"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," the researchers from the Safe Transportation Education and Research Center at the University of California wrote in the study.
The study is based on data from the US Fatality Analysis Reporting System between 1996 and 2008, which includes all fatalities that occur within 30 days of a crash.
During the study period, there were 57,491 crashes. Researchers then looked specifically for crashes that involved people who were driving cars that were similar both in size and type, and found 3,403 people who fit the criteria and who had available data on factors such as weight and seat-belt use. Of these people, nearly half were normal weight, about a third were overweight, and 18 percent were obese. (Obesity is defined as having a body mass index of 30 or higher, while overweight is defined as having a BMI between 25 and 29.9 and normal weight is defined as having a BMI between 18.5 and 24.9).
Researchers found an association between being obese and having an increased risk of dying in the car crash, with the risk going up the more obese the person was.
For example, among people whose body mass indexes (BMI) were between 30 and 34.9, the risk of dying in a car accident was 21 percent higher than people of normal weight. People with a BMI between 35 and 39.9 had a 51 percent higher risk of dying in a car accident, and people with a BMI of 40 or above had an 80 percent higher risk of dying in a car accident.
Researchers also found in the new study that nearly one-third of the people who died in the crashes also didn't wear their seat belts properly.
The researchers noted that it's possible that people who are obese may have other conditions that could make them less likely to survive a car accident. But still, they noted, other research has suggested reasons why a car crash might be deadlier for people with added weight. From the statement:
The authors point to other research, showing that the lower body of obese drivers is propelled further forward on impact before the seatbelt engages the pelvis, because of the additional soft tissue which prevents the belt from fitting snugly, while the upper body is held back.
This is hardly the first time research has suggested a higher risk of dying in a car crash for obese people. In 2010, a study conducted by University of Buffalo researchers showed that people who are morbidly obese have a 56 percent higher risk of dying in a car accident.
And last year, a study was presented at the annual meeting of the Society for Academic Emergency Medicine showing that people who are obese are less likely to buckle up than their normal-weight peers.
"It's clear that not wearing a seatbelt is associated with a higher chance of death," study researcher Dr. Dietrich Jehle, M.D., a professor of emergency medicine at the University of Buffalo School of Medicine and Biomedical Sciences, said in a statement. "We hypothesized that obese drivers were less likely to wear seatbelts than their normal weight counterparts. Obese drivers may find it more difficult to buckle up a standard seatbelt."