Central obesity may increase mortality risk in those with normal BMI
Body mass index is limited as a sole measure of adiposity in clinical practice, in part because it makes no distinction between fat and lean mass, an editorial noted.
Patients with normal body mass index (BMI) but central obesity, or a higher amount of fat in their abdominal area, could be at higher risk for death, according to a new study.
Researchers performed a stratified, multistage probability study using data from the Third National Health and Nutrition Examination Study (NHANES III) to evaluate risk for total and cardiovascular mortality in patients with central obesity and a normal BMI. They used multivariable Cox proportional hazards models to look at patterns of obesity as defined by BMI and waist-to-hip ratio (WHR) and total and cardiovascular mortality risk. Study results were published online Nov. 10 by Annals of Internal Medicine.
A total of 15,184 adults in NHANES III were included in the study. Age range was 18 to 90 years (mean, 45 years), and slightly over half of participants (52.3%) were women. Median follow-up was 14.3 years. BMI was categorized as normal (18.5 to 24.9 kg/m2) in 6,062 participants (39.9%), overweight (25 to 29.9 kg/m2) in 5,249 participants (34.6%), and obese (≥30 kg/m2) in 3,873 participants (25.1%). When World Health Organization criteria for central obesity based on WHR were applied (WHR ≥0.85 in women and ≥0.90 in men), 10,655 participants (70.2%) met the definition. WHR was considered large (>1.0) in 322 men (11.0%) and 105 women (3.3%) whose BMI was normal, 1,064 men (37.0%) and 289 women (12.0%) whose BMI indicated overweight, and 928 men (63.0%) and 336 women (14.0%) whose BMI indicated obesity. A total of 3,222 deaths occurred during the study period, 1,404 (43.5%) attributable to cardiovascular disease.
In multivariable Cox proportional hazards analysis, the researchers found that WHR was associated with higher mortality risk but that BMI was not. Hazard ratios were then estimated for total and cardiovascular deaths related to normal-weight central obesity. Men with normal-weight central obesity were estimated to have higher total mortality risk than men with any other BMI-WHR combination: 87% higher than men with a similar BMI but no central obesity and more than 2-fold higher than men who were overweight or obese but had no central obesity. For women, total mortality risk was 48% higher in those with normal-weight central obesity than in those with a similar BMI but no central obesity; those with normal-weight central obesity had a mortality risk that was 40% and 32% higher, respectively, than women who were overweight or obese according to BMI but had no central obesity.
The authors noted that NHANES data on comorbidities were based on self-report, that the technique used to measure waist circumference was different from that recommended by the World Health Organization and others, that misclassification bias could not be excluded, and that body fat distribution was based only on anthropometric indicators. However, they concluded, their findings suggest that patients with normal-weight central obesity should be targeted for preventive strategies, such as lifestyle modification.
“Future studies should focus on identifying factors associated with the development of normal-weight central obesity and better understanding the effect of normal-weight central obesity on health outcomes,” they wrote. “Until such data are available, the use of BMI with measures of central obesity may provide better adiposity-related risk factor stratification in clinical practice than either method alone.”
The author of an accompanying editorial noted that BMI is limited as a sole measure of adiposity in clinical practice, in part because it makes no distinction between fat and lean mass. “To better target persons at greatest risk, such as those who already have excess or increasing levels of adiposity or those with disproportionate abdominal fat in relation to BMI, these new data provide evidence that clinicians should look beyond BMI,” the editorialist wrote. “Although assessing for total fat mass with BMI to identify patients at greater cardiovascular risk is a good start, it is not sufficient.”