If you live in the United States, you've noticed that a lot of people are overweight or obese. You're overweight if your body mass index is between 25 and 30, and obese if it is 30 or greater (not due to atypical amounts of muscle).
In fact, this description applies to roughly two-thirds of Americans. Even one-third of American children are overweight or obese.
This issue got brief attention in the United States this past February, when "news" reporters found it in their hearts to briefly interrupt their onslaught of war pornography and celebrity gossip, by giving airtime to the presidential announcement of programs intended to help eliminate childhood obesity within a generation. One can easily debate whether this "plan" will help or not.
It's inarguable that tens of billions of dollars are spent every year on the health-related complications brought about by obesity. It therefore makes sense for Americans to stop packing on the pounds.
Recent research reported by Shankuan Zhu (Medical College of Wisconsin, United States, and Zhejiang University, China) and coworkers gives even more reason to lose weight. Additionally, they provide guidance on how to deal with conditions as they are today.
They have unraveled some of the details underlying the observation that obese men are generally at greater risk of injury after a motor vehicle accident than other men or even obese women. This information should assist motor vehicle manufacturers in designing more appropriate safety restraints.
Original data.
Little research has investigated the relationship between obesity and the risk of injury after a motor vehicle accident, especially in relation to gender. However, since obese women tend to have more fat in the lower body and obese men in the upper body, it's reasonable to speculate that there will be differences in their injuries after an accident.
The scientists studied data from the Crashworthiness Data System, a part of the National Automotive Sampling System. They included thousands of passenger car or truck drivers, at least 18 years old, involved in frontal collision accidents sometime from 2001 to 2005.
They excluded people if all clearly relevant data was not available (e.g. the person's weight was unknown), or they were not representative of obese individuals (e.g. the person was pregnant). Many other possible confounding factors were studied in addition to obesity, such as vehicle type, seatbelt use, and weather conditions, to see if they statistically influenced the results.
The scientists also ran computer simulations of frontal collision accidents of motor vehicles. Herein, they could experimentally adjust the body mass index of a simulated person, and observe the resultant injuries after an accident.
Overweight and obese males are at enhanced risk of injury.
The scientists found in both the experimental data and computer simulations that, relative to obese women, obese men were more likely to be injured in the upper body regions of the spine, thorax, abdomen, face, and head. Again relative to obese women, obese men were more likely to be seriously injured in the upper body regions of the spine, thorax, and head.
What causes these differences in gender and injurity severity? The scientists speculate that since obese males tend to have more fat in the upper body, an abrupt change in velocity may distribute more force to these body regions in an accident.
Limitations of the study due to the experimental data are mostly related to information that was unavailable in the database, such as vision impairment. A limitation of the study due to the computer simulations was that detailed data on the stress and strain of tissue, joints, and bone was unavailable.
Major strengths of this study include the large number of individuals studied, restriction to frontal collision data, and the disentanglement of gender in relation to injury. Additionally, the computer simulations were in broad agreement with the experimental data, corroborating the scientists' link between obesity and the risk of injury in motor vehicle accidents.
Implications.
The data reported by Zhu and coworkers, demonstrating the increased risk of injury in motor vehicle accidents among overweight and obese Americans, especially among males, will be useful to safety engineers who want to reduce the risk of injury among typical American drivers. This study should also provide further incentive for overweight and obese Americans to reduce their weight, as much as realistically possible.
for more information:
Zhu, S., Kim, J.-E., Ma, X., Shih, A., Laud, P. W., Pintar, F., Shen, W., Heymsfield, S. B., & Allison, D. B. (2010). BMI and Risk of Serious Upper Body Injury Following Motor Vehicle Crashes: Concordance of Real-World and Computer-Simulated Observations PLoS Medicine, 7 (3) DOI: 10.1371/journal.pmed.1000250