BMI doesn't measure up for seniors
SCOTT ROBERTS
Globe and Mail Update
When determining death risk among seniors, it seems the size of their pants may be a better indicator than their weight, according to a new study.
Researchers at the London School of Hygiene and Tropical Medicine have found that body mass index, a measure of body fat based on height and weight, is a poor indicator of health in men and women over 75 because it doesn't differentiate between fat and other tissue like bone and muscle, which is progressively lost with age.
Instead, they say the waist-to-hip-ratio of a senior should be the gold standard in measuring mortality risk because it takes into account body shape and composition. Waist-to-hip ratio is found by dividing the size of a person's waist by the size of their hips.
The results of the study don't surprise University of Guelph professor Heather Keller.
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“With body mass index we don't know what the weight represents,” said Dr. Keller, who specializes in geriatric nutrition. “What we do know is that fat mass, especially around the abdomen, is an important to health risk. And this is why waist circumference itself or waist-to-hip ratio might be better because it really measures the key thing, which is fat in the abdomen.”
The report, published in Tuesday's American Journal of Clinical Nutrition, studied 14,833 patients over the age of 75 and found BMI overestimates the risk of excess weight in older people and that seniors with a low BMI, essentially underweight, are more at risk of dying.
The findings are in step with previous studies that suggest seniors that are overweight but not obese do not face increased health risks.
“There have been several studies that say a higher BMI isn't as detrimental to health for older people as it is for younger people,” said Dr. Keller. “As long as you have a BMI under 30 you're not having any increased health risks if you're over 65.”
The new study comes on the heels of similar research criticizing BMI as an accurate indicator of poor health. In 2003, Australian researchers found that waist-to-hip ratio was much more accurate in determining obesity than BMI. And last November, Canadian researchers found that waist-to-hip ratio was three times better at predicting heart attacks than BMI.
The authors of the study said that although health risks associated with a high BMI decline with age, many organizations use the same criteria for all age groups. As a result, they're calling on health officials to cease using BMI as an indicator of death risk in seniors and instead adopt the waist-to-hip ratio.
The Canadian Guidelines for Body Weight Classification recommend that doctors measure a patient's waist in addition to their weight to help determine any health risks.
But Dr. Keller said waist-to-hip ratio is not usually measured by doctors in Canada.
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