Using Body Shape To Predict Mortality Risk

A recent study published in JAMA examining central obesity indicated that body shape is a stronger mortality predictor than BMI.  

One noted limitation of body mass index to define obesity is the inability to include body shape in the formula. Previous research has indicated that central obesity (a.k.a. abdominal obesity) is associated with worse health outcomes, but there is limited evidence about patients with a normal body mass index that have central/abdominal obesity. A recent study by JAMA evaluated whether central/abdominal obesity was related to negative health outcomes in those with a normal body mass index.

This Women’s Health Initiative Study (WHI) was a randomized clinical trial n=68,132 and observational study n=93,676 of postmenopausal women aged 50-79 years. After exclusions, 156,624 women were included in the study. Height, weight, and waist circumference were measured at baseline and BMI values were as follows: normal weight = 18.5-24.9, overweight = 25.0 to 29.9, and obesity = 30.0 or greater. Obesity patterns were separated into six groups based on BMI and presence or lack of central/abdominal obesity. The primary endpoint of this study was all-cause mortality followed by cardiovascular disease mortality and cancer mortality. 

Results indicate that even after adjusting for demographics, lifestyle, hormone use, and education, women with central/abdominal obesity were at an increased risk of all-cause mortality independent of body mass index. In addition, women with a normal body mass index and central/abdominal obesity had a higher risk of cardiovascular disease and cancer mortality. Overall, women who were overweight and had central/abdominal obesity were at the greatest risk of poor health outcomes, while women who had a normal body mass index and central obesity had the second-highest risk of cardiovascular disease mortality. Numerous studies have linked central obesity to increased mortality risk, but few have evaluated this risk in patients with a normal body mass index and central obesity. To date, this study is the largest and longest study to evaluate normal-weight central obesity and clinical outcomes. 

These results may be explained by the negative effects of visceral fat and reduced muscle mass associated with central obesity. Visceral fat is linked to insulin resistance, high cholesterol, inflammation, and an increased risk for cardiovascular disease and cancer. Current guidelines do not represent a population with a normal weight and central obesity, and this may lead to the false security of health status. The strengths of this study include very large sample size, a prospective study design, and the length of the study. Limitations include a lack of generalizability of the study, that some participants did not have adipose imaging data, the body mass index cutoffs may not be appropriate in all populations, and only baseline exposure data was used. This study emphasizes the flaws of determining mortality risk based on body mass index alone. When calculating health outcomes waist circumference should be added to body mass index to better stratify risk. Current recommendations that exclude the measurement of abdominal fat in patients with a normal body mass index should be reconsidered. Additional research is needed to confirm these results in a more diverse population.

Practice Pearls:

• A normal BMI with central obesity is considered a high-risk profile for mortality.
•  Future guidelines should include the management of central obesity in all patients, not just those with overweight or obesity.
• Additional research is needed due to the lack of generalizability of this study, but the results are clinically relevant.

Sun, Yangbo, et al. “Association of Normal-Weight Central Obesity With All-Cause and Cause-Specific Mortality Among Postmenopausal Women.” JAMA Network Open, vol. 2, no. 7, 2019, doi:10.1001/jamanetworkopen.2019.7337.

Golzarri-Arroyo, Lilian, et al. “What’s New in Understanding the Risk Associated With Body Size and Shape?” JAMA Network Open, vol. 2, no. 7, 2019, doi:10.1001/jamanetworkopen.2019.7336.

 Kassey James, Pharm.D.Candidate, LECOM School of Pharmacy