Vitamin C vs pre-leukemia: the first real trial.

Claim

VITAMIN C VS PRE-LEUKEMIA?

Catch

SMALL PHASE 2

Verdict

A CLUE, NOT A CURE

"Vitamin C fights cancer" has been claimed for fifty years. The EVITA trial is the first randomized, double-blind, placebo-controlled test of oral vitamin C in people with precancerous blood disorders. 109 adults in Denmark and the US — with clonal cytopenia of undetermined significance (CCUS), low-risk myelodysplastic syndromes (MDS), or related conditions — took either 1,000 mg of vitamin C or a placebo daily for 12 months, then were followed for years. Median age was around 73–75, and none were receiving cancer treatment during the study. The primary endpoint failed: the growth rate of the abnormal blood cells was essentially identical between groups (difference −0.016 per year, 95% CI −0.096 to 0.064, p = 0.70). But there were secondary signals. Serious adverse events were less common with vitamin C: 18 of 55 patients (33%) versus 30 of 53 (57%) on placebo — with anemia, pneumonia and internal bleeding less frequent on the vitamin, though gut side effects (diarrhea, esophagitis, gastrointestinal infections) were more frequent, and one kidney-stone case required intervention. Vitamin C also changed inflammatory cytokine trajectories in ways the authors link to better outcomes. The headline result is the survival gap: at a median follow-up of 33.6 months, 11 deaths in the vitamin C group versus 24 in the placebo group, with median overall survival not reached versus 42.2 months (hazard ratio 0.35, 95% CI 0.17–0.71, p = 0.0025). The catch: overall survival was a post hoc, exploratory endpoint — the trial was neither powered nor designed to measure survival — and it was a small phase 2 study with no formal sample-size calculation. The adjusted analysis (HR 0.42) held up after accounting for baseline imbalances, but the authors themselves call this hypothesis-generating and want a phase 3 trial before anyone changes practice. This was studied in sick, older patients with blood disorders — it is not evidence that vitamin C prevents cancer in the general population.

SOURCES

1. Mikkelsen, S. U., et al. (2026), "Oral vitamin C supplementation in patients with clonal cytopenia of undetermined significance or lower-risk myeloid malignancies: Results from EVITA, a phase 2 randomized, placebo-controlled trial," Cancer, 132(19), e70549. DOI: 10.1002/cncr.70549
2. ClinicalTrials.gov NCT03682029 (EVITA trial registration)
3. Van Andel Institute / Wiley press release (September 21, 2026), "Can vitamin C improve outcomes in people with pre-cancer blood disorders?"
4. ScienceDaily (October 20, 2026), "Scientists discover a surprising link between vitamin C and cancer survival"

For information only, not medical advice. If you have a blood disorder or take supplements and have health concerns, talk to your doctor before changing anything.