra-abdominal fat, or fat stored in and around the internal organs, is most predictive of heart attack risk. The results are reported in the current issue of the American Journal of Epidemiology.
"People with higher levels of intra-abdominal fat tend to be apple-shaped rather than pear-shaped" Nicklas said. "As we age, fat gets stored in the abdomen more than anywhere else, which isn't good because it's now associated with heart attacks. The best way to lose that fat is to lose overall body fat through exercise and diet."
The study was conducted in initially healthy 70- to 79-year-old men and women from Pittsburgh, Pa., and Memphis, Tenn., who were enrolled in the Health, Aging and Body Composition (Health ABC) Study. Individuals were eligible for the study if they reported no life-threatening illness such as heart disease, as well as no difficulty walking a quarter of a mile, climbing 10 steps or performing basic activities of daily living.
At the beginning of the study, the researchers measured total body fat as well as fat distribution (waist-to-thigh ratio, waist circumference, and intra-abdominal or visceral fat). Participants were contacted every six months for the next 4½ years to collect data about hospitalizations or major outpatient procedures for heart attack.
The research revealed that intra-abdominal fat was a risk factor even if women did not have any other risk factors for heart disease. "Women who had a heart attack during the course of the study had approximately 27 percent more intra-abdominal fat at the start of the study," said Nicklas. "This risk factor was independent of total amount of body fat, diabetes, blood pressure and blood lipid levels."
One surprising finding from the study was that intra-abdominal fat was not a predictor of heart attack in men ages 70 to 79. "None of the body fat measures were predictors of heart attack in men," said Nicklas. "My theory is that men who had high levels of fat would have experienced heart disease earlier than in their 70s; therefore, they weren't eligible for our study. I wouldn't be surprised if we did a study of men in their 50s and 60s in which we would see abdominal fat as a strong risk factor for a future heart attack."
Knowing more about intra-abdominal fat as a risk factor for heart disease could lead to early screening, said Nicklas. Waist size is one easy way to screen but, according to the study results, may not be the most accurate.
"There are clinically defined cut-points for waist size --35 inches for women and 40 inches for men--that suggest a person is at higher risk for heart disease," Nicklas said. "However, in this study, waist size was not an accurate predictor of heart attack."
The most accurate method for measuring intra-abdominal fat is the more expensive computed tomography (CT) scan. "From the scan, we could determine how much abdominal fat was stored just underneath the skin versus how much was stored in the abdominal cavity, or inside the muscle wall," Nicklas said.
The research was funded by grants from the National Institute on Aging, including the Wake Forest University Claude D. Pepper Older Americans Independence Center. Nicklas' co-researchers were Brenda Penninx, Ph.D, Matteo Cesari, M.D., Ph. D., Stephen B. Kritchevsky, Ph.D., Jingzhong Ding, Ph.D., and Marco Pahor, M.D., all from Wake Forest Baptist, Anne B. Newman, M.D., from the University of Pittsburgh, Alka M. Kanaya, M.D., from the University of California at San Francisco, and Tamara Harris, M.D., from the National Institutes of Health.
Contacts: Karen Richardson, krchrdsn@wfubmc.edu; Shannon Koontz, shkoontz@wfubmc.edu; at 336-716-4587.
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Journal
American Journal of Epidemiology