Mortality Rates Across 25-Hydroxyvitamin D (25[OH]D) Levels among Adults with and without Estimated Glomerular Filtration Rate <60 ml/min/1.73 m2: The Third National Health and Nutrition Examination Survey

Background

Previous studies exploring the association between 25OH]D levels and mortality in adults with and without kidney disease utilized 25OH]D thresholds that have recently been scrutinized by the Institute of Medicine Committee to Review Dietary References Intakes for Vitamin D and Calcium.

Objective

We explored all-cause mortality rates across the spectrum of 25OH]D levels over an eighteen-year follow-up among adults with and without an estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m².

Design

The study included 1,097 U.S. adults with eGFR <60 ml/min/1.73 m² and 14, 002 adults with eGFR ≥60 ml/min/1.73 m². Mortality rates and rate ratios (RR) across 25OH]D groups were calculated with Poisson regression and restricted cubic splines while adjusting for covariates.

Results

Prevalence of 25OH]D levels <30 and <20 ng/ml among adults with eGFR <60 ml/min/1.73 m² was 76.5% (population estimate 6.2 million) and 35.4% (population estimate 2.9 million), respectively. Among adults with eGFR ≥60 ml/min/1.73 m², 70.5% had 25OH]D levels <30 ng/ml (population estimate 132.2 million) while 30.3% had 25OH]D levels <20 ng/ml (population estimate 56.8 million). Significantly higher mortality rates were noted among individuals with 25OH]D levels <12 ng/ml compared to referent group (24 to <30 ng/ml): RR1.41 (95% CI 1.17, 1.71) among individuals with eGFR <60 ml/min/1.73 m² and RR 1.32 (95% CI 1.13, 1.56) among individuals with eGFR ≥60 ml/min/1.73 m² after adjustment for covariates including co-morbid conditions. Mortality rates were fairly similar across all 25OH]D groups with levels >20 ng/ml after adjustment for all covariates.

Conclusions

Regardless of presence of eGFR <60 ml/min/1.73 m², mortality rates across groups with 25OH]D levels 20–40 ng/ml are similar.