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Vitamin C

Vitamin C

Best for

Catch fewer colds and infections

Proven strong benefit · 0.05–2000 g/day for 8–14 weeks · 4 meta-analyses , n=36.9k

64 papers · 4 claims · 129 outcomes scored · 4 positive

Evidence summary

Evidence summary

Proven strong benefit

Vitamin C delivers a proven strong benefit for reducing colds and infections in generally healthy people, with the clearest effect coming from regular use rather than treatment after symptoms start.

  • Across 5 studies (n=36,885), vitamin C lowered cold and infection outcomes 1.
  • Vitamin C's broader evidence base spans 64 papers and 129 outcomes across mixed health claims.
  • Benefits are strongest for prevention; treatment of an active cold shows weaker effects.

Outcomes

What vitamin c actually does, by outcome

Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.

Catch fewer colds and infections Proven strong benefit

Your immune barriers intercept more viruses before they take hold.

5 meta-analyses n=37k 0.05–2000 g 8–14 wk #1/17
15495002·23440782·25010554·33472840 +1 more
Raise antioxidant vitamin levels Promising early signal

Vitamin C and E blood levels climb into protective territory.

12 meta-analyses n=711 52–1500 mg 0–16 wk #1/4
18952164·24228847·24838476·25010554 +8 more
Recover from colds faster Faint early signal

Shaves days off a cold by clearing the virus sooner.

6 meta-analyses n=126 1–8000 mg 1–8 wk #5/10
15495002·23440782·25010554·33472840 +2 more
Ease cold and flu severity Not enough research

When you do get sick, the whole experience hits lighter.

6 meta-analyses n=862 1–8000 g 1–8 wk #5/17
15495002·23440782·25010554·33576820 +2 more

Forms & standardisation

The best-studied form is plain vitamin C, meaning ascorbic acid, and the blood-level data also cover buffered salts such as calcium ascorbate 3. Look for the actual milligrams of vitamin C on the label, not just a vague antioxidant blend, because the trials used clear doses you can compare 13.

Risk profile

Adverse events and known drug interactions

Safety events

oxalate nephropathy severe
skin rash severe
Oxalate nephropathy leading to end-stage renal disease severe
kidney stones severe
hypokalemia severe
acute kidney injury severe
oxalate crystal deposition severe
Haemolysis severe

Drug interactions

Bortezomib major decreases effect
Doxorubicin major decreases effect
Warfarin moderate increases effect
Warfarin moderate unknown
Antineoplastic Agents moderate increases effect
Aspirin minor decreases concentration
Atorvastatin minor additive

Co-studied with

Supplements that share evidence with vitamin c

Iron 15 shared outcomes · d=0.17
Drug:Citalopram 8 shared outcomes · d=0.12
Vitamine 5 shared outcomes · d=0.26
Selenium 3 shared outcomes · d=0.24
Molybdenum 1 shared outcome · d=0.03
Vitaminc 1 shared outcome · d=0.33

Frequently asked

Common questions

Can vitamin C prevent colds?

Yes, regular vitamin C lowers the chance of catching a cold, and that benefit shows up much more clearly than its treatment effect once you are already sick 1.

How much vitamin C should I take each day?

Most of the useful trial doses sit around 500–1,000 mg/day, and many of the cold-prevention studies land near 1,000 mg/day 13.

Should I take vitamin C with food?

You do not need food for absorption, but taking it with a meal makes bigger doses easier on your stomach 3.

What form of vitamin C works best?

Plain ascorbic acid has the biggest evidence base. Buffered forms like calcium ascorbate still deliver vitamin C, so the label matters less than the actual milligrams you get 3.

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Sources

  1. 1. Vitamin C for preventing and treating the common cold (2013) ↑
  2. 2. Vitamin C and immune function (2017) ↑
  3. 3. Vitamin C Fact Sheet for Health Professionals

Generated May 15, 2026

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