Vitamins That Are Toxic In Large Quantities

Although necessary for human health, certain vitamins can become toxic to you if you take too much of them. This usually happens when a supplement you're taking contains an excessive amount of a certain vitamin, or you misinterpret the way you're supposed to take it. It's best to check with your doctor before you start taking a vitamin supplement to make sure the dose is appropriate.

Vitamin A

Vitamin A is a fat-soluble vitamin that is well known for its ability to protect the eyes from damage. The U.S. Food and Drug Administration recommends that the average adult take in 5,000 I.U. of vitamin A a day through a combination of diet and supplementation. Going over the recommended amount can cause both immediate and long-term toxicity. Toxicity has been seen at daily doses as low as 10,000 I.U., according to a review published in the August 1990 issue of "The American Journal of Clinical Nutrition." Certain conditions, such as the use of alcohol or a low protein diet, can make toxicity worse. Symptoms of a vitamin A overdose include general weakness and tiredness, intracranial hypertension and liver problems, including cirrhosis.

Vitamin D

Vitamin D is the vitamin responsible for helping the body absorb calcium. The recommended daily amount of calcium is 600 I.U. a day for children and adults up to age 70, according to the Institute of Medicine. Adults over 70 should take in 800 I.U. daily. The biggest concern with taking too much vitamin D is the development of hypercalcemia, too much calcium in the blood. The excess calcium causes symptoms such as nausea and vomiting, loss of appetite, constipation, general weakness and confusion. In severe cases, calcium can build up in your heart and kidneys and cause serious damage.

Vitamin E

Vitamin E is a vitamin known for its antioxidant effects. The Food and Nutrition Board of the National Academy of Sciences recommends you take in 15 I.U. of vitamin E a day. The tolerable upper intake level -- the amount most people can take without developing toxic effects -- is 1,100 I.U. per day for natural vitamin E and 1,500 I.U. a day for synthetic vitamin E. The most dangerous effect of taking too much vitamin E is abnormal bleeding. Vitamin E can stop vitamin K from working. Vitamin K is needed to maintain proper blood clotting. High doses of vitamin E are particularly dangerous in people who are already deficient in vitamin K and in those with iron-deficiency anemia. Long-term toxicity may cause congestive heart failure and make you more prone to infection.

Other Vitamins

Most vitamins that can cause toxicity are fat-soluble. Some water-soluble vitamins, like vitamin B-6 , can cause problems as well. It can cause peripheral sensory neuropathy and nerve degeneration if you take it consistently in ultra-high doses, according to a review published in the January 2010 issue of "Molecules." Excessive amounts of vitamin C, while not technically considered toxic, can have a severe laxative effect. It's best to consult a physician before starting supplementation with any kind of vitamin to avoid possibly dangerous side effects.