Vitamin C supplementation and C-reactive protein levels: Findings from a systematic review and meta-analysis of clinical trials.

Background and purpose C-reactive protein (CRP) is an inflammatory biomarker which prognosticates cardiovascular disease. Previous studies have reached mixed conclusions regarding the effect of vitamin C on reducing CRP or hs-CRP level. The present systematic review and meta-analysis was conducted to resolve these inconsistencies. Materials and methods: Related articles published up to August 2018 were searched through PubMed, Scopus, Ovid, ISI web of science, Embase, and Cochrane databases by relevant keywords. Clinical trials which examined the effect of either vitamin C supplementation or vitamin C-enriched foods on CRP and hs-CRP levels were included. A total of 11 studies with 14 data sets involving 818 subjects were included. Results Overall, the pooled analysis revealed that vitamin C could decrease CRP level relative to placebo group (Weighted mean difference [WMD]=-0.73 mg/L: 95% CI: -1.30 to -0.15, p=0.013) with a considerable heterogeneity (I2=98%, p<0.001). Moreover, subgroup analyses revealed that the beneficial effect of vitamin C on CRP level alternation only was found in male (p=0.003), non-smoker (p=0.041), healthy (p=0.029) and younger participants (p=0.010). Vitamin C could improve CRP level only at doses of less than 500 mg/day (p=0.009). Regarding hs-CRP changes, the pooled analysis did not show any significant effect of vitamin C (WMD=-0.65 mg/L: 95% CI: -2.03 to 0.72, p=0.35). This finding was confirmed by all subgroup analyses expect for high quality articles in which hs-CRP level was elevated after vitamin C supplementation (p=0.026). Conclusion In conclusion, supplementation with vitamin C might have a significant effect only on CRP reduction. Further studies are needed to confirm this effect.