Body Mass Index, CKD and ESRD: Is There a Link?

In an article published in March issue of the American Journal of Kidney Diseases, the association between race, body mass index (BMI), and progression to end-stage renal disease (ESRD) or death is explored. Corresponding author Dr. Revekka Babayev (RB) discusses their findings with Dr. Sean Kalloo (eAJKD), eAJKD Contributor.

eAJKD: What are the main points of your article?

RB: In this biracial study examining over 12,500 participants with chronic kidney disease (CKD) stages 3 and 4 who presented for KEEP screening activities and were followed for eight years, we report that race but not BMI level was a risk factor for progression to ESRD. African American race was associated with higher incidence of ESRD, but not mortality. BMI > 30kg/m2 was associated with decreased mortality in the subgroup with class I obesity (BMI 30-35 kg/m2), but did not affect kidney survival. There was no significant interaction between race and BMI for either ESRD or mortality outcomes in our study.

eAJKD: You conclude that there does not appear to be a significant interaction between race and BMI in progression to ESRD or death. What is the clinical relevance of this conclusion when assessing and managing CKD?

RB: We found that race but not BMI level was associated with worse kidney survival, with lack of interaction between the two. This suggests that African Americans, irrespective of BMI level, may possess a different risk profile than whites with CKD. Despite higher levels of obesity among African Americans, obesity did not contribute to risk of ESRD. This is in contrast to some recent literature that linked obesity to worse kidney outcomes. Although it is still unclear what risk factor drives the race discrepancy, our data supports the previously published papers linking higher prevalence of hypertension, albuminuria, and diabetes to worse kidney outcomes. This study provides useful information for relaying risk to patients, and highlights the need for further studies to assess the interaction between race and obesity with kidney and overall survival.

eAJKD: Please describe some of the limitations of your study.

RB: This study has several limitations. Given that baseline values are from a cross-sectional dataset (i.e., only one screening visit), we are forced to rely on one data point to evaluate exposures, and assume that the abnormalities in serum creatinine and urinary albumin excretion represent chronic disease states. We also do not have detailed information on participants’ medications, and therefore cannot adjust for use of drugs, such as renin-angiotensin system blockers, that potentially affect ESRD outcomes. Moreover, the effect of BMI on mortality appeared to be limited in our population to participants only with class 1 obesity, while some prior studies have documented an association that continued into the morbidly obese population. We may have seen more uniform, if not different, results if we used waist circumference data instead of BMI, as waist circumference may be a better measure of adiposity. In the REGARDs study, for example, while there appeared to be a trend toward decreased mortality with higher BMI, after adjustment for covariates including BMI, higher mortality rates were noted for all waist circumference categories compared with the referent. The KEEP screenings only recently included waist circumference measurements, and relying on this metric would have severely limited the available participants for this study.

eAJKD: What can a clinician take away from this study in terms of management of CKD patients?

RB: The main take away point from the paper is that we still have a lot to learn about the racial differences in CKD, and the complicated role of obesity in our CKD population. At present, we should focus our energies on modifiable risk factors known to be associated with worse kidney survival, such as management of hypertension, albuminuria, and diabetes. It is still a good strategy to target obesity in patients with CKD, and this strategy should be applied regardless of race or ethnicity.

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