By Sankar Navaneethan, MD, MPH
CLEVELAND, Ohio—Over one-third of the U.S. population is obese and over 10 percent have chronic kidney disease (CKD) posing enormous burden on the health care system.
Previous studies have shown obesity as an independent risk factor for the development and progression of kidney disease. Various anthropometric measures are being used to define obesity, including body mass index (BMI). BMI is an anthropometric measure of whole body adiposity that does not differentiate fat mass and muscle mass. In fact, high BMI has been associated to better survival in kidney disease population. Recent studies have shown that waist circumference (WC), a measure of visceral or abdominal adiposity, is a better predictor of cardiovascular disease and mortality in CKD population.
Whether obesity is associated with CKD complications and whether BMI and WC have differential associations with CKD complications have not been explored in previous studies. Sankar Navaneethan, MD, a nephrologist in the Glickman Urological and Kidney Institute at Cleveland Clinic and lead author of a study on obesity and CKD complications, examined the associations of WC and BMI with CKD complications (anemia, secondary hyperparathyroidism, hyperphosphatemia, metabolic acidosis, hypoalbuminemia, and hypertension) using data from the National Health and Nutrition Examination Survey 1999-2006 (NHANES) after adjusting for relevant confounding variables. The findings were published in the September 2012 issue of the American Journal of Nephrology.
The analysis included 2,853 adult participants with CKD. BMI was calculated as weight in kilograms divided by the measured height in meters squared and participants were classified as obese if they had a BMI >30 kg/m2. WC was categorized as high risk for men with a measured WC >102 cm and women with a measured WC >88 cm.
In the logistic regression analysis, the researchers found that an increase in BMI by 2 kg/m2 and WC by 5 cm were associated with an increased odds of having secondary hyperparathyroidism, hypoalbuminemia, and hypertension in those with CKD. CKD par ticipants with BMI >30 kg/m2 have higher odds of hypoalbuminemia and hypertension than those with BMI <30 kg/m2. CKD participants with high WC have higher odds of hypoalbuminemia and hypertension, and lower odds of having anemia than those with low WC. CKD participants with BMI >30 kg/m2 and high WC (who would meet both the criteria of obesity) have higher odds of secondary hyperparathyroidism, hypoalbuminemia and hypertension than participants with BMI <30 kg/m2 and low WC. CKD participants with BMI <30 kg/m2 and high WC (vs. <30 kg/m2 and low WC) were not associated with any of the CKD complications.
BMI data is readily available in clinical settings and whether WC details provide additional prognostic information relating to CKD complications is unclear. This analysis of a nationally representative cohort showed that both BMI and WC are associated with CKD complications such as secondary hyperparathyroidism, hypertension and hypoalbuminemia among those with CKD.
Among those with BMI <30 kg/m2, higher WC was not associated with any CKD complications. The observed associations between obesity and secondary hyperparathyroidism might be related to the lower vitamin D levels among those who are obese.
Hypoalbuminemia associated with obesity in CKD might reflect the higher inflammatory burden seen amongst them.
Further, those who are obese have heightened sympathetic system activity contributing to the hypertension noted in those who are obese. Cumulatively, the study results suggest the need for closely monitoring the development of CKD complications among those CKD patients who are obese.