Background: This review is an update of a previously published review in the Cochrane Database of Systematic Reviews (Issue 1, 2010) on 'Vitamin D for the treatment of chronic painful conditions in adults'.Vitamin D is produced in the skin after exposure to sunlight and can be obtained through food. Vitamin D deficiency has been linked with a range of conditions, including chronic pain. Observational and circumstantial evidence suggests that there may be a role for vitamin D deficiency in the aetiology of chronic painful conditions.
Objectives: To assess the efficacy and safety of vitamin D supplementation in chronic painful conditions when tested against placebo or against active comparators.
Search methods: For this update, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE to February 2015. This was supplemented by searching the reference lists of retrieved articles, reviews in the field, and online trial registries.
Selection criteria: We included studies if they were randomised double-blind trials of vitamin D supplementation compared with placebo or with active comparators for the treatment of chronic painful conditions in adults.
Data collection and analysis: Two review authors independently selected the studies for inclusion, assessed methodological quality, and extracted data. We did not undertake pooled analysis due to the heterogeneity of the data. Primary outcomes of interest were pain responder outcomes, and secondary outcomes were treatment group average pain outcomes and adverse events.
Main results: We included six new studies (517 participants) in this review update, bringing the total of included studies to 10 (811 participants). The studies were heterogeneous with regard to study quality, the chronic painful conditions that were investigated, the dose of vitamin D given, co-interventions, and the outcome measures reported. Only two studies reported responder pain outcomes; the other studies reported treatment group average outcomes only. Overall, there was no consistent pattern that vitamin D treatment was associated with greater efficacy than placebo in any chronic painful condition (low quality evidence). Adverse events and withdrawals were comparatively infrequent, with no consistent difference between vitamin D and placebo (good quality evidence).
Authors' conclusions: The evidence addressing the use of vitamin D for chronic pain now contains more than twice as many studies and participants than were included in the original version of this review. Based on this evidence, a large beneficial effect of vitamin D across different chronic painful conditions is unlikely. Whether vitamin D can have beneficial effects in specific chronic painful conditions needs further investigation.