Researchers from the University of California (UC), San Diego, and collaborators conducted a cross-sectional analysis of 567 older men quantifying serum vitamin D metabolites using LC-MSMS and defining stool sub-Operational Taxonomic Units from16S ribosomal RNA gene sequencing data, determining that serum 1,25(OH)₂D correlated strongly with high microbiome diversity, generally associated with better health outcomes.