An essential water-soluble antioxidant vitamin that drives collagen synthesis, immune defense, and non-heme iron absorption.
What it is
Vitamin C (L-ascorbic acid) is an essential water-soluble ketolactone and potent antioxidant. Humans lack L-gulonolactone oxidase and cannot synthesize vitamin C endogenously. In dietary supplements, it is supplied as pure L-ascorbic acid or buffered mineral ascorbates (calcium or sodium ascorbate) for gentle gastric tolerance. Vitamin C acts as an electron donor, reducing free radicals and serving as an obligate cofactor for prolyl and lysyl hydroxylase enzymes in collagen formation.
Also known as: Ascorbic Acid, L-Ascorbate, Sodium Ascorbate
What it does
- Acts as a primary water-soluble antioxidant, neutralizing reactive oxygen species.
- Essential cofactor for prolyl hydroxylases in triple-helix collagen cross-linking.
- Enhances non-heme iron solubility and uptake across intestinal enterocytes.
- Supports immune cell function, leukocyte chemotaxis, and phagocytic pathogen killing.
Amplified by probiotics
Vitamin C and gut probiotics engage in a powerful biochemical cross-protection loop. Vitamin C acts as a reducing agent in the intestinal lumen, scavenging molecular oxygen and lowering redox potential. This anaerobic, reduced microenvironment directly enhances the survival, colonization, and metabolic activity of oxygen-sensitive Bifidobacterium and Lactobacillus strains. In return, live probiotics produce short-chain fatty acids that lower luminal pH, stabilizing ascorbic acid against oxidative degradation. Furthermore, vitamin C enhances non-heme iron reduction (Fe3+ to Fe2+) for enterocyte transport via SVCT-1, while probiotics protect the epithelial brush border against iron-induced free radical damage.
Typical dose
75–1,000 mg/day
The evidence
Evidence: strongComprehensive meta-analyses and clinical trials demonstrate that vitamin C supplementation shortens upper respiratory infection duration, enhances connective tissue repair, and markedly increases intestinal non-heme iron absorption (Carr & Maggini 2017, Nutrients; Hemilä & Chalker 2013, Cochrane Database Syst Rev).
Safety & who should check first
Tolerable Upper Intake Limit is 2,000 mg/day for adults. Intakes above 2,000 mg/day may cause osmotic diarrhea, nausea, or abdominal cramping.