Pilot Trial of Vitamin D3 and Calcifediol in Healthy Vitamin D Deficient Adults: Does It Change the Fecal Microbiome?

Context Experimental studies suggest that vitamin D receptor signaling may benefit the gut microbiome. In humans, whether vitamin D supplementation directly alters the gut microbiome is not well studied. Objective To determine whether correcting vitamin D deficiency with cholecalciferol (vitamin D3, D3) or calcifediol (25-hydroxyvitamin D3, 25(OH)D3) changes gut microbiome composition. Methods 18 adults with vitamin D deficiency (25-hydroxyvitamin D [25(OH)D] <20 ng/mL) received 60 mu g/day of D3 or 20 mu g/day of 25(OH)D3 for 8 weeks. Changes in serum 25(OH)D, 1,25-diydroxyvitamin D (1,25(OH)(2)D), and 24,25-dihydroxyvitamin D (24,25(OH)(2)D) were assessed. We characterized composition of the fecal microbiota using 16S rRNA gene sequencing, and examined changes in alpha-diversity (Chao 1, Faith's Phylogenetic Diversity, Shannon Index), beta-diversity (DEICODE), and genus-level abundances (DESeq2). Results Vitamin D3 and 25(OH)D3 groups were similar. After 8 weeks of vitamin D3, mean 25(OH)D and 24,25(OH)(2)D increased significantly, but 1,25(OH)(2)D did not (25(OH)D: 17.8-30.1 ng/mL, P = .002; 24,25(OH)(2)D: 1.1 to 2.7 ng/mL, P =0.003; 1,25(OH)(2)D: 49.5-53.0 pg/mL, P = .9). After 8 weeks of 25(OH)D3, mean 25(OH)D, 24,25(OH)(2)D, and 1,25(OH)(2)D increased significantly (25(OH)D: 16.7-50.6 ng/mL, P < .0001; 24,25(OH)(2)D: 1.3-6.2 ng/mL, P = .0001; 1,25(OH)(2)D: 56.5-74.2 pg/mL, P = .05). Fecal microbial alpha-diversity and beta-diversity did not change with D3 or 25D3 supplementation. Mean relative abundance of Firmicutes increased and mean relative abundance of Bacterioidetes decreased from baseline to 4 weeks, but returned to baseline by study completion. DESeq2 analysis did not confirm any statistically significant taxonomic changes. Conclusion In a small sample of healthy adults with vitamin D deficiency, restoration of vitamin D sufficiency with vitamin D3 or 25(OH)D3 did not lead to lasting changes in the fecal microbiota.