Other research has suggested that obese drivers experience much more forward motion during a car crash than non-obese drivers because their additional soft tissue keeps the seat belt from immediately tightening around their pelvis.
This new study provides troubling evidence that the result of that extra forward motion may be a greater risk of death.
An extensive database
For the study, University of California-Berkeley health economist Thomas M. Rice and University of West Virginia epidemiologist Motao Zhu analyzed 1996-2008 data from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System (FARS), which keeps a running census of fatal traffic accidents in the U.S. They found 41,296 collisions in that database in which both drivers were aged 16 or older and one or both of the drivers died.
The researchers then gathered data on the height and weight of the drivers (from their driver’s licenses) and divided them into four groups according to the World Health Organization’s body-mass-index categories (underweight, normal range, overweight and obese). Other information about the drivers was also collected, including gender, seat-belt use, airbag deployment and the type of collision (whether it was head-on or not).
A total of 6,806 drivers involved in 3,403 collisions were selected for the final analysis. Of these, the researchers found complete information on 5,225 drivers. Some 46 percent were of normal weight (a BMI of 18.5 to 24.9), 33 percent were overweight (25 to 29.9), 18 percent were obese (30 and above), and 3 percent were underweight (less than 18.5).
Risk rises with obesity level
After crunching the data, Rice and Zhu found that the death rate among those drivers who were underweight or overweight was about the same as for those of normal weight.
But among the obese drivers, the risk of death was significantly higher — and the risk rose as the obesity of the drivers increased. The risk was 21 percent higher for those with a BMI of 30 to 34.9, 51 percent higher for those with a BMI of 35 to 39.9 and 80 percent higher for those with a BMI of 40 or greater.
Gender and risk
The researchers looked at the other information collected about the drivers and the accidents to see if something like seat-belt use or type of collision could explain the differences in the fatality rates between the obese and non-obese drivers. None could.
Obese women were, however, at greater risk of dying in the collisions than obese men. In fact, those in the top category of obesity (BMI of greater than 40) were almost twice as likely to be killed as similarly obese men.
Gender had one other effect on risk: Underweight men were 78 percent more likely to die in a traffic accident than normal-weight men. That was not true for underweight women, however.
‘Important public health implications’
These findings suggest that automobile manufacturers need to start considering the body mass of drivers when designing automobile safety features. More than one-third of U.S. adults (35.7 percent) are obese, according to the Centers for Disease Control and Prevention. That number is expected to rise to 42 percent by 2030. In addition, the number of Americans who are severely obese (40+ BMI) is expected to more than double from today’s 4.9 percent to 11 percent in 2030.
“The ability of passenger vehicles to protect overweight or obese occupants may have increasingly important public health implications, given the continuing obesity epidemic in the USA,” Rice and Zhu concluded. “… It may be the case that passenger vehicles are well designed to protect normal weight vehicle occupants but are deficient in protecting overweight or obese occupants.”