As a necessary part of the human diet, vitamins are often taken in supplement form in addition to food sources. As opposed to the water-soluble vitamins, A, D and E are fat-soluble, or stored in the body's fat cells, making them more prone to vitamin toxicity when taken in supplement form. Niacin, a water-soluble vitamin, is often taken in high doses to treat issues medical issues, making this another vitamin to watch for toxicity. Dosage amounts may vary depending on factors such as age, gender and weight. Always consult your physician before taking a supplement.
Vitamin A
Vitamin A is well known for helping the body maintain healthy vision. According to the National Institutes of Health's MedlinePlus, vitamin A toxicity may occur in adults who accumulate the supplement in their system by ingesting more than 25,000 international units per day. Too much vitamin A during pregnancy may also result in birth defects.
Vitamin D
Known as the sunshine vitamin, toxicity of this vitamin most often occurs with supplements and not with too much time spent in the sun. The National Institutes of Health's Office of Dietary Supplements recommends no more than 4,000 IU per day of vitamin D. Symptoms of toxicity may include fatigue, gastrointestinal upset, weakness and nausea.
Vitamin E
Vitamin E is recommended at a dosage of 1,100 IU per day for synthetic products and 1,500 IU per day for natural sources, notes the Office of Dietary Supplements. Vitamin E deficiency does not often show symptoms. Although it is an antioxidant with many benefits to the body, too much of this vitamin can increase the risk of stroke or inhibit the blood from properly clotting.
Niacin
Also known as vitamin B3, niacin is often used in megadoses to help treat conditions such as high cholesterol. Commonly known as the "niacin flush," a toxic dose of niacin may cause a burning feeling in the upper body and face, including tingling red skin. Other side effects of niacin toxicity involve liver damage, ulcers and reduced amounts of other B vitamins.
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