For many years Body Mass Index, or BMI, has been the go-to index for establishing trends in population weights, and has also been used to establish what are the best BMIs to avoid certain ailments such as diabetes as well as early death. It has been widely accepted that the relationship of BMI and risk of death, or mortality, is J- or U-shaped. That is, the risk of death is lowest at an intermediate value of BMI not at the lowest BMI seen in healthy adults. For years, experts have widely accepted that this ideal BMI value is similar for men and for women, and for all adults. A report published in the American Journal of Clinical Nutrition by several Australian researchers challenges this latter assumption, however.
Dr. Jane E. Winter from Deakin University and colleagues from the Cancer Epidemiology Centre and the University of Melbourne, Australia, performed a meta-analysis of 32 studies to determine the association between BMI and all-cause mortality in adults ages 65 years and older. In all, these studies included nearly 198,000 individuals who were followed for an average of 12 years.
The researchers used a BMI of 23.0-23.9 as the reference, since that is the recommended BMI associated with minimal mortality by the World Health Organization (WHO). They found that people whose BMI fell in the range of 20.0-20.9 had a 19 percent increased risk of mortality, and those with a BMI between 21.0 and 21.9 had a 12 percent increased risk.The lowest risk was seen in never smokers at a BMI of 26.0-26.9. At the heavier end of the BMI spectrum, mortality risk only began to increase as BMIs rose over 33 by about 8 percent.
In an accompanying editorial, Dr. John D. Sorkin of the Baltimore VA Medical Center, noted that a more reliable means of investigating this question would have been to directly compare the BMIs at the points of minimal mortality for both younger and older people, rather than use the WHO reference point. However, he also notes that, combined with earlier work, this research demonstrates that the question of whether the ideal BMI changes with age should remain open until further research can clarify the issue.
ACSH s Dr. Ruth Kava concurs, This study certainly calls into question some basic assumptions about what constitutes the best BMI for older people. Hopefully further research will clarify the issue, but in the meantime people over the age of 65 probably shouldn t strive to become as lean as they were in their 20s at least not in order to extend their lives, as certain other conditions (arthritis, for instance) do respond to weight loss.