Vitamin C

Hemilä and Chalker (Cochrane Database Syst Rev, 2013; PMID 23440782) pooled 31 placebo-controlled comparisons with 9,745 cold episodes: taking vitamin C every day shortened colds by 8 percent in adults (95% CI 3 to 12) and 14 percent in children (7 to 21), roughly half a day on a week-long cold in an adult. Hemilä and Chalker (BMC Public Health, 2023; PMID 38082300) pooled 15 comparisons from 10 randomized, double-blind Neither the participants nor the people assessing them know who received the real treatment until the trial ends. trials at 1 g a day or more and found colds 15 percent less severe (9 to 21). Many independent trials, consistent in direction, on a self-reported endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score., which caps the letter at B. The effect is small, and it applies only to vitamin C taken every day before the cold starts.

Hemilä and Chalker (Cochrane Database Syst Rev, 2013; PMID 23440782): in the 7 comparisons where vitamin C was started after the cold began, there was no consistent effect on how long the cold lasted or how bad it was. Tested, no benefit.

Hemilä and Chalker (Cochrane Database Syst Rev, 2013; PMID 23440782): in general community trials with 10,708 participants, the chance of catching a cold was the same on vitamin C and placebo (risk ratio 0.97, 95% CI 0.94 to 1.00). Tested, no benefit.

Hemilä and Chalker (Cochrane Database Syst Rev, 2013; PMID 23440782): in 5 trials with 598 marathon runners, skiers and soldiers on subarctic exercises, colds were about half as common on vitamin C (risk ratio 0.48, 95% CI 0.35 to 0.64). The trials are small and the outcome is self-reported, so the letter stays at C.

Physicians' Health Study II (Sesso et al., JAMA, 2008; PMID 18997197): 14,641 men, 500 mg a day for a mean 8 years; major cardiovascular events unchanged (hazard ratio How often an event happened in the treated group compared with the control group over the same period. A ratio of 0.80 means 20 percent fewer events. 0.99, 0.89 to 1.11), and total mortality unchanged (1.07, 0.97 to 1.18). Women's Antioxidant Cardiovascular Study (Cook et al., Arch Intern Med, 2007; PMID 17698683): 8,171 women at high risk, 500 mg a day for a mean 9.4 years; no effect on the combined outcome (relative risk The risk in one group expressed as a share of the risk in another. It can make a small absolute difference look large. 1.02, 0.92 to 1.13). Two large trials in men and women, both null: tested, no benefit.

Physicians' Health Study II (Gaziano et al., JAMA, 2009; PMID 19066368): 14,641 men, 500 mg a day for a mean 8 years; total cancer (hazard ratio 1.01, 0.92 to 1.10) and prostate cancer (1.02, 0.90 to 1.15) unchanged. Women's Antioxidant Cardiovascular Study (Lin et al., J Natl Cancer Inst, 2009; PMID 19116389): 7,627 women, 500 mg a day for an average 9.4 years; total cancer relative risk 1.11 (0.95 to 1.30) and cancer death 1.28 (0.95 to 1.73), neither significant. Two large trials, both null: tested, no benefit.

Juraschek et al. (Am J Clin Nutr, 2012; PMID 22492364) pooled 29 randomized trials, median 500 mg a day for a median 8 weeks, each with 10 to 120 participants: systolic pressure fell 3.84 mmHg (95% CI 2.38 to 5.29) and diastolic 1.48 mmHg. Kosari et al. (Food Funct, 2026; PMID 41784995) re-pooled 17 trials and found about 3.7 mmHg lower systolic pressure, rating the certainty low. Blood pressure is an established stand-in for heart attack and stroke, but every trial is small and short, which holds the letter at C.

Juraschek et al. (Am J Clin Nutr, 2022; PMID 35575611) went back to the Physicians' Health Study II after it ended: men assigned 500 mg a day reported 12 percent fewer new gout diagnoses (hazard ratio 0.88, 0.77 to 0.99). It was an analysis added after the trial, on a self-reported diagnosis, in one trial. In people who already had gout, Stamp et al. (Arthritis Rheum, 2013; PMID 23681955) found 500 mg a day for 8 weeks lowered uric acid by only 0.23 mg/dL, against 1.9 mg/dL for allopurinol. One positive analysis nobody has repeated: C.

Zollinger et al. (Lancet, 1999; PMID 10636366): 123 adults with wrist fractures, 500 mg a day for 50 days; the pain syndrome then called reflex sympathetic dystrophy occurred in 7 percent of wrists on vitamin C against 22 percent on placebo. Zollinger et al. (J Bone Joint Surg Am, 2007; PMID 17606778), the same group: 416 patients, 2.4 percent against 10.1 percent, with 500 and 1,500 mg a day both effective. Ekrol et al. (J Bone Joint Surg Am, 2014; PMID 25187584), an independent group: 336 patients, 500 mg a day for 50 days, no difference in the syndrome, function or healing at one year. Evaniew et al. (J Orthop Trauma, 2015; PMID 26197022) pooled the three trials, 890 patients: risk ratio 0.45 (0.18 to 1.13), not significant, with low-quality evidence. Positive in one group's trials, null when an independent group repeated it: C.

LOVIT (Lamontagne et al., N Engl J Med, 2022; PMID 35704292): 872 adults with sepsis on vasopressors; death or persistent organ dysfunction at 28 days in 44.5 percent on vitamin C against 38.5 percent on placebo (risk ratio 1.21, 1.04 to 1.40). CITRIS-ALI (Fowler et al., JAMA, 2019; PMID 31573637): 167 adults with sepsis and lung failure; no difference in the organ failure score. C-EASIE (Vandervelden et al., Crit Care, 2025; PMID 40269974): 300 emergency department patients, 1.5 g every 6 hours for 4 days; organ failure 8.7 percent lower, not significant. The largest trial found harm, the others found no benefit: tested, harm found. This is a hospital treatment and says nothing about vitamin C tablets.

VICTORY (Stoppe et al., JAMA, 2026; PMID 42267875): 238 adults with severe burns. Death or persistent organ dysfunction at 28 days occurred in 40.8 percent on vitamin C against 29.7 percent on placebo (risk ratio 1.28, 0.99 to 1.65, P = .06), which crossed the trial's stopping threshold. Death within 28 days was higher on vitamin C, 15.0 against 7.6 percent (risk ratio 1.96, 1.32 to 2.90), and hospital death 23.3 against 16.1 percent. A hospital treatment, tested and possibly harmful; it says nothing about vitamin C tablets.