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Vitamin D and its main active metabolite 1,25-dihydroxyvitamin D serve a crucial role in maintenance of a healthy calcium metabolism, yet have additional roles in immune and central nervous system cell homeostasis. Serum levels of 25-hydroxyvitamin D are a biomarker of future disease activity in patients with early relapsing-remitting multiple sclerosis (RRMS), and vitamin D supplementation in patients with low circulating 25-dihydroxyvitamin D levels has been anticipated as a potential efficacious treatment strategy. The results of the first large randomized clinical trials (RCTs), the SOLAR and CHOLINE studies, have now been published. The SOLAR study compared 14,000 IU of vitamin D3 (cholecalciferol) per day with placebo for 48 weeks in 232 randomized patients, whereas CHOLINE compared vitamin D3 100,000 IU every other week with placebo for 96 weeks in 129 randomized patients. All patients in both studies also used interferon-β-1a. None of the studies met their primary endpoints, which were no evidence of disease activity (NEDA-3) at 48 weeks in SOLAR and annualized relapse rate at 96 weeks in CHOLINE. Both studies did, however, suggest modest effects on secondary endpoints. Thus, vitamin D reduced the number of new or enlarging lesions and new T2 lesions in SOLAR, and the annualized relapse rate and number of new T1 lesions, volume of hypointense T1 lesions, and disability progression in the 90 patients who completed 96 weeks' follow-up in CHOLINE. We conclude that none of the RCTs on vitamin supplementation in MS have met their primary clinical endpoint in the intention to treat cohorts. This contrasts the observation studies, where each 25 nmol/l increase in 25-hydroxyvitamin D levels were associated with 14-34% reduced relapse risk and 15-50% reduced risk of new lesions on magnetic resonnance imaging. This discrepancy may have several explanations, including confounding and reverse causality in the observational studies. The power calculations of the RCTs have been based on the observational studies, and the RCTs may have been underpowered to detect less prominent yet important effects of vitamin D supplementation. Although the effect of vitamin D supplementation is uncertain and less pronounced than suggested by observational studies, current evidence still support that people with MS should avoid vitamin D insufficiency, and preferentially aim for vitamin D levels around 100 nmol/L or somewhat higher. [ABSTRACT FROM AUTHOR]

Observational studies have suggested that vitamin D may reduce inflammation in relapsing-remitting multiple sclerosis (RRMS), but this has not been clearly confirmed in randomized controlled trials. To further explore the possible anti-inflammatory effects of vitamin D in RRMS, we examined the effect of high-dose oral vitamin D on eleven markers of systemic inflammation in 68 RRMS patients enrolled in a double-blinded randomized placebo-controlled trial of vitamin D supplementation (20,000 IU/week) (NCT00785473). Serum inflammation markers and 25-hydroxyvitamin D (25(OH)D) were measured at baseline and week 96, and no restrictions were set on additional standard immunomodulatory treatment for RRMS. The mean 25(OH)D level rose from 56 ± 29 to 123 ± 34 nmol/L among patients receiving vitamin D supplementation, whereas only a minor increase from 57 ± 22 to 63 ± 24 nmol/L was seen in the placebo group. However, no significant differences appeared between the vitamin D group and the placebo group for any of the inflammation markers. Patients on immunomodulatory therapy had significantly higher levels of interleukin-1 receptor antagonist and chemokine (C-X-C motif) ligand 16 than patients without immunomodulatory treatment, but there were no clear synergistic effects between immunomodulatory therapy and vitamin D supplementation on any of the inflammation markers. The rise in 25(OH)D levels after vitamin D supplementation was unaffected by immunomodulatory treatment. We conclude that in this study of RRMS patients, high-dose oral vitamin D supplementation prominently increased serum 25(OH)D levels without affecting markers of systemic inflammation, while a more anti-inflammatory phenotype was found among patients on immunomodulatory treatment. [ABSTRACT FROM AUTHOR]