What Are Excess BMI Years?

September 12th, 2011 by Ryan Luce No Comments

written by Michael O’Leary

Much like smoking, the length of time people are overweight the greater their risk of developing type 2 diabetes, a new study shows.

In the study, researchers found that in a group of 40-year-old adults with excess BMI-years (body mass index) of 200 years had three times the risk of developing type 2 diabetes as similar adults with only 100 years of excess BMI.

Excess BMI-years is calculated by the number of points above BMI of 25 multiplied by the number of years the person maintained that BMI. For example a person with a BMI of 35 (10 points higher than healthy weight) for 20 years would be considered to have 200 years of excess BMI. A healthy BMI is considered to be between 18.5 and 24.9. (Link to published site)

The study reported on by the Los Angeles Times appeared online this week in the journal Archives of Pediatrics & Adolescent Medicine. In it, researchers led by Dr. Joyce Lee, of the Division of Pediatric Endocrinology at the University of Michigan, examined the relationship between excess body mass index and the length of time people carried excess BMI and the occurrence of type 2 diabetes.

“We know that, due to the childhood obesity epidemic, younger generations of Americans are becoming heavier much earlier in life, and are carrying the extra weight for longer periods over their lifetimes,” said lead author Dr. Joyce Lee of Mott Children’s Hospital in a news release. “When you add the findings from this study, rates of diabetes in the United States may rise even higher than previously predicted.”

The researchers followed 8,157 adolescents aged 14-21 into their 40s over a 27-year period from 1979 to 2006.  During that time 337 people developed type 2 diabetes. When they analyzed the length of time participants maintained a BMI of 25 or more they found that white men aged 40 years with 200 excess BMI-years had 2.94 times higher odds of developing diabetes compared with men of the same age and race with 100 excess BMI-years.

The study also showed that blacks and Hispanics compared with white individuals had a higher risk for diabetes. They found that younger men and Hispanic men who had longer duration excess BMI had a higher risk of type 2 diabetes than white people with the same excess BMI over the same length of time.

A major limitation of the study, however, is that the researchers relied on the men to self-report their height, weight and diabetes status between 1981 and 2006. Nevertheless, the study raises an alarm regarding the increasing rates of obesity among children.

“The tripling of obesity rates for US children during the last 30 to 40 years,” they wrote in the study, “implies that younger generations of individuals are carrying a longer duration of obesity over their lifetime.”