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Waist-To-Hip Circumference Ratio (WHR) May Be a Better Predictor Than BMI

Submitted by Intelligentactile on July 6, 2012

Waist-to-hip circumference ratio (WHR) may be a better predictor of all-cause mortality in older adults vs body mass index (BMI), according to the results of a study reported in the October issue of the Annals of Epidemiology.

“Basically, it isn’t BMI that matters in older adults — it’s waist size,” lead author Preethi Srikanthan, MD, from the University of Southern California, Los Angeles, said in a news release. “Other studies have suggested that both waist size and BMI matter in young and middle-aged adults and that BMI may not be useful in older adults; this is one of the first studies to show that relative waist size does matter in older adults, even if BMI does not matter.”

The goal of this study was to evaluate the association between 3 measures of obesity and all-cause mortality in a group of healthy older adults, using data from the MacArthur Successful Aging Study, a longitudinal study of high-functioning men and women aged 70 to 79 years at baseline. The association of BMI, waist circumference, and WHR with all-cause mortality risk was determined with use of proportional hazards regression to adjust for sex, race, age at baseline, and smoking status. The investigators tested for obesity interactions with sex, race, and smoking status and performed stratified analyses based on the results of interaction testing.

In both unadjusted and adjusted analyses, there was no association between all-cause mortality and BMI or waist circumference, whereas all-cause mortality increased with WHR. There was an interaction with sex, with a graded relationship between WHR and mortality in women (relative hazard, 1.28 per 0.1 increase in WHR; 95% confidence interval [CI], 1.05 – 1.55). In men, a threshold relationship was observed (relative hazard, 1.75 for WHR > 1.0 vs WHR ≤1.0; 95% CI, 1.06 – 2.91).

“WHR, rather than BMI or WC [waist circumference], appears to be the more appropriate yardstick for obesity-related risk stratification of high-functioning older adults, and possibly all older adults,” the study authors write.

Limitations of this study include possible underestimate of BMI because height and weight were self-reported. In addition, WHR, waist circumference, and BMI were based on single measurements.

“Given our use of self-reported weight and height data, these findings need to be confirmed in other cohorts of older adults,” the study authors conclude. “Further research into the mechanisms underlying the increased health risks associated with high WHR is also needed, specifically to delineate the role of intra-abdominal visceral fat, relative to pelvic bone size, gluteal muscle, and gluteal fat, in older adults’ health risks.”

This study was partly supported by the National Institute on Aging. The study authors have disclosed no relevant financial relationships.

Ann Epidemiol. 2009;19:724-731. Abstract

Clinical Context

Obesity is linked to a shortened life span because of associated risks for insulin resistance, diabetes, myocardial infarction, stroke, and other morbidities. Even after age 60 years, the incidence of obesity continues to increase with age.

In older adults, the relationship between obesity and mortality is still unclear. BMI may not be an optimal measure of obesity in this age group. If abdominal adipose tissue is the predominant underlying factor in the health risks associated with obesity, measures of absolute and relative waist size, such as waist circumference and WHR, may be more clinically meaningful.

Study Highlights

Data for this analysis came from the MacArthur Successful Aging Study, a longitudinal study of high-functioning men and women aged 70 to 79 years at baseline. The goal of this analysis was to determine the association between BMI, waist circumference, and WHR and all-cause mortality in healthy, high-functioning older adults. The average age of the participants was 74 years. Proportional hazards regression was used to adjust for sex, race, age at baseline, and smoking status. Stratified analyses were based on the results of testing for obesity interactions with sex, race, and smoking status. All-cause mortality was not associated with BMI or waist circumference in either unadjusted or adjusted analyses. To decrease the potential for residual confounding by recent weight loss caused by a terminal condition, deaths in the first 2.5 years of follow-up (and first 7 years in a second sensitivity analysis) were excluded. These exclusions had only minimal effects on the nature of the relationship of WHR to mortality. All-cause mortality rate increased with WHR, and there was an interaction with sex. In women, there was a graded relationship between WHR and mortality, so that each 0.1 increase in WHR was associated with a 28% relative increase in mortality rate. In men, there was a threshold effect, with mortality rate 75% higher in men with a WHR of more than 1.0 (waist larger than hips) vs men with a WHR of 1.0 or less. The investigators concluded that WHR vs BMI or waist circumference was a better measure for obesity-related risk stratification of high-functioning older adults, and possibly all older adults. Limitations of the study include self-report of height and weight leading to possible underestimate of BMI, and only single measurements of WHR, waist circumference, and BMI.

Clinical Implications

In high-functioning older adults enrolled in the MacArthur Successful Aging Study, all-cause mortality was not associated with BMI or waist circumference in either unadjusted or adjusted analyses. In contrast, all-cause mortality rate increased with WHR. In women, there was a graded relationship between WHR and mortality, whereas in men, there was a threshold effect, with mortality rate 75% higher in men with a WHR of more than 1.0 vs men with a WHR of 1.0 or less.