Daily Dose: Waist-to-Hip Ratio Better Predictor for Mortality than BMI?

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Patient Care brings primary care clinicians a lot of medical news every day—it’s easy to miss an important study. The Daily Dose provides a concise summary of one of the website's leading stories you may not have seen.

Last week, we reported on findings from a study published in JAMA Network Open Diabetes and Endocrinology that analyzed which of body mass index (BMI), fat mass index (FMI), and waist-to-hip ratio (WHR) has the strongest and most consistent association with mortality.

The study

To create the study cohort, researchers tapped the UK Biobank data set issued on August 3, 2021, comprised of 408 160 individuals who had appropriate genotypic data for analysis. After exclusions, the final cohort numbered 387 672; this group was divided to create a discovery cohort (n = 337 078) and a validation cohort (n = 50 594) to facilitate derivation polygenic risk scores used to assess predisposition to the 3 measures. Outcomes of primary interest to the researchers were all-cause, cancer-related, cardiovascular disease (CVD)–related, and respiratory disease–related mortality, along with mortality resulting from all other diseases (other).

The exposure-outcome associations were analyzed using Cox proportional hazard models and Mendelian randomization (MR). Nonlinear MR was also conducted to assess the consistency of adiposity-mortality associations across different body composition levels.

Findings

Investigators reported a J-shaped association for both BMI and FMI with all-cause mortality. The association between WHR and death from any cause, however, was linear. The study found, in a departure from previous research, that genetically determined WHR had a stronger association with all-cause mortality and was more robust in men. In contrast to BMI or FMI, the genetically determined WHR–all-cause mortality association was consistent across quantiles of observed BMI.

The team's observational analyses yielded positive associations for all 3 adiposity measures with death related to cancer and CVD mortality; for both FMI and BMI, they found a J-shaped association with death from respiratory disease and "other" specific causes.

Authors' comment

"Our study found that the association between WHR and all-cause mortality was potentially causal, stronger than BMI, and consistent across quantiles of BMI. WHR is easier to measure than FMI due to FMI requiring BIA, which can be expensive and inaccessible. Our MR findings support a possible causal relationship between WHR and mortality. This suggests that not only can WHR be used as clinical risk marker, but it may be a suitable intervention target, given weight loss is associated with a lower WHR."

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