Effect of vitamin D supplementation on serum C-reactive protein level: a meta-analysis of randomized controlled trials

Objective: Vitamin D may have anti-inflammatory actions; however, there is no consensus on the effects of vitamin D supplementation on C-reactive protein (CRP) level in randomized clinical trials (RCTs). In a systematic review and meta-analysis, we investigated the effect of vitamin D supplementation on serum CRP levels. Methods: A systematic search for RCTs was conducted on PubMed, and Scopus, and completed by a manual review of the literature from January 2000 to May 2015. The pooled effect was estimated using a random-effects model and the statistical heterogeneity was assessed by Cochran’s Q and I2 statistics. Results: Of 157 potentially relevant studies retrieved, 20 clinical trials met the inclusion criteria. Mean baseline CRP levels in the intervention and the control groups were 3.5 ± 2.6 and 3.3 ± 2.3 mg/L, respectively. The mean duration of the studies was 29.0  ±  30.2.0 weeks (8 to 144 weeks). The dose of vitamin D3 supplementation varied between 200 and 57142 IU/day. Pooled analysis showed a nonsignificant increase of 0.04 mg/L (95% CI, −0.12 to 0.21; p = 0.61), with no evidence of heterogeneity (I2 = 17.8%, p = 0.17). Conclusion: Vitamin D supplementation may not be effective in reducing CRP. However, a more accurate estimate of the effect requires further large and well-designed clinical trials.