Living longer with an ideal BMI

Maintaining a healthy body mass index, or BMI, is one of the most important ways to help you live longer, according to a new study published in the December issue of New England Journal of Medicine.

BMI is not a perfect measure, but it is one of the simplest for estimating body weight. It is calculated by weight in pounds divided by height in inches squared and multiplying the number by 703, or by weight in kilograms divided by height in inches squared. What’s your BMI? Find out using this free calculator provided by the National Heart Lung and Blood Institute, of the National Institutes of Health.

The study’s findings support an optimal BMI in the “normal weight” range of 20 to 24.9, which is generally associated with the lowest risk of death from all causes including chronic diseases such as cardiovascular disease and cancer. The association was strongest among participants who were younger than 50 years old.

A BMI of 25 or more was associated with the highest mortality risks. The higher the BMI, the higher the likelihood of dying from cardiovascular disease.

“The results of our analysis are most relevant to whites living in affluent countries,” write the authors who pooled and analyzed data from 19 prospective studies encompassing 1.4 million white adults ages 19 to 80.

In the United States, among non-Hispanic whites, there was an estimated 11 percent of men and 17 percent of women with a BMI of 35 or higher in 2008.

The authors restricted the study to non-Hispanic whites based on self-reported ethnic group and controlled for pre-existing conditions, alcohol consumption, barbital status, education, and physical activity. They also excluded those with a BMI of less than 15 or higher than 50.

Smokers made up 25 percent of the study participants in the lowest BMI category of 15 to 18.4 and 8 percent of those in the highest BMI category.

Source: Berrington de Gonzalez A, Hartge P, Cerhan JR et al. Body-Mass Index and Mortality among 1.46 Million White Adults. NEJM 2010;363:2211-9.

Thoughts:

BMI is easy for anyone to measure, so this study gives us some back-up for using it as a way to speak to clients about real implications of obesity causing a shortened lifespan because of increased risk of cardiovascular disease and cancer.

It's important, however, to realize that while BMI may be easy it's possible for someone to be at a "normal weight" and still be "obese" -- dubbed normal weight obesity. This is still hazardous to your health, so you can't completely rely on BMI. Opt instead for body fat percentage measurement.