Low circulating 25-hydroxyvitamin D (25(OH)D) levels have been associated with an increased risk of relapses in relapsing remitting multiple sclerosis (RRMS), but an association with disability progression is uncertain. Lower 25(OH)D levels are found in secondary progressive MS (SPMS) when compared to RRMS. We hypothesized that a poor vitamin D status in RRMS is associated with an increased risk of conversion to SPMS. In a retrospective longitudinal study we measured 25(OH)D levels at the start of a 3-year follow-up, and analyzed whether these levels predict the risk of RRMS to SPMS conversion. In 338 RRMS patients, vitamin D status did not predict the 3-year risk of conversion to SPMS (n=51; OR 0.970; p=0.65). However, in diagnostic blood samples of SPMS patients with a relatively short RRMS duration (n=19) 25(OH)D levels were significantly lower (38nmol/L; Q1-Q3: 24-50) than in diagnostic samples of matched RRMS patients with no progression to SPMS ((n=38; 55nmol/L; Q1-Q3: 40-70) (p<0.01). These data indicate an association between a low vitamin D status at the start of RRMS and the early conversion to SPMS. Therefore, time to SPMS conversion is of interest as clinical measure in (follow-up of) clinical vitamin D supplementation studies.
Keywords: 25-Hydroxyvitamin D; Disability; Relapsing remitting multiple sclerosis; Secondary progressive multiple sclerosis; Vitamin D.
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