Does BMI tell the whole story about patient weight?

August 7, 2019

A recent study examined associations between normal-weight central obesity and mortality among postmenopausal women.

Although most of the public health focus on obesity is centered on promoting a normal body mass index (BMI), central obesity (high-waist circumference [WC]) is not given the same attention and data on its association with long-term health are sparse. A recent study in JAMA Network Open examined associations between normal-weight central obesity and all-cause and cause-specific mortality among postmenopausal women in the United States. 

The nationwide prospective cohort study included data from 156,624 postmenopausal women enrolled in the Women’s Health Initiative between 1993 and 1998. The participants were observed through February 2017. The main outcome was mortality from all causes, including cardiovascular disease (CVD) and cancer.

The authors examined different combinations of BMI and WC. A BMI between 18.5-24.9 was considered normal weight, 25.0-29.9 was considered overweight, and BMI ≥ 30 was considered obese. WC ≤ 88 cm was considered normal and > 88 was considered high. Demographic factors, diet quality, and recreational activity were self-reported

Of the 156,624 women (mean [SD] age, 63.2 [7.2] yeasr), 43,838 deaths occurred across more than 2.8 million person years. Among these deaths, 12,956 were from CVD (29.6%) and 11,828 resulted from cancer (27.0%). Across BMI categories, women with central obesity were more likely than women without central obesity to be older and nonwhite, with less education, lower income, and lower neighborhood socioeconomic status (NSES) than women without central obesity. 

After adjusting for demographic characteristics, NSES, lifestyle factors, and hormone use, women with central obesity in each BMI category were at increased risk of all-cause mortality compared with women with normal weight and no central obesity. Women who were overweight or obese but had no central obesity were at a slightly lower risk of all-cause mortality. 

For all-cause mortality, the HRs were 1.31 (95% CI, 1.20 – 1.42, < .001) among women with normal weight and central obesity, 1.16 (95% CI 1.13-1.20, < .001) among women with overweight and central obesity, and 1.30 (95% CI, 1.27 – 1.34, P< .001) among women with obesity and central obesity. Women with normal weight and central obesity had a risk similar to women with obesity and central obesity and the risk was 13% to 44% higher than among women with any other BMI/WC combination. 

Associations of different BMI/WC combinations with all-cause, CVD and cancer mortality were generally similar across categories of age, race/ethnicity, education, income, NSES, diet quality, smoking status, physical activity, and estrogen use although the magnitudes of risk were greater for all-cause mortality among younger women (aged < 65).

 

The authors believe the most important takeaway from this study is that women with normal BMI but high central obesity are at an elevated risk for all-cause mortality, similar to the risk in obese women with high central obesity. This means that individuals with normal weight based solely on BMI could be missing out on opportunities for risk evaluation and intervention. Ob/gyns may want to consider including WC in their evaluations of patient weight to ensure that at-risk patients are not being neglected.