vitamin · for frequent colds
Vitamin C
Your immune cells use vitamin C to hunt down and destroy invaders.
Say that in clinical terms
Vitamin C supports immune function by enhancing neutrophil chemotaxis, phagocytosis, and reactive oxygen species generation. It also supports epithelial barrier function, increases natural killer cell activity, and modulates T-cell maturation.
How strong is the research?
A Cochrane review of over 11,000 people: it does not stop you catching colds, though it may shorten one slightly.
3 papers read, 1 supporting, 2 against.
Who was studied: The big effect — about half the colds — was only in marathon runners, skiers and soldiers under heavy physical stress.
How much to take
daily (increase to 2000mg during illness)
500–1000 mg
Take daily for prevention. Increase dose at first sign of symptoms. Divide doses throughout the day for better absorption.
Before you take it
- NIH ODS Tolerable Upper Intake Level (UL) for adults is 2,000 mg/day (combined dietary and supplemental intake)
- GI distress (osmotic diarrhea, nausea, abdominal cramping) commonly occurs above 1,000 mg/day due to unabsorbed ascorbic acid reaching the colon
- Sustained high-dose supplementation increases risk of calcium oxalate kidney stones; particular caution warranted in individuals with prior nephrolithiasis or hyperoxaluria
- Vitamin C markedly enhances non-heme iron absorption; supplemental doses are contraindicated in hemochromatosis and other iron-overload conditions
- High-dose Vitamin C antioxidant activity may attenuate the efficacy of chemotherapy and radiation therapy; per NIH ODS, consultation with an oncologist is required before supplementing during active cancer treatment
- High-dose Vitamin C combined with antioxidant mixtures (including vitamin E, beta-carotene, selenium) may blunt the HDL-raising effect of niacin-statin combination therapy per NIH ODS
What we make of it
The Cochrane review is routinely misread. Its actual finding on prevention is null.
The detail
This review gets quoted as support for vitamin C preventing colds. Its actual primary finding in ordinary adults is that it does not — no meaningful reduction in how often people catch one. What it does support is a small shortening of a cold once you have it, and a real prevention effect in people under extreme physical stress.