Does 25(OH)D serum level affect renal function?

Increased serum levels of 25-hydroxyvitamin D (25[OH]D) show a significant association with genetically predicted chronic kidney disease (CKD), increased blood urea nitrogen (BUN), and decreased estimated glomerular filtration rate (eGFR), reports a Europe study. However, 25(OH)D appears to have no causal effect on renal function.

The authors conducted this two-sample Mendelian randomization (MR) study and applied single nucleotide polymorphisms (SNP) associated with 25(OH)D in 443,734 Europeans. They also examined its effects on eGFR, BUN, CKD risk and progression in genome-wide association studies among over 1 million Europeans.

SNPs were also used solely in DHCR7, CYP2R1, and GC, all genes with known roles in vitamin D metabolism to control for pleiotropy. Finally, the authors carried out a reverse MR using SNPs for the above indices of renal function to analyse the causal effects of 25(OH)D levels.

No robust evidence could support the effects of 25(OH)D on eGFR, BUN, and CKD or its progression.

On inverse variance weighted MR, a 0.56 decrease was observed in standardized log-transformed 25(OH)D (95 percent confidence interval [CI], ‒0.73 to ‒0.41; p=2.89 x 10^-12) per unit increase in log-transformed eGFR. Increased BUN correlated with higher 25(OH)D (β, 0.25, 95 percent CI, 0.15‒0.36; p=4.12 x 10^-6) per unit increase in log-transformed BUN.

Additionally, genetically predicted CKD showed a 0.05 increase in standardized log-transformed 25(OH)D level (95 percent CI, 0.04‒0.06; p=1.06 x 10^-13).

These findings were confirmed in other MR methods.