A study published in the March 2000 issue of the "Archives of Family Medicine" reported that approximately 40 percent of 11,000 people questioned for the "Third National Health and Nutrition Examination Survey" reported taking a vitamin or mineral supplement in the previous month. While vitamin supplements may have health benefits, especially for those with low dietary vitamin intake, it's important to know that some vitamin supplements can be toxic in large doses.
Function
People take supplemental vitamins to fill perceived or real vitamin deficiencies caused either by inadequate dietary vitamin intake or reduced metabolic vitamin absorption. While clinical vitamin deficiencies are relatively rare in the Western world, those most at risk for vitamin deficiencies include the elderly, strict vegetarians and vegans, alcoholics with poor nutrition and individuals with malabsorption disorders.
Types
There are two basic types of vitamins: water-soluble and fat-soluble. Fat-soluble vitamins require the presence of lipids in the digestive system for absorption, while water-soluble vitamins don't. The body stores excess amounts of fat-soluble vitamins in the liver and fatty tissues, but excretes excesses of most water-soluble vitamins. Vitamin B-12 is the only water-soluble vitamin that is stored in the liver for later use, according to MayoClinic.com. Because the body excretes water-soluble vitamins, they rarely build up to toxic levels, but over-consumption of fat-soluble vitamins can quickly lead to toxicity.
Time Frame
Chronic hypervitaminosis, or vitamin toxicity, occurs due to vitamin buildup from over-supplementation over a significant period of time, but a single very large dose of some vitamins can cause acute hypervitaminosis.
Effects
Symptoms of vitamin A toxicity include stunted growth, liver and spleen abnormalities, hair loss, bone pain and increased inter-cranial pressure. Toxic levels of vitamin D can cause mental and physical retardation, reduction in bone density and kidney damage. Excessive consumption of vitamins E and K is not associated with hypervitaminosis, but taking too much vitamin E can cause nausea and abdominal upset.
Niacin is the only water-soluble vitamin associated with toxicity. It can cause abnormal liver function, abdominal cramps and irritability. While other water-soluble vitamins don't cause hypervitaminosis, consuming excessive amounts can cause uncomfortable intestinal symptoms.
Prevention
To prevent hypervitaminosis due to over-supplementation, consult your physician before beginning supplementation; always inform your physician of any supplements you're already taking; and consult your physician immediately if you experience any symptoms of hypervitaminosis.
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