Associations between Change in Kidney Functioning, Age, Race/ethnicity and Health Indicators in the Health and Retirement Study.

BACKGROUND: The aging process is accompanied by decline in kidney functioning. It remains unknown to what extent age-related decline in kidney functioning can be attributed to health indicators, and whether rate of decline differs across sociodemographic groups.

METHODS: Using data from the Health and Retirement Study from 2006/2008 through 2014/2016, we estimated kidney functioning trajectories, determined by cystatin C, among adults aged over 51 over 8-year. We evaluated the role of age, health conditions/behaviors, and genetics in the decline and also examined sociodemographic differentials.

RESULTS: Kidney function declined with age and accelerated at older ages, even after adjusting for health conditions/behaviors and genetic differences (e.g., 0.019 mg/L annual increase in cystatin C among 70-79 compared to 0.007 mg/L among 52-59 at baseline). Decline occurred faster among those with uncontrolled diabetes (0.008, p=0.009), heart conditions (0.007, p<0.000), and obesity (0.005, p=0.033). Hispanic participants (0.007, p=0.039) declined faster than non-Hispanic White persons due to diabetes, heart conditions, and obesity; non-Hispanic Black participants had worse baseline kidney functioning (0.099, p<0.000), but only one-fourth of this Black-White difference was explained by investigated risk factors. People with higher education experienced slower decline (-0.009, p=0.004).

CONCLUSIONS: Age was a significant predictor of decline in kidney functioning, and its association was not fully explained by health conditions/behaviors, or genetics. Better management of diabetes, heart conditions, and obesity is effective in slowing this decline. Baseline differences in kidney functioning (e.g., between non-Hispanic White and Black persons; those with and without hypertension) suggest disparities occur early in the life course and require early interventions.