MAY 2010

After age 70, a few extra pounds may not be so bad. New Australian research adds to the evidence suggesting that the rules about weight and health are different for older people— and that Body Mass Index (BMI) isn’t a perfect tool. The study of 9,240 men and women ages 70 to 75 found that being overweight was associated with a 13% lower risk of mortality from all causes. Normal-weight and obese participants had a similar, slightly higher risk of death from all causes.

Leon Flicker, PhD, of the Western Australia Center for Health and Aging, and colleagues looked at data from two long-running studies, the Health in Men Study and the Australian Longi - tudinal Study of Women’s Health, both with about 10 years of follow-up. They used self-reported height and weight to calculate BMI, and the criteria set by the World Health Organization (WHO) to characterize body weight:
• Under 18.5 BMI = underweight
• 18.5-24.9 = normal weight
• 25-29.9 = overweight
• Greater than 30 = obese.

These thresholds, Flicker and colleagues pointed out, were originally developed based primarily on studies of younger and middle-aged adults.

Hardly any of the participants were underweight, while 44.3% of the men and 33.5% of the women were overweight; 11% of men and 13.1% of women were obese. Australia ranks third in the world in obesity, behind only the US and the UK.

Publishing their findings in the Journal of the American Geriatrics Society, the researchers concluded, “Even after removing the effects of early mortality, those who were overweight were still at lowest risk, a finding consistent with the observation that weight loss in older age is associated with greater mortality.… These results lend further credence to claims that the BMI thresholds for overweight and obese are overly restrictive for older people.”

Don’t take the findings as a license to loaf on the couch, however: A selfdescribed sedentary lifestyle doubled mortality risk for women and boosted it by 28% for men.

This study isn’t the first to raise questions about the usefulness of BMI— a simple equation linking height with weight (weight in kilograms divided by height in centimeters squared)— as an indicator of overall health. Back in 1985, Reubin Andres, PhD, of the National Institute on Aging and colleagues published a study in the Annals of Internal Medicine based on insurance actuarial data that showed the “ideal” BMI—defined as lowest risk for chronic disease or mortality— increasing with age. For twentysomethings, a BMI of 21.4 for men and 19.5 for women was ideal. By ages 60-69, however, the BMI associated with lowest risk had risen to 26.6 for men and 27.3 for women—figures deemed overweight by the WHO criteria. For ages 70-79, the ideal BMI was 27 for men and 27.8 for women.

Such findings fit with common sense: Who hasn’t seen rail-thin elderly, so frail that a bout with a disease such as pneumonia taxes their ability to survive?

Indeed, a study published in Obesity in 2005 looked at 12 years of data on more than 11,000 Canadians and found that underweight adults had a 73% greater mortality risk compared to those of normal weight. The overweight, however, were at 17% lesser risk. Similarly, in a controversial 2007 study, researchers at the US Centers for Disease Control and Prevention (CDC) and the National Cancer Institute concluded that overweight adults were less likely to die of a range of diseases, including infection, lung disease and Alzheimer’s.

Remember, too, that BMI doesn’t measure only body fat; it’s high body fat, not weight per se, that endangers your health. Plus, muscle weighs more than fat—one reason many pro football players are technically “obese.” Nor does BMI account for the distribution of body fat: Research has shown that potbellied people (“apple-shaped”) who store their fat above the hips are at greater risk for heart disease, diabetes and other chronic health problems than “pear-shaped” people who are fatter below the hips. These issues with BMI lead many experts to argue that waist-hip ratio is a better measure of weight and health risk.

The investigators in the latest study didn’t explain why a little extra weight might be protective. But in an interview, Flicker theorized: “We can only hypothesize, but it may be that as we age, the presence of nutritional and metabolic reserves [e.g. fat] is advantageous. If you develop an illness, a little more reserve gives you a greater chance to recover from that illness.”

Flicker and colleagues cautioned that the participants in the studies they analyzed had a lower overall mortality rate than the general population, suggesting they were healthier to begin with. And of course they had to survive to age 70 to be included: People who died of obesity-related illnesses at a younger age didn’t make the study.

Flicker added, “The situation is slightly different for older people with specific diseases like diabetes mellitus or severe hip or knee osteoarthritis, where some weight loss may be symptomatically beneficial.”

For “successful agers” who do make it to 70, however, you can probably pitch the dieting books if you’re only a little overweight. “Our study suggests that those people who survive to age 70 in reasonable health have a different set of risks and benefits associated with the amount of body fat, compared to younger people,” Flicker said. “Over weight older people are not at greater mortality risk, and there is little evidence that dieting in this age group confers any benefit.”

TO LEARN MORE: Journal of the American Geriatrics Society, February 2010; abstract at dx.doi.org/ 10.1111/j.1532-5415.2009.02677.x. NHLBI Obesity Education Initiative www.nhlbisupport.com/bmi.