An Overview of Vitamin C Safety
Normal intakes of
vitamin C are probably safe for most people. However, high doses can cause problems, especially in people with certain medical conditions. You should talk with your healthcare provider prior to taking vitamin C if you have:
- Cancer (or a history of cancer)
- Diabetes
- Glucose 6-phosphate dehydrogenase deficiency
- Certain problems related to iron, including iron overload, hemochromatosis, thalassemia, or sideroblastic anemia
- Kidney stones
- Sickle cell disease
- Any allergies, including allergies to foods, dyes, or preservatives.
Also, let your healthcare provider know if you are:
- Pregnant or thinking of becoming pregnant
- Breastfeeding.
You should also be sure to tell your healthcare provider about all other medicines you are taking, including prescription and non-prescription medicines, vitamins, and herbal supplements.
Specific Vitamin C Safety Warnings and Precautions
Warnings and precautions to be aware of concerning the safety of vitamin C include the following:
- There is some concern that vitamin C supplementation could make chemotherapy for cancer less effective or could increase the growth of cancer cells. However, this is a controversial issue, and many researchers and healthcare providers do not think that vitamin C really causes such problems. Until more information is available, you should check with your healthcare provider before taking vitamin C (especially at high doses) if you have cancer or a history of cancer.
- Some studies have shown that vitamin C could increase blood sugar in people with diabetes, and one study showed that postmenopausal women with diabetes who took vitamin C had a higher risk of heart-related deaths. Until more information is available, it is a good idea check with your healthcare provider before taking vitamin C (especially at high doses) if you have diabetes.
- High doses of vitamin C can cause hemolysis (destruction of red blood cells) in people with glucose 6-phosphate dehydrogenase deficiency.
- Vitamin C increases the absorption of iron into the body. While this may be a beneficial effect for many people, it can be quite dangerous for some. In particular, it can cause problems for people with iron overload, hemochromatosis, thalassemia, or sideroblastic anemia.
- Vitamin C increases the risk of oxalate kidney stones (the most common type of kidney stones). If you have a history of this type of kidney stones, it is probably a good idea to avoid high-dose vitamin C supplementation.
- Vitamin C is acidic and can decrease the pH of blood. This can rarely cause a sickle cell crisis in people with sickle cell disease.
- Chewable vitamin C tablets have been known to cause erosion of the teeth. As unappetizing as it may seem (since the citrus flavor of vitamin C tablets and mint toothpaste are an unpleasant combination), it is a good idea to brush your teeth after chewing vitamin C tablets.
- Vitamin C can interact with some medications (see Vitamin C Drug Interactions for more information).
- Normal intakes of vitamin C are safe for pregnant or breastfeeding women. It is not known if higher doses are also safe (see Vitamin C and Pregnancy and Vitamin C and Breastfeeding).
