The relationship between body weight and risk of death and serious injury in motor vehicle crashes

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Abstract

We sought to investigate the effect of increased body weight on the risk of death and serious injury to occupants in motor vehicle crashes. We employed a retrospective cohort study design utilizing data from the National Automotive Sampling System, Crashworthiness Data System (CDS), 1993–1996. Subjects in the study included occupants involved in tow-away crashes of passenger cars, light trucks, vans and sport utility vehicles. Two outcomes were analyzed: death within 30 days of the crash and injury severity score (ISS). Two exposures were considered: occupant body weight and body mass index (BMI; kg/m2). Occupant weight was available on 27 263 subjects (76%) in the CDS database. Mortality was 0.67%. Increased body weight was associated with increased risk of mortality and increased risk of severe injury. The odds ratio for death was 1.013 (95% CI: 1.007, 1.018) for each kilogram increase in body weight. The odds ratio for sustaining an injury with ISS⩾9 was 1.008 (95% CI: 1.004, 1.011) for each kilogram increase in body weight. After adjustment for potentially confounding variables (age, gender, seatbelt use, seat position and vehicle curbweight), the significant relationship between occupant weight and mortality persisted. After adjustment, the relationship between occupant weight and ISS was present, although less marked. Similar trends were found when BMI was analyzed as the exposure. In conclusion, increased occupant body weight is associated with increased mortality in automobile crashes. This is probably due in part to increased co-morbid factors in the more overweight occupants. However, it is possibly also due to an increased severity of injury in these occupants. These findings may have implications for vehicle safety design, as well as for transport safety policy.

Introduction

Notable contributions to the advancement of automotive safety have been made in several fields including roadway engineering, driver behavior, and automobile design. Safety-related automobile design has been promoted by such advances as seatbelts, airbags, collapsible steering columns, and side impact protection. Many of these safety design features were refined based on tests conducted using anthropomorphic test devices. Traditionally, these represented average size (70 kg) males. The efficacy of these safety design features is likely to vary based on the weight and dimensions of the occupant's body. This possibility has led to the development of a variety of anthropomorphic test devices, representing both genders as well as a range of ages and body sizes (Mertz, 1993).

The influence of the weight and dimensions of the occupant's body on the likelihood of injury or death in real world crashes is incompletely understood however. Several reports have drawn attention to injuries in short stature women and children (Dischinger et al., 1995, Braver et al., 1998, Cooper et al., 1998, Giguere et al., 1998, Graham et al., 1998, McCaffrey et al., 1999). There is also evidence that increased body weight may increase the risk of severe injury and death in motor vehicle crashes and other blunt injury mechanisms. One case series showed an increased risk of injuries to the chest, pelvis, and extremities among more overweight occupants involved in crashes (Boulanger et al., 1992). Another inpatient study showed mortality to be higher among admitted injured patients with high body mass index (BMI) compared to those with normal BMI (Choban et al., 1991). Some studies have also shown an increased risk of more severe extremity injuries in falls among individuals with higher BMI (Bostman, 1994, Spaine and Bollen, 1996).

The purpose of the present study was to use national crash data to investigate the potential effect of increased body weight on the risk of death and serious injury to occupants in motor vehicle crashes.

Section snippets

Methods

The National Automotive Sampling System (NASS) of the National Highway Traffic Safety Administration carries out an ongoing sampling of crashes in the United States. One component of this system, the Crashworthiness Data System (CDS) is a national probability sample of light passenger vehicles (passenger cars, vans, utility vehicles, and pickup trucks) involved in police-reported, tow-away crashes. CDS contains data on automotive damage, occupant injuries, and injury sources.

At 24 sites

Crashes

There were data on 36 206 occupants 15 years and older in the CDS database for the study years, representing a national sample of 11 987 367 crashes. Occupant body weight was available for 27 263 (weighted: 76%) occupants. Weight and height were available for 26 727 (75%). All subsequent analysis was limited to these occupants.

Slightly more than half of the occupants (54%) were male and the mean age was 34.4 yr (Table 1). Proper seatbelt use was reported for 76% of occupants. Airbags were

Discussion

Increased body weight, and in particular increased body fat as measured by increased BMI has been associated with a range of health problems, including hypertension, diabetes, atherosclerosis, and gallbladder disease. These effects lead to an increase in the mortality rate and a decrease in longevity on the part of more overweight individuals (Bray, 1985, National Institutes of Health Consensus Development Panel on the Health Implications of Obesity, 1985, Van Itallie, 1985, Pi-Sunyer, 1991,

Acknowledgements

The research described in this report was financed by the General Motors Corporation pursuant to an agreement between GM and the US Department of Transportation. The study was carried out as part of the Crash Injury Research and Engineering Network (CIREN). This paper was presented in part at the Fifth World Conference on Injury Prevention and Control, March 5–8, 2000, New Delhi, India.

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