Vitamin C (regular use)
Ascorbic acid
Moderate
Some good studies, not many repeats
Moderate: large Cochrane base, but effects are small outside high-physical-stress groups.
Taken every day, it makes colds about 8% shorter in adults, and halves how often people under heavy physical strain catch one. Starting it once you are already sick does little.
Taken regularly — not once symptoms start — vitamin C shortens colds by about 8% in adults and halves the number of colds in people under extreme physical stress like marathoners. Starting it after onset does little.
Antioxidant support for neutrophil and lymphocyte function.
Endurance athletes and people under heavy physical strain. 200–1,000 mg/day.
What to buy
- ✓500–1,000 mg ascorbic acid
- ✕Multi-gram daily doses (kidney-stone risk)
- · Kidney-stone caution at multi-gram chronic doses.
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Regular daily use is what the evidence supports.
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See all on AmazonEvery result, next to the line that means no effect
Each diamond is a study's best estimate. The thin line shows how sure the study was: the shorter the line, the more certain the result.
- Cold duration (adults, regular use)% · Hemilä 2013−8.00%[not given]
- Cold incidence under extreme physical stress% · Hemilä 2013−50.0%[not given]
Each unit gets its own scale, so numbers are never mixed on one line. When a study gave no range, we leave it blank instead of inventing one.
1 studies over 1 years
The studies
- 1.Vitamin C for preventing and treating the common coldCochrane Database of Systematic Reviews · 2013 · systematic review · 29 experiments · n = 11,306
Regular ≥200 mg/day: −8% duration in adults, −14% in children; halved incidence in marathoners/soldiers.
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