BMI standards for younger adults may not be appropriate for people in their 80s and 90s

May 16 2006

If you're more than 80 years old, carrying a few extra pounds might not be such a bad idea. In fact, it may be beneficial.

That's one of the findings from a joint UC Irvine and University of Southern California analysis of body mass index (BMI) and mortality rates from participants of a large-scale study based in a Southern California retirement community.

The analysis found that study participants in their 80s and 90s who were overweight by BMI standards (25 to 29.9 range) had lower mortality rates than those who were in the normal range (18.5 to 24.9). The findings suggest that the BMI scale, which applies to all adults, may not be appropriate for the elderly and should be age-adjusted. This supports other research offering the same conclusion. The study appears in the May 15 issue of the American Journal of Epidemiology.

"We found that what's recommended for everyone else with body mass index measurements isn't necessarily the best for the elderly," says Maria Corrada, an epidemiologist in the UCI School of Medicine who led the analysis effort. "It seems that if you're in your 80s or 90s, you may live even longer if you are a bit overweight by BMI standards."

The study, which is part of the Leisure World Cohort Study at Laguna Woods, Calif., looked at survey data taken from 13,451 residents in the large retirement community in 1981-83 and 1985. The residents, whose average age was 73 at the time of the survey, provided their height and weight at age 21 and at the time of the survey.

In addition to finding that those who were overweight had the lowest mortality rates, the researchers discovered:

• People who were underweight at the time of the survey (BMI below 18.5) had the highest mortality rates, even higher than those who were obese (BMI 30 and higher).
• People who were either overweight or obese at age 21 had increased mortality rates. This held true even if they lost the weight by the time of the survey.
• People who lost weight between age 21 and late adulthood had increased mortality regardless of their weight at age 21.

"What's interesting about these findings is that is supports previous studies that recommend people to stay in the 'normal' BMI range during young adulthood and slowly gain weight during their elderly years," Corrada said. "In turn, obesity during young adulthood and being underweight during the elderly years leads to higher mortality rates."

"The overall message," Corrada added, "should be that what constitutes a 'normal' range for people over 80s should be re-examined."