Waist-to-hip Ratio Predicts Early Death Better Than BMI

Introduction

Waist-to-hip ratio (WHR) is a stronger predictor of early death than Body Mass Index (BMI) and should be considered a superior measure of healthy weight, new research being presented at the annual meeting of the European Association for the Study of Diabetes (EASD) in Stockholm, Sweden (19-23 Sept 2022), has found.

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Body mass index is widely used to assess whether a person is at a healthy weight, with a BMI of 18.5-24.9 kg/m2 in the healthy range.

"However, BMI doesn't take into account fat distribution," says Irfan Khan, a medical student at the College of Medicine and Health, University College Cork, Cork, Ireland, who carried out the research with colleagues in Canada.

"It doesn't consider where fat is stored - whether it's accumulated around the hips or the waist. As a result, BMI doesn't reliably predict the risk of disease or mortality."

"We wanted to find out whether waist-to-hip ratio (WHR) or fat mass index (FMI) would more reliably predict mortality across different fat distributions."(1)

The researchers first investigated whether higher fat levels (adiposity) cause increased mortality or merely correlate with it.

The data analysis on UK Biobank participants with genes known to raise the risk of weight gain/obesity (i.e., genetically-determined adiposity) indicated that higher levels of fat cause increased mortality rather than merely correlated with it.

The researchers then applied genetically determined adiposity measures - information on the genes associated with BMI, WHR, and FMI - to data on 25,297 Caucasian men and women whose health had been tracked as part of the UK Biobank study until their death and 25,297 age, sex, and genetic ancestry-matched controls from the same study. (Average age of participants, 61.6 years, 59.3% male.)

This showed the relationship between WHR and death from any cause to increase linearly, meaning the risk of early death was lowest for those with the lowest WHR and then steadily increased with increasing WHR.

In contrast, BMI and FMI had a J-shaped relationship with all-cause mortality, meaning that those with either an extremely high or low BMI or FMI had an increased risk of mortality compared to those with a moderate BMI or FMI.

WHR was more strongly associated with all-cause mortality than BMI or FMI. For example, each one-unit increase in WHR increased the odds of early death by almost twice as much as a one-unit increase in BMI or FMI.

The association between WHR and all-cause mortality was stronger in males than females.

Unlike BMI and FMI, the relationship between WHR and all-cause mortality was consistent across different fat distributions.

Mr. Khan says:

"BMI's major limitation is that it doesn't take into account differences in fat distribution. This could mean that someone who has accumulated fat around their waist will have the same BMI as someone of the same age and height who stores their fat around the hips, despite the health risks of abdominal fat."

"WHR, however, better reflects levels of abdominal fat, including visceral fat, which wraps around the organs deep inside the body and raises the risk of a range of conditions, including type 2 diabetes and heart disease."

"With WHR the message is simply: the lower the WHR, the lower your mortality risk."

He adds that although the results need to be replicated in individuals of diverse genetic ancestry, they suggest that having a lower WHR is better, irrespective of the population studied.

"This is a further advantage over BMI, where optimal BMI varies from one population to the other," explains Mr. Khan.

The study's authors say that although they used genetically determined WHR in their analysis, their findings apply equally to the conventional definition of WHR. This quick and easy measurement involves dividing waist circumference by hip circumference.

They conclude that the waist-to-hip ratio should replace BMI as a simple measure of a healthy weight.

Mr. Khan says:

"Clinical recommendations and interventions should prioritize setting healthy WHR targets rather than general BMI targets."

"A more accurate measure of a healthy body shape may make a significant difference to the ill health and deaths caused by type 2 diabetes, heart disease, some cancers, and numerous other conditions."

Waist-to-hip Ratio Stronger, More Consistent Predictor of All-cause Mortality than BMI

Background and Aims:

Current clinical guidelines recommend a body mass index (BMI) between 18.5-24.9 kg/m2 . However, BMI does not consider inter-individual variation in body composition and is thus not consistent in predicting disease or mortality risk. We sought to determine whether current BMI recommendations are valid when accounting for body composition and which BMI, waist-to-hip ratio (WHR), and fat mass index (FMI) is the strongest and most consistent predictor of all-cause mortality across the range of body composition.

Materials and Methods:

We partitioned the British Caucasian UK Biobank (UKB) population (N= 387,672) into two subsets: a discovery cohort (N = 337,078) and validation cohort (N = 50,594). The discovery cohort was used to derive genetically-determined adiposity measures, while the validation cohort was used for all subsequent analyses. Observational relationships between BMI, WHR, and FMI with mortality from all-cause, cancer, cardiovascular disease (CVD), respiratory disease, or non-CVD - were analyzed. Mendelian randomization (MR) was then used to assess the causality of observed associations and to investigate effects across percentiles of BMI, WHR, and FMI.

Results:

The study population consisted of 25,297 deaths and 25,297 randomly selected age- and sex-matched controls from the UKB (mean (SD) age: 61.6 (6.2), 59.3% male). Observational relationships between BMI and FMI with all-cause mortality were J-shaped, whereas the relationship between WHR with all-cause mortality increased linearly. Genetically-determined WHR had a stronger association with all-cause mortality compared to BMI or FMI and exhibited a stronger effect in males compared to females (OR per SD of genetically-predicted WHR (95% CI): 1.51 (1.32 - 1.72); genetically-predicted BMI (95% CI): 1.29 (1.20 - 1.38); genetically-predicted FMI (95% CI): 1.26 (1.20 - 1.32), P for all analyses and comparisons < 0.05). Unlike BMI or FMI, the relationship between genetically- determined WHR and all-cause mortality was consistent across all percentiles of BMI, FMI, or WHR (P > 0.05).

Conclusion:

In contrast to BMI, WHR has the strongest causal effect on the risk of mortality regardless of the levels of adiposity and body composition but shows evidence of differential effects according to sex. Clinical recommendations and interventions should prioritize setting healthy WHR targets for males and females rather than general BMI targets. More precise recommendations for body shape may significantly affect disease burden and deaths due to excess adiposity.

(1). BMI is defined as weight in kilograms divided by height in meters squared. FMI is the weight of body fat in kilograms divided by height in meters squared. The waist-to-hip ratio is waist circumference divided by the circumference of hips.

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Attribution/Source(s):

This peer reviewed publication was selected for publishing by the editors of Disabled World due to its significant relevance to the disability community. Originally authored by European Association for the Study of Diabetes (EASD), and published on 2022/09/23 (Edit Update: 2024/03/07), the content may have been edited for style, clarity, or brevity. For further details or clarifications, European Association for the Study of Diabetes (EASD) can be contacted at bristol.ac.uk. NOTE: Disabled World does not provide any warranties or endorsements related to this article.

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