Vitamin C supplementation and C-reactive protein levels: Findings from a systematic review and meta-analysis of clinical trials.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of clinical trials
PubMed 32229693 · doi:10.1515/jcim-2019-0151
What was done
A systematic review and meta-analysis of clinical trials published through August 2018 was conducted across PubMed, Scopus, Ovid, ISI Web of Science, Embase, and Cochrane databases. The analysis evaluated the effects of vitamin C supplementation or vitamin C-enriched foods versus placebo on C-reactive protein (CRP) and high-sensitivity CRP (hs-CRP) levels. A total of 11 studies with 14 datasets involving 818 participants were included.
What was found
Vitamin C supplementation significantly decreased CRP levels compared to placebo (weighted mean difference [WMD] = -0.73 mg/L, 95% CI: -1.30 to -0.15, p = 0.013), though heterogeneity was extreme (I2 = 98%, p < 0.001). In subgroup analyses, significant reductions in CRP were limited to males (p = 0.003), non-smokers (p = 0.041), healthy individuals (p = 0.029), younger participants (p = 0.010), and doses under 500 mg/day (p = 0.009). For hs-CRP, pooled analysis showed no significant effect (WMD = -0.65 mg/L, 95% CI: -2.03 to 0.72, p = 0.35), but hs-CRP was significantly elevated after vitamin C supplementation in a subgroup analysis of high-quality studies (p = 0.026).
Why it matters
This review suggests vitamin C may modestly lower standard CRP in specific subgroups at lower doses, but does not reliably lower hs-CRP and may have inconsistent effects depending on trial quality.
Limits
The total sample size was small (818 participants across 11 trials), and statistical heterogeneity for the primary outcome was extremely high (I2 = 98%). The unexpected finding of increased hs-CRP in high-quality trials weakens confidence in a true anti-inflammatory benefit.
Cited by
- context Supplementing with 2 grams of vitamin C per day lowers C-reactive protein levels.