A Cross-sectional Evaluation of the Relationship Between Vitamin D Status and Supplement Use Across Levels of Kidney Function in Adults: Vitamin D Status, Supplements, and Kidney function

Objectives: The objective of this study was to assess vitamin D status of US non-pregnant adults using a standardized assay across 15mL/min/1.73m2 increments of kidney function, report the use of dietary supplements containing vitamin D, and assess relationships between vitamin D and markers of bone resorption. Design: This study is a cross-sectional evaluation Setting: The study is from the United States National Health and Nutrition Evaluation Survey in 2001-2012 Participants: The participants were non-institutionalized, non-pregnant adults, age ≥20 years.Primary and secondary outcome measures: The primary outcome measure was serum 25OHD evaluated using liquid chromatography-tandem mass spectroscopy traceable to international reference standards. Secondary outcome measures were use of dietary supplements containing vitamin D and the serum intact parathyroid hormone and bone-specific alkaline phosphatase in a sub-set of participants. Results: The median 25OHD concentration in 27,543 US non-pregnant adults was 25.7ng/mL (range, 2.2-150.0ng/mL). Vitamin D supplements were used by 38.0%; mean (SE) = 757 (43) IU/day. The range of 25OHD concentration across groups, stratified by kidney function, was 23.0-28.1 ng/mL. The lowest concentration of 25OHD observed was in people with higher kidney function (23.0ng/mL for estimated Glomerular Filtration Rate >105mL/min/1.73m2). Only 24% of people not taking a dietary supplement had a 25OHD concentration >30 ng/mL. Serum iPTH inversely correlated with 25OHD within all kidney function groups. Bone-specific alkaline phosphatase was also negatively associated with 25OHD concentration. Conclusions: These data indicate that 25OHD concentrations and supplement suboptimal in a significant proportion of the population, across all kidney function levels. The response of bone resorption markers further suggests that 25OHD levels could be improved. Together, these data support a reevaluation of the 25OHD concentration associated with health in adults.