Vitamin C and Immune Function.
Level 5 - mechanism / opinion, no new human data
Narrative review of biological mechanisms and clinical concepts without a systematic search or meta-analysis protocol
PubMed 29099763 · doi:10.3390/nu9111211
What was done
This narrative review summarizes the biochemical mechanisms and clinical roles of vitamin C in the human immune system. It examines the micronutrient's impact on epithelial barriers, cellular functions of innate immunity (such as neutrophil chemotaxis, phagocytosis, and clearance), adaptive lymphocyte proliferation, and the physiological rationale for prophylactic versus therapeutic dosing in infections.
What was found
The abstract reports mechanistic pathways and recommended intake targets rather than empirical trial statistics. Vitamin C accumulates in phagocytes to enhance microbial killing and subsequent apoptotic clearance, and aids B- and T-cell differentiation. Deficiency impairs immunity and increases infection susceptibility, while active infection depletes vitamin C levels. Prophylactic prevention of infection requires 100–200 mg/day to achieve saturating plasma and tissue levels, whereas treating established respiratory or systemic infections requires gram-level doses to match increased metabolic demand. Specific numerical trial outcomes and effect sizes are not reported in the abstract.
Why it matters
It outlines how vitamin C functions across multiple branches of the immune system and clarifies why baseline nutritional adequacy differs from the higher doses required during active infection.
Limits
The abstract describes a narrative overview rather than a systematic review or meta-analysis, providing no study selection criteria, sample sizes, or risk-of-bias evaluations. Quantitative effect sizes, specific patient cohorts, and safety profiles of high-dose regimens are not detailed in the abstract.
Cited by
- supports Neutrophils and leukocytes have vitamin C concentrations between 50 to 100 times higher than plasma.
- supports Studies in guinea pigs suggest that vitamin C plays an important role in facilitating neutrophil migration to sites of infection.