Waist-to-Hip Ratio Strongest Predictor of Mortality Regardless of BMI

A recent cohort study published in JAMA Network Open by Irfan Khan and colleagues, utilizing data from the UK Biobank (UKB), has shed light on the relationship between different measures of adiposity and mortality risk. The study, conducted on British participants of British White ancestry, aimed to determine which among Body Mass Index (BMI), Fat Mass Index (FMI), and Waist-to-Hip Ratio (WHR) had the strongest and most consistent association with mortality.

In the study, a substantial cohort of participants was analyzed, comprising 387,672 individuals for the observational part of the study and 50,594 participants for the Mendelian randomization (MR) analysis. The average (mean [SD]) age of participants in the observational analysis was 56.9 (8.0) years, with 45.9% being male and 54.2% female. In the MR analysis, the average age was slightly higher, with a mean (SD) age of 61.6 (6.2) years, including 59.3% males and 40.6% females.

The study investigated the associations between various measures of adiposity and all-cause mortality. It found that the associations differed based on the measure used:

• BMI and FMI: The associations between measured BMI and FMI with all-cause mortality were characterised by a J-shaped curve. This implies that both low and high BMI or FMI values were associated with increased mortality risk.

• WHR: In contrast, the association of Waist-to-Hip Ratio (WHR) with all-cause mortality was linear when assessed using the hazard ratio (HR) scale. An increase of one standard deviation in WHR was linked to a HR of 1.41 (with a 95% confidence interval ranging from 1.38 to 1.43), demonstrating a consistent and direct relationship with mortality risk.

Moreover, the study employed genetically determined factors to assess these associations:

• Genetically determined WHR: This measure exhibited a notably stronger association with all-cause mortality than genetically determined BMI. An increase of one standard deviation in genetically determined WHR was associated with an odds ratio (OR) of 1.51, with a 95% confidence interval ranging from 1.32 to 1.72.

• Gender Differences: The study identified gender-based variations in the associations. In male participants, the association of genetically determined WHR with all-cause mortality was particularly robust, with an odds ratio of 1.89 (95% CI, 1.54-2.32). This difference was statistically significant, indicating that the WHR-mortality association was stronger in males compared to females.

Consistency Across BMI: Unlike BMI or FMI, genetically determined WHR's association with all-cause mortality remained consistent across different observed BMI categories. This suggests that WHR may be a more reliable predictor of mortality, irrespective of an individual's BMI. In summary, the study underscores the importance of considering waist-to-hip ratio as a valuable metric for assessing mortality risk, regardless of an individual's BMI. These findings could potentially reshape clinical practices, encouraging healthcare providers to prioritize evaluating adiposity distribution when assessing patients' health and mortality risk.

Reference:

Khan, I., Chong, M., Le, A., Mohammadi-Shemirani, P., Morton, R., Brinza, C., Kiflen, M., Narula, S., Akhabir, L., Mao, S., Morrison, K., Pigeyre, M., & Paré, G. (2023). Surrogate adiposity markers and mortality. JAMA Network Open, 6(9), e2334836. https://doi.org/10.1001/jamanetworkopen.2023.34836