1,000 mg of Vitamin C a Day: What a New Trial Really Found

More than half the participants in a new clinical trial walked in vitamin C-deficient. After a year of a simple over-the-counter supplement, their levels normalized — and over nearly three years of follow-up, notably fewer of them had died than in the placebo group. Could a plain 1,000-mg vitamin C tablet help intercept blood cancer before it starts? Here’s what the study actually found, what it didn’t, and what it means for Canadians.

The EVITA Trial at a Glance

What the EVITA Trial Found — and What It Didn’t

The EVITA trial was a phase 2 randomized, double-blind, placebo-controlled study — the gold standard of clinical research — involving 109 people with clonal cytopenia of undetermined significance (CCUS) or myelodysplastic syndrome (MDS). These are pre-cancerous blood disorders that can progress to acute myeloid leukemia (AML), and there are currently no approved therapies that prevent that progression. The trial ran at hospitals in Denmark (Rigshospitalet, Herlev, Aalborg) and at USC’s Keck Hospital in California, and the results were published in CANCER, the American Cancer Society’s journal, on September 21, 2026.

On the trial’s primary goal, the results were a miss: vitamin C did not significantly slow the growth of abnormal blood-cell clones, the standard marker of progression toward leukemia. But the secondary findings are what caught researchers’ attention:

There’s a plausible biological mechanism behind this. Vitamin C is an essential cofactor for TET2, an enzyme that regulates whether certain genes are switched “on” or “off” and acts as a brake on malignant blood-cell growth — mutations in TET2 are a common feature of leukemia and related disorders. Earlier laboratory work had suggested vitamin C’s benefit is greatest when supplementation begins before disease is established, which is exactly what this trial tested. The researchers stressed that the survival finding was exploratory and must be confirmed in a larger phase 3 trial before treatment recommendations change — but they called the results a strong rationale to keep going.

The Supplement Connection: Vitamin C, Blood Health, and Sensible Doses

Before anyone raids the supplement aisle, note what this trial does and doesn’t prove. It studied people with specific blood disorders under medical supervision — not the general population. That said, for anyone who already supplements, here’s how the evidence maps to the products on shelves:

• Vitamin C (ascorbic acid) — the workhorse form. Vitamin C acts as an antioxidant, supports immune function, wound healing and collagen formation, and helps the body absorb iron from plant foods. The EVITA trial used plain oral ascorbic acid, exactly the form sold in most drugstores. Health Canada’s recommended dietary allowances are 90 mg per day for adult men and 75 mg for adult women — amounts most people can get from food — while common over-the-counter products provide 500–1,000 mg per capsule. The trial dose was 1,000 mg per day; Health Canada’s tolerable upper intake level is 2,000 mg per day, so don’t go above that without medical guidance.
• Buffered and slow-release vitamin C formulas — these use mineral ascorbates (like calcium or sodium ascorbate) or time-release matrices marketed as gentler on the stomach. Given that the vitamin C group in the trial reported more gastrointestinal issues at 1,000 mg, these formats may be a reasonable comfort choice if standard ascorbic acid bothers you. Be aware that evidence they work better than plain ascorbic acid is limited — this is about tolerability, not extra efficacy.
• Vitamin C with bioflavonoids — a common formulation pairing vitamin C with plant compounds claimed to support absorption. There is no strong evidence these outperform ascorbic acid alone, and they weren’t what the trial used. If you buy one, judge it on price and dose, not the marketing.

The Canadian Angle: NPN Labels, Label Rules, and Where to Buy

In Canada, vitamin C products sold with health claims are regulated as natural health products, and legal ones carry an eight-digit Natural Product Number (NPN) on the label — a signal that Health Canada has assessed the product for safety, quality and the claimed use. The EVITA trial’s 1,000-mg dose matches products already widely available here, but remember: the study involved diagnosed patients, not shoppers looking for general wellness, so don’t treat it as a do-it-yourself treatment protocol.

• Always look for the NPN on the label before buying any vitamin C product in Canada.
• Buy from licensed Canadian pharmacies and established retailers — Shoppers Drug Mart, Rexall, Costco, or reputable health-food stores — rather than grey-market import listings where label claims and content can’t be verified.
• Health Canada’s natural health product labelling rules are being modernized, with full compliance required by June 2028 — upcoming label changes should make it easier to compare doses and check what actually is in the bottle.
• If you take vitamin C at higher doses, mention it to your pharmacist or doctor, since even simple supplements can interact with certain medications and lab tests.

Your Next Steps

This trial is a promising first step, not a prescription — watch for a larger phase 3 study before expecting anything to change in medical practice. In the meantime, if you rarely eat fruit and vegetables, ask your healthcare provider whether a vitamin C blood test makes sense for you, and if you do supplement, choose an NPN-licensed product at a sensible dose and mention it at your next checkup.

This article reports on recent health research and is for general information only — it isn’t medical advice and doesn’t replace your doctor, pharmacist, or another qualified professional. Study findings describe what researchers observed, not a promise of results, and nothing here claims any supplement can diagnose, treat, cure, or prevent a disease. These statements have not been evaluated by Health Canada. Check with a healthcare professional before starting any new supplement, especially if you’re pregnant, nursing, taking medication, or managing a health condition.