A guideline says something specific
Ordinary vitamin C is not the concern. High-dose vitamin C — the kind pushed as an infusion — is a documented cause of severe hemolysis in one specific genotype, and every reported case with that genotype has had it happen.
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G6PD deficiency — see G6PD deficiency — leaves red blood cells short of a key defence against oxidative stress. It is best known for reacting to fava beans and to certain drugs, but vitamin C belongs on that list too, at a dose nobody gets from food or a standard multivitamin.
At pharmacologic doses — grams rather than milligrams, usually given intravenously in cancer-support or "immune boost" contexts rather than taken as a pill — vitamin C acts as a pro-oxidant inside the cell rather than an antioxidant, generating hydrogen peroxide that a normal red cell neutralises and a G6PD-deficient one cannot. A 2024 review of the published cases found that every patient with documented G6PD deficiency who received high-dose vitamin C developed hemolysis. Two of the reported cases, both people with colorectal cancer given 1 g/kg, had haemoglobin fall below 50 g/L — severe enough to need blood transfusion — and both recovered once treated. The reviewing authors concluded that G6PD deficiency should be treated as a contraindication to high-dose vitamin C.
This is specifically about high-dose, typically intravenous vitamin C, not the 90 mg your body needs in a day or the amount in a standard supplement or a piece of fruit — ordinary intake has no such history. Anyone being offered high-dose vitamin C, especially by infusion, is the person this is actually relevant to, and it is a question for whoever is administering it, not a reason to avoid citrus.
Vitamin C (ascorbic acid) is a nutrient needed for collagen synthesis and immune function, found in citrus fruits and many vegetables. High-dose vitamin C given as an infusion is a separate safety concern from ordinary dietary vitamin C.
No — this concern is specific to high-dose, typically intravenous vitamin C, not ordinary dietary or standard supplement intake.
Every documented case in a 2024 review developed hemolysis; two needed a blood transfusion after haemoglobin fell below 50 g/L.
Anyone being offered it, especially by infusion — it is a question for whoever is administering it, not a reason to avoid citrus.
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Vitamin C (high-dose). MyGeneLog™. https://www.mygenelog.com/supplements/vitamin-c
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