Body Mass Index is not the perfect measurement

One of the measurements that is used in most research regarding common health problems is the Body Mass Index. BMI works as a good guide for us because it is an inexpensive way to evaluate body fat. It is not perfect, however, and use of Waist to Hip Ratio (WHR) is being studied more and more as another measure to help guide both research and therapy in medicine today.

One area in question is the use of BMI in those over 75 years old. There has been the observation that the measurement doesn't appear to correlate as well with disease as with the predictive value it offers in younger people. Gill M. Price and his colleagues in England evaluated whether WHR might be a better way to evaluate the elderly. Dr. Price's reports on data collected from almost 15,000 participants of a study in the U.K. (AJCN 2006;84(2):449-460).

Height, weight, hip and waist measurements, as well as a wide range of lifestyle, physical and social information, was collected as part of a large multi-center effort beginning in the early 1990s and extending into 2003. The researchers found that those over 75 with higher BMI were not necessarily at higher risk for dying from cardiovascular problems or many other health issues.

Interestingly, a higher WHR was positively associated with such health issues as well as death from circulatory illness (heart attack and stroke). This was not true when the researchers looked at the measurement of the waist by itself, however.

While it is a good and inexpensive assessment of body fat there are limitations to using BMI. Measuring the WHR helps to define what is known as "central adiposity" or fat around one's middle (that "spare tire" many develop in middle age). The elderly often lose muscle mass before losing the spare tire and the result can be a skewed BMI. Likewise, any loss of height as people age (which is common) will alter the BMI equation as well.

What this means for you:

In my practice I use both BMI and WHR to evaluate patient's potential problems with weight at every age. Neither is a perfect measurement and as with all such tests must be taken in context of the individual.

First posted: August 16, 2006