Vitamin D metabolites and risk of first clinical diagnosis of central nervous system demyelination.

Low 25-hydroxyvitamin D (25(OH)D) concentration is a recognised risk factor for multiple sclerosis (MS). Associations with vitamin D metabolites and vitamin D binding globulin (VDBG) have not been widely studied. We assessed the association between vitamin D metabolites (25(OH)D, 25(OH)D, c3-epimer 25(OH)D, 1,25-dihydroxyvitamin D (1,25(OH)D), and 24,25-dihydroxyvitamin D (24,25(OH)D)) measured by liquid chromatography-tandem mass spectrometry assays, VDBG measured using a polyclonal immunoassay, and calculated free and bioavailable 25(OH)D, free 1,25(OH)D, and the 24,25(OH)D: total 25(OH)D and total 1,25(OH)D: total 25(OH)D ratios with risk of a first clinical diagnosis of CNS demyelination (FCD) in an Australian case-control study (n = 196 cases, n = 241 controls, matched on age, sex and study region).