The most frequently used measurement for body fat, a formula known as body mass index (BMI), may not be the most accurate way to calculate disease risk, most specifically the risks of certain cancers, according to a new study in American Journal of Epidemiology.

BMI is figured by dividing a person’s weight (in kilograms) by his or her height in meters squared. Studies started using this formula 60 years ago among middle-aged men.

Recently it has become the most frequently used weight-for-height index in big population research measuring children and adults. It is easily calculated because of the readily available height and weight data. Other ways to measure body fat have proved to be time consuming and costly.

Obesity is interpreted as a BMI of 30 or higher, while an ideal BMI is considered to be between 18.5 and 24.9. The higher the BMI, the greater the risk for a variety of diseases, like heart disease, type 2 diabetes, high blood pressure, and certain cancers, as stated by the Centers for Disease Control and Prevention.

A previous study done by the University of Manchester has suggested a higher BMI is associated with a great risk of certain cancers. They also discovered a weaker link between BMI and risk of malignant melaleukaemia, multiple myeloma, and non-Hodgkin lymphoma in both men and women.

A separate study suggests BMI as a predictor for breast cancer survival. Women who underwent surgery and had a normal BMI had a longer, overall disease-free survival than obese women with a high BMI.

Lead author Geoffrey C. Kabat, Ph.D., senior epidemiologist in the department of epidemiology & population health at Albert Einstein College of Medicine of Yeshiva University, says:

“It has long been recognized that BMI is an imperfect indicator of body fat because weight does not distinguish between lean body mass (muscle, bones, blood, water) and fat mass. This means that two individuals can have the same BMI but can have very different percentage of body fat. Furthermore, when using weight and height data, a single BMI formula may not be appropriate for all populations and all diseases.”

The current study aimed to identify whether alternative weight-for-height measures end in more significant associations with risk of certain cancers compared with BMI.

Looking at data from 90,000 Canadian women, who were enrolled in the Canadian National Breast Screening Study, the researchers altered the BMI formula by changing the value of x in W/Hx. This modification was used to determine whether these variations on BMI better predict the risk of 19 different cancers.

All values of x in W/Hx that showed meaningful associations with certain cancers were less than the value of 2.0 (i.e. BMI) and included 1.7 for postmenopausal breast cancer, 1.3 for lung cancer in non-smokers, and 0.8 for endometrial cancer.

These conclusions will need to be verified in other studies. The authors believe the ideal value of W/Hx may vary in different populations as well as with each disease being investigated. They suggest BMI may not be best for all purposes.

Written by Kelly Fitzgerald