A team at the Medical College of Wisconsin Injury Research Center in Milwaukee has found that being obese increases male drivers’ risk of dying in a car crash, as does being very slim. However, being moderately overweight might cushion the blow.

They also found that obesity did not affect women’s risk of death from such crashes. Their study appears in the April online issue of the American Journal of Public Health and was funded by the Center for Disease Control and Prevention.

“Men with the highest body mass index (BMI) were at greatest risk for death from front or left-side collisions, especially at high speeds” says lead author Shankuan Zhu, M.D., Ph.D., assistant professor of family & community medicine. “Men with the lowest BMI also had higher death rates than the lowest rates, which were found among overweight, but not obese, men.”

Their findings document another potential major health risk associated with obesity among men, and may have important implications for identifying high-risk drivers and for interventions in areas such as obesity, traffic safety policy, and motor vehicle design.

Motor-vehicle crashes are the leading cause of injury-related death in the United States, taking more than 42,000 lives in 2002. The current Federal Motor Vehicle Safety Standards provide protection primarily for the mid-size male (BMI = 24.3 kg/m2). This standard may apply to fewer people now. During the last two decades, more Americans have become obese or extremely obese. A study conducted in 2000 reported that 30.4 percent of American adults have a BMI of 30 or greater and 4.9 percent have a BMI of 40 or greater.

The researchers suggest that the unexplained reasons for the gender difference in BMI and motor vehicle fatality might be, in part, the difference in body habitus or body shape between men and women, and should be studied further. Their findings may also lend credence to the theory of a “cushioning effect” for slightly overweight men that might protect them from fatal injury in a crash, according to Dr. Zhu.

The team studied more than 22,000 drivers, ages 16 and older, using data collected from 1997 to 2001 by the National Automotive Sampling System, Crashworthiness Data System, a data collection system sponsored by the U.S. Department of Transportation.