Elsayed EF et al. (2008) Waist-to-hip ratio, body mass index, and subsequent kidney disease and death. Am J Kidney Dis 52: 49–57

Most studies of associations between obesity and subsequent chronic kidney disease (CKD) used BMI to measure obesity. However, BMI might not reflect obesity levels in individuals with atypical body composition, especially in those with increased muscle mass. Waist:hip ratio specifically measures central obesity (visceral adiposity) and identifies individuals at increased risk of metabolic dysfunction.

Elsayed and colleagues analyzed pooled data from 13,324 participants in the Atherosclerosis Risk in Communities Study and the Cardiovascular Health Study. At baseline, participants' mean age was 57.4 years, mean BMI was 27.2 kg/m2, and mean waist:hip ratios were 0.96 in men and 0.89 in women. During follow-up (9.3 years), CKD developed in 300 or 710 patients (2.3% or 5.5%), when defined on the basis of serum creatinine level or estimated glomerular filtration rate, respectively.

After adjustment for confounding variables including age, sex, race, education level, comorbid conditions, and baseline renal function, BMI no longer correlated with development of CKD. By contrast, increased waist:hip ratio still correlated strongly with incident CKD, which suggests that waist:hip ratio identifies additional risk for CKD beyond that conferred by pre-existing diabetes, hypertension, or dyslipidemia. In addition, increased waist:hip ratio was associated with increased risk of a composite outcome (decreased kidney function and death), whereas increased BMI seemed to protect against this outcome. Interestingly, increased BMI also favors survival in studies of patients on dialysis or with heart failure.

The authors recommend that future studies should use waist:hip ratio instead of BMI to assess obesity.