Risk is greater for overweight individuals than for those of normal weight, meta-analysis shows.
The positive association between obesity and kidney disease (KD) is strongly supported by results of a recent meta-analysis by Wang et al (Kidney Int. 2008;73:19-33) that demonstrate a significantly increased risk for people with BMI greater than the normal range of 18.5-25 kg/m2.
Along with CKD, the study also examined the occurrence of renal calculi and kidney cancer. According to the authors, 24.2% and 33.9% of KD cases among American men and women, respectively, could be prevented if overweight and obesity were eliminated.
The meta-analysis looked at more than 40 epidemiologic studies published from 1980 to 2006, with a focus on 18 prospective cohorts for reliability of findings, ability to determine causality, and generalizability of results. Of significance, persons categorized as overweight (BMI greater than 25 but less than 30 kg/m2) had a 40% increased risk of kidney disease compared with normal-range BMI, whereas obesity (BMI over 30 kg/m2) was associated with an 83% higher risk.
Among individuals with a BMI greater than 30 kg/m2, women had a 92% greater risk of kidney disease compared with a 49% increased risk for men, possibly because of differences in body composition (percent fat vs. muscle). The researchers acknowledge that more studies are needed to determine etiologic factors.
Paradoxically, higher BMI seems to confer survival benefit to patients with stage 5 CKD on dialysis. This reverse epidemiology was evident in a study by Glanton et al (Ann Epidemiol. 2003;13:136-143), which examined U.S. Renal Data System data regarding short-term survival in 151,027 obese new-start dialysis patients. After controlling for demographics and comorbidities, results from this retrospective cohort indicate that obesity is independently associated with reduced all-cause mortality.
These results confirmed findings of an earlier study by Port et al (J Am Soc Nephrol. 2002;13:1061-1066), which followed survival data of 45,967 incident dialysis patients. The study demonstrated that small body size is an independent risk factor for mortality (42% higher in low vs. high BMI).