Metabolic syndrome and the development of CKD in American Indians: The Strong Heart Study

Background: Metabolic impairments that precede type 2 diabetes, such as metabolic syndrome, may contribute to the development of chronic kidney disease (CKD). This study documents the prevalence and incidence of CKD and the prospective association between metabolic syndrome and CKD in American Indians without diabetes in the Strong Heart Study. Study Design: Prospective cohort study. Setting & Participants: American Indians aged 45 to 74 years from 3 geographic regions were recruited by using tribal records and were assessed every 3 years from 1989 to 1999 as part of the Strong Heart Study. Participants with type 2 diabetes, on dialysis therapy, or who received a kidney transplant at baseline examination were excluded. Predictor: Metabolic syndrome, defined using Adult Treatment Panel III criteria. Outcomes & Measurements: CKD was measured by using estimated glomerular filtration rate (eGFR) and urinary albumin-creatinine ratio (ACR) dichotomized at conventional cutoff values. The association between metabolic syndrome and incident CKD was evaluated by using multivariable Cox proportional hazards models and binomial regression, with statistical adjustment for confounders (age, sex, study center, education, and smoking). Results: Metabolic syndrome was present in 896 (37.7%) and absent in 1,484 participants (62.3%) at baseline. The prevalence of ACR of 30 mg/g or greater at baseline examination was 12.1%, with 290 new cases and an incidence of 233/10,000 person-years. The prevalence of eGFR less than 60 mL/min/1.73 m(2) was 7.8%, with 189 new cases and an incidence of 138/10,000 person-years. The prevalence of CKD was 17.8%, with 388 new cases and an incidence of 342/10,000 person-years. The adjusted hazard ratio for CKD associated with metabolic syndrome was 1.3 (95% confidence interval [CI], 1.1 to 1.6). Equivalent hazard ratios for ACR greater than 30 mg/g and eGFR less than 60 mL/min/1.73 m(2) were 1.4 (95% Cl, 1.0 to 1.9) and 1.3 (95% Cl, 1.0 to 1.6), respectively. The relationship between metabolic syndrome and kidney outcomes was stronger in those who developed diabetes during follow-up. Limitations: Intraindividual variability in serum creatinine and ACR measures may have resulted in some misclassification of participants by outcome status. Conclusions: Metabolic syndrome is associated with an increased risk of developing CKD in American Indians without diabetes. The mechanism through which metabolic syndrome may cause CKD in this population likely is the development of diabetes.