Obesity not only puts people at risk for a number of chronic conditions but may also increase the likelihood of dying in a car crash, according to a new study.

The results show moderately obese individuals — those with a body mass index, or BMI, between 35 and 39 — have a 21-percent increased risk of death during a severe car crash compared with normal-weight individuals. Morbidly obese individuals — those with a BMI of 40 and above — have a 56-percent increased risk of death from car crashes. BMI is a ratio of weight to height and is considered an indicator of body fatness.

However, having just a few extra pounds actually conferred some protection against car-crash fatalities. Overweight individuals — those with a BMI between 25 and 29 — had a decreased risk of death compared with normal-weight individuals.

The results suggest having a little bit of a belly provides a cushioning effect during a crash. But a larger stomach puts an individual too close to the steering wheel, and therefore can boost the risk of mortality, said Dr. Dietrich Jehle, a professor of emergency medicine at the University at Buffalo School of Medicine in Buffalo, N.Y.

Interestingly, underweight individuals — those with BMIs below 18.5, also had an increased risk of death. This may be because these individuals lack any extra weight to cushion their crash, and they may also suffer from other illnesses, Jehle said.

"It's better to bring to your own air bag [aka "your belly"] as long as its small — if you have a little bit of padding you're protected as a driver in a motor vehicle crash," Jehle told MyHealthNewsDaily. "If you're really large then you are right on top of the steering column," and your body has less time to slow down before hitting the column, he said.

Obese individuals are also more likely to have serious illnesses, including cardiovascular disease and diabetes, and are more likely to have complications during surgery, which may contribute to their higher risk of death after a crash, the researchers say.

Car manufacturers should consider redesigning their vehicles to protect the one-third of obese Americans from injury during car crashes, Jehle said. For instance, it may help for larger individuals to be able to push their seats back farther than current vehicles allow. And smaller vehicles may be unsafe for those who are moderately to morbidly obese, Jehle said.

In addition, manufacturers should use obese crash-test dummies, in addition to the normal-weight ones, when testing cars for safety, the researchers urge. Currently, the only crash-test dummies available are modeled after norma-weight individuals. Obese crash-test dummies would give car designers a better idea of how larger bodies react during a crash, which in turn could lead to improvements in the car structure and possibly a reduction in car-crash mortality, the researcher say.

"It may make more sense to test vehicles with dummies that are more in line with what the population looks like," Jehle said.

Car crashes are the most common cause of injury-related death for those ages 3 to 33. In 2007, there were more than 41,000 deaths resulting from car accidents, according to the researchers.

The study is the largest to examine the impact of body size on car-crash fatalities.

Jehle and his colleagues analyzed information on deaths related to car crashes from the Fatality Analysis Reporting System, a national database.

The crashes, which had to result in at least one death to be listed, occurred between 2000 and 2005 and involved one or two vehicles. A total of 155,584 drivers were included in the study.

The results will be published in an upcoming issue of the American Journal of Emergency Medicine.

Pass it on: Very obese individuals have an increased risk of death during a car crash, but a little extra weight may actually have a protective effect.

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