What Vitamin Is Bad for G6PD? Understanding Risks and Safe Alternatives

November 16, 2025 •

5 min read

Over 329 million people worldwide have G6PD deficiency, and for this population, certain vitamins can be dangerous when taken in high doses. The primary vitamin that is bad for G6PD patients at high concentrations is vitamin C, though synthetic forms of vitamin K also pose a significant risk of triggering hemolytic anemia.

Quick Summary

For individuals with G6PD deficiency, high doses of vitamin C and synthetic vitamin K3 can act as oxidative agents, potentially causing dangerous red blood cell damage and hemolytic anemia.

Key Points

High-Dose Vitamin C: Intravenous or supraphysiologic doses of vitamin C (ascorbic acid) are dangerous for G6PD-deficient individuals, as they can trigger hemolytic anemia by acting as a pro-oxidant.
Synthetic Vitamin K3 (Menadione): The synthetic version of vitamin K, K3, is toxic and known to cause hemolysis; it should be completely avoided by those with G6PD deficiency.
Natural Vitamin K is Safe: The natural forms of vitamin K (K1 and K2), found in foods and supplements, do not pose the same hemolytic risk as the synthetic K3.
Folic Acid and Vitamin E are Generally Safe: Folic acid helps support new red blood cell production, while vitamin E acts as a protective antioxidant for G6PD-deficient red cells.
Dietary vs. Supplemental Risks: The primary risk from vitamin C comes from high-dose supplements or injections, not from consuming vitamin C-rich foods as part of a normal diet.
Consult a Professional: Due to the variability of G6PD deficiency, always consult a healthcare provider before taking any new supplement to ensure safety.

Understanding G6PD Deficiency and Oxidative Stress

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited genetic condition that affects red blood cells (RBCs). This enzyme is crucial for producing NADPH, a molecule that protects red blood cells from damage caused by oxidative stress. When an individual with this deficiency is exposed to certain triggers, such as particular foods or medications, their red blood cells can be damaged, leading to a condition called hemolytic anemia. Hemolytic anemia involves the premature breakdown of red blood cells, which can cause symptoms like fatigue, jaundice, and dark urine. Many common substances, including vitamins in high doses, can act as these oxidative triggers.

The Dangers of High-Dose Vitamin C (Ascorbic Acid)

While low to moderate doses of vitamin C are generally considered safe, high or “supraphysiologic” doses are a significant concern for G6PD-deficient individuals. Vitamin C is an antioxidant at normal levels, but at very high concentrations, it can paradoxically become a pro-oxidant.

Mechanism of Harm: At high doses, vitamin C can promote the production of hydrogen peroxide, a potent oxidant. For someone with G6PD deficiency, their red blood cells lack the necessary protective mechanisms (NADPH and glutathione) to neutralize this increased oxidative stress. The resulting damage can lead to rapid and severe intravascular hemolysis.
Case Study Examples: Several case reports document this risk. One report describes a patient receiving 80 grams of intravenous vitamin C for burns, which led to severe hemolysis and acute renal failure. Another case involved a G6PD-deficient male with HIV who experienced acute hemolysis after receiving 80 grams of intravenous vitamin C.
Sources of High-Dose Vitamin C: The risk comes from high-dose supplements, often administered intravenously in alternative or complementary therapies. It's not typically a concern for normal dietary intake of vitamin C.

Synthetic Vitamin K (Menadione) is a Major Risk

Different forms of vitamin K exist, and it is crucial to distinguish between them for G6PD-deficient individuals. The synthetic form, vitamin K3 (menadione), is explicitly known to be harmful.

Toxic Form: Synthetic vitamin K3 (menadione) and its water-soluble derivatives are known to cause hemolysis and hyperbilirubinemia, especially in newborns with G6PD deficiency. For this reason, synthetic vitamin K3 is no longer approved for human use by the FDA in the United States.
Safe Forms: The naturally occurring forms, vitamin K1 (phylloquinone) and vitamin K2 (menaquinone), are considered safe. Vitamin K1 is often administered to newborns to prevent bleeding and has not been shown to increase oxidative damage in G6PD-deficient red blood cells.
The Controversy: While some older medical textbooks cautioned against all forms of vitamin K, modern evidence and the widespread use of vitamin K1 in newborns without widespread complications have largely dispelled these fears regarding the natural forms. The risk is specifically linked to the toxic synthetic analogue.

Safe and Potentially Beneficial Vitamins for G6PD

Not all vitamins are dangerous for those with G6PD deficiency. Some are considered safe and even beneficial for managing the condition and its effects.

Folic Acid: For patients with chronic hemolysis, which is the constant destruction of red blood cells, daily folic acid supplements are often recommended. Folic acid is vital for the production of new red blood cells, which helps the body keep up with the increased rate of destruction.
Vitamin E: As a powerful antioxidant, vitamin E has shown potential benefits in some studies for G6PD-deficient patients. It can help protect red blood cells from oxidative damage, and high-quality evidence suggests it can improve red blood cell parameters and reduce hemolysis. Several studies have found no adverse effects with daily oral supplementation.

Dietary vs. Supplemental Vitamins

It's important to differentiate between getting vitamins from food and taking high-dose supplements. For a G6PD-deficient individual, a balanced diet rich in vitamins and antioxidants from whole foods is the safest approach. Concerns about vitamin C arise primarily from high-dose, intravenous, or pharmacological administrations, not from eating vitamin C-rich fruits.

Comparison Table: Vitamin Risks for G6PD Deficiency


Vitamin Type	Risk to G6PD Individuals	Recommended for G6PD?
High-Dose Vitamin C	High risk. Acts as a pro-oxidant, causing hemolytic anemia.	No. High-dose supplements and infusions should be avoided.
Synthetic Vitamin K3	High risk. A toxic analogue that causes hemolysis.	No. Explicitly banned for human use in the US.
Natural Vitamin K1/K2	Safe. Not shown to increase oxidative damage at normal doses.	Yes. Generally considered safe for individuals with G6PD.
Vitamin E	Safe and potentially beneficial. Antioxidant effects may help reduce hemolysis.	Yes. Oral supplementation up to 800 IU daily appears safe.
Folic Acid	Safe and often beneficial. Helps in producing new red blood cells during chronic hemolysis.	Yes. Often prescribed for those experiencing chronic red cell destruction.

Conclusion

For individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency, knowing which vitamins to avoid is critical for preventing a potentially serious hemolytic crisis. High-dose vitamin C, particularly from intravenous infusions, poses a significant risk due to its pro-oxidant properties. Furthermore, the synthetic form of vitamin K, known as menadione (K3), is toxic and should be completely avoided. Natural forms of vitamin K (K1 and K2), as well as supplements like vitamin E and folic acid, are generally considered safe and may even be beneficial for managing the condition. Always consult with a healthcare provider before taking any supplements to ensure a safe and effective treatment plan tailored to your specific needs.

Safe Supplementation Practices

Always Consult a Physician: Before starting any new supplement, inform your doctor about your G6PD deficiency to assess for potential risks.
Opt for Whole Foods: Prioritize a balanced diet rich in vitamins from natural food sources instead of relying on supplements, especially for vitamin C.
Avoid High Doses: Steer clear of high-dose or megadose supplements, particularly for vitamin C.
Read Labels Carefully: Be vigilant about supplement ingredients. For vitamin K, ensure you are taking natural forms (K1 or K2) and not the synthetic menadione (K3).
Consider Safe Supplements: If prescribed by a doctor, supplements like folic acid and vitamin E can be helpful for managing certain aspects of G6PD deficiency.

Frequently Asked Questions

Yes, it is generally safe for individuals with G6PD deficiency to consume fruits and vegetables high in vitamin C. The risk arises from high-dose, concentrated supplements or intravenous infusions, not from the vitamin C obtained through a normal, balanced diet.

Synthetic vitamin K3, or menadione, is known to produce hemolysis (the destruction of red blood cells) in individuals with G6PD deficiency and is therefore contraindicated. Natural forms of the vitamin, K1 and K2, are not associated with this risk.

High doses of vitamin C can act as a pro-oxidant, generating harmful hydrogen peroxide that damages red blood cells. Since G6PD-deficient red blood cells lack the protective mechanisms to neutralize this oxidative stress, severe hemolytic anemia can occur.

Safety depends on the specific formulation. Individuals should read labels carefully to ensure multivitamins do not contain high doses of vitamin C or synthetic vitamin K3. Consulting a doctor before taking any multivitamin is the safest approach.

Yes, vitamin E is generally considered safe and potentially beneficial for those with G6PD deficiency. As an antioxidant, it can help protect red blood cells from oxidative damage, and studies have not reported adverse effects with oral supplementation up to 800 IU daily.

Extreme caution must be exercised with high-dose vitamin C in G6PD patients, even for conditions where it is being investigated as a therapy, such as sepsis. The risk of triggering severe hemolysis often outweighs the potential benefits.

Besides specific vitamins, other substances to avoid include fava beans, certain antimalarial drugs like primaquine, mothballs containing naphthalene, and some herbal supplements like henna. A physician can provide a comprehensive list.