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Department of Primary Care and Population Sciences
Royal Free and University College Medical School
Rowland Hill Street
London NW3 2PF
United Kingdom
E-mail: goya{at}pcps.ucl.ac.uk
Department of Public Health Sciences
St George's Medical School Hospital
London SW17 ORE
United Kingdom
Dear Sir:
Esmaillzadeh et al (1) recently published a study in Iranian men, which were much younger than those in our study, that claims that the waist-to-hip ratio (WHR) is a better marker of metabolic abnormalities than are body mass index (BMI) or waist circumference (WC). In their letter, they make a number of criticisms on the methods used in our article. Here, we respond to their main concerns.
Prevalence of metabolic syndrome
If our aim had been to estimate the prevalence of the metabolic syndrome in the population, then our definition of WC would not yield the correct prevalence. However, this article was not about prevalence per se. A major purpose of our article was to investigate the association between the different adiposity measures and metabolic abnormalities and to compare the predictive abilities of the different adiposity measures in the detection of metabolic abnormalities. Therefore, it would have been inappropriate to include WC as part of the metabolic syndrome definition. This would inevitably have led to a correlation between metabolic abnormalities and WC that would have been greater than those between metabolic abnormalities and the other indexes that we investigated. We stated this clearly in the Methods section but retained the term "metabolic syndrome," which is comparable with the definition used in a recent study that compared the association between WC and BMI and the metabolic syndrome (2).
Hypertension and lipid-lowering drugs
The results were not dependent on the definition of hypertension used; repeating the analyses with different definitions of hypertension did not affect the results. In our article, we stated that the definition of hypertension included men taking antihypertensive drugs. Although we did not specifically exclude men taking lipid-lowering drugs, men with a history of ischemic heart disease and diabetes (which accounted for most of the study subjects who were taking lipid-lowering drugs) were excluded. Our findings are thus highly unlikely to be confounded by men who were taking antihypertensive or lipid-lowering drugs.
Rate ratio
The rate ratio would not be appropriate for this analysis because the data were cross-sectional. Whereas the odds ratio derived from a logistic regression would be an overestimate of the risk ratio, the ranking of risk ratios obtained for the various anthropometric indexes would not be affected, so that the BMI and WC would still emerge as the best predictors.
Sensitivity and specificity
Sensitivity and specificity are useful measures of quantifying the predictive ability of anthropometric measurements, which were calculated and displayed in Figures 1 and 2 of our article in the receiver operating characteristic curves, which display sensitivity and specificity for a range of cutoffs. These analyses clearly showed that BMI and WC were the best predictors. The odd ratios usefully summarize these differences in predictive ability.
Cutoffs
The metabolic syndrome is used as a dichotomous variable, and the components are based on defined cutoffs. For clinical purposes, this is a more useful indicator of dyslipidemia or hypertension. We therefore analyzed our data as such. We do not believe that treating the metabolic abnormalities score as a quantitative variable would change the rankings of strengths of relations for the various adiposity indexes. Indeed, this would prevent our calculation of sensitivity and specificity (see above).
Waist-to-hip ratio
The major purpose of the article was to assess which measure (or measures) of adiposity would be most useful to identify men with metabolic abnormalities in clinical practice. We compared the waist-to-hip ratio with BMI and WC, and our data strongly suggested that WHR was neither as sensitive nor as specific as WC or BMI in these elderly men.
ACKNOWLEDGMENTS
The authors had no conflicts of interest.
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