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Vitamin Toxicity

Below we have addressed each vitamin in terms of its toxicity and known side effects. Some warnings are also given.

Vitamin A

Questions have been raised concerning the toxicity of vitamin A, which is known to be concentrated in the liver. Symptoms of vitamin A excess include: hair loss, headaches, dizziness and blurred vision, gastrointestinal disturbances (such as nausea and diarrhea), skin inflammation and itchiness, and poor muscular coordination and possibly reduced bone mineral density.

Toxic symptoms can also arise after consuming very large amounts of vitamin A over a short period of time.

Beta-carotene does not cause toxicity.

Pregnant women and those planning pregnancy should not take in excess of 7,500 IU of vitamin A per day because of the risk of birth defects. You should also avoid eating animal livers because of the high concentration of vitamin A in livers.

Vitamin B1

Vitamin B1 toxicity is very rare and this is one of the safest of the vitamins. However, excessive vitamin B1 can deplete other B vitamins and disrupt insulin and thyroid production.

Vitamin B2

You may notice a yellow coloration of the urine when you take supplements of vitamin B2. This is completely normal.

Vitamin B3

Those suffering from diabetes, glaucoma, gout, liver disease, or peptic ulcers should use niacin supplements cautiously. Consuming over 500 mg per day for an extended length of time may result in liver damage.

High doses of nicotinic acid and nicotinamide can alter liver function tests, changes which quickly reverse when treatment is stopped or the dosage reduced.

Niacin can cause a somewhat irritating but harmless flushing when first taking a dose of 50 milligrams or more. A no-flush variety, inositol hexanicotinate is the only form of time release niacin that is recommended; other forms of time-release niacin are a liver irritant and should not be consumed. The niacin flush may be worse when also taking antibiotics.

Some studies indicate that doses higher than 500 mg may cause some liver damage.

Vitamin B5

This is one of the safest vitamins. It has no known side effects or toxic levels.

Vitamin B6

Vitamin B6 should not be taken by anyone undergoing levodopa treatment for Parkinson's disease.

Excess vitamin B6 can deplete other B vitamins, so always take it in balanced amounts. Therapeutic dosages should not be used long-term unless they are under a total of 100 - 200 mg daily (except with the supervision of a physician).

If taking doses larger than 50 mg for therapeutic benefit, the doses should be divided into 50 mg doses, which can be taken during the course of the day. This is important because the liver is unable to handle more than a 50 mg dose at a time.

Vitamin B12

There are no reported cases of vitamin B12 toxicity and it appears to be safe at any dosage level.

Folic Acid

High doses of folic acid (5-10mg) may cause gas, poor appetite, and stomach upset. Those with epilepsy should avoid folic acid in high doses, because it may result in increased occurrence of seizures.

If taking pancreatic enzymes, which may reduce folic acid absorption, take the two supplements four to six hours apart.

Vitamin C

Vitamin C can alter the results of blood and urine testing, including these for diabetes. (Before any tests, let your physician know if you are taking vitamin C supplements.)

Mega doses of vitamin C should be avoided in individuals with a history of renal stones due to oxalate formation or hemochromatosis or other diseases related to excessive iron accumulation.

Extremely high dosage of vitamin C may predispose premature infants to hemolytic anemia due to the fragility of their red blood cells.

Be careful of taking aspirin and vitamin C together. Vitamin C may cause stomach irritation.

Vitamin E

Vitamin E appears to be safe when consumed in amounts up to 1,000 IU a day, although diarrhea and headaches have been reported in some people. Doses of over 800 IU a day of vitamin E may interfere with the body's ability to clot blood, posing a risk to people taking blood thinners (anticoagulants). In addition, high doses of vitamin E may inhibit the absorption of vitamin A.

Vitamin D

Vitamin D is fat soluble and large or repeated doses can build up to toxic levels in the body. The symptoms and signs of toxicity include: nausea and vomiting, calcium deposits, unusual thirst, sore eyes, itching skin, kidney damage, damage to the arteries, irregular heart beat, and high blood pressure.

Vitamin K

It is not recommended that you take more that 500mcg of synthetic vitamin K (mendadione). High to toxic uptake of the synthetic form can cause flushing and sweating, jaundice and anemia.

If you are taking anti-coagulant medication (to prevent blood clotting), consult your medical practitioner before taking Vitamin K supplement.


There are no known toxic effects of biotin.


Choline should always be taken with B group vitamins and preferably with a meal containing protein. Evidence suggests an upper tolerable limit of Choline in adults of 3.5 grams per day. Significantly exceeding this dose should be avoided.


There are no known toxic effects of inositol.

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Bland, J. 1996, Contemporary Nutrition. J & B Associates.

Davies, S. and A. Stewart., 1997, Nutritional Medicine. Pan.

Holden, S., Hudson, K., Tilman, J. & D. Wolf, 2003, The Ultimate Guide to Health from Nature. Asrolog Publication.

Pressman, A. and S. Buff, 2000, The Complete Idiot's Guide to Vitamins and Minerals. (2nd Ed.) Alpha Books.

Soothill, R. 1996, The Choice Guide to Vitamins and Minerals. A Choice Book Publication.

Sullivan, K. 2002, Vitamins and Minerals: A Practical Approach to a Health Diet and Safe Supplementation. Harper Collins.

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Taking supplements is generally a very safe thing to do. After reading this page you will be a better informed and safer consumer.


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