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15-12-2009 | Diabetes | Article

BMI more important than physical activity in determining diabetes risk


Free abstract

MedWire News: Body mass index (BMI) is a major determinant of Type 2 diabetes risk while physical activity has only a modest influence, 20-year data from the Physicians’ Health Study reveal.

The findings support the importance of maintaining a normal BMI, since once overweight or obesity had occurred, increasing amounts of vigorous activity were required to offset the associated diabetes risk.

“There is now a growing awareness of the importance of analyzing joint effects of BMI and activity as related to measures of health status and morbidity,” remark Lydia Siegel (Brigham and Women’s Hospital, Boston, Massachusetts, USA) and co-authors.

The researchers therefore examined individual and joint associations among activity, BMI, and the risk for Type 2 diabetes in 20,757 middle-aged and older men followed-up for a median of 23.1 years. They were participating in the Physicians’ Health Study, a longitudinal study of men aged 40–84 years and free of diabetes at baseline.

There were 1836 new cases of diabetes during follow-up, Siegel’s team reports in the American Journal of Medicine.

The diabetes incidence rate rose with increasing BMI at baseline, at 2.4, 6.1, and 153.0 per 1000 person-years for men who were normal-weight, overweight, and obese, respectively.

Conversely, the incidence rate declined with increasing physical activity at baseline, at 6.5, 5.1, 4.7, 3.7, and 2.8 per 1000 person-years for men who were rarely or never active, active one-to-three times per month, active once a week, active two-to-four times weekly, and active five or more times weekly, respectively.

Interestingly, BMI and physical activity interacted with respect to diabetes risk. Compared with active men with normal BMIs, physically active but overweight and obese men had multivariable-adjusted hazard ratios (HRs) of 2.39 and 6.22, respectively, while inactive men with normal, overweight, or obese BMIs had multivariable-adjusted HRs of 1.41, 3.14, and 6.57.

Furthermore, among normal-weight and overweight or obese individuals, any amount of physical activity was associated with a reduced risk for diabetes compared with weight-matched inactive men.

Among obese men, by contrast, only those who were physically active five or more times weekly had a significantly lower risk for diabetes than their inactive counterparts. Only 9.2% of obese men attained this level of activity, the authors remark.

“Our data underscore the importance of focusing on the combined relationships among physical activity, BMI, and diabetes,” write Siegel and co-authors.

“These data are clinically useful as further evidence in men that the diabetes risk associated with a high BMI can be moderately attenuated by vigorous activity, but that the most protective clinical feature is a normal BMI.”

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2009

By Joanna Lyford