Vitamin toxicity is a condition in which a person develops symptoms as side effects from taking massive doses of vitamins. Vitamins vary in the amounts that are required to cause toxicity and in the specific symptoms that result. Vitamin toxicity, which is also called hypervitaminosis or vitamin poisoning,is becoming more common in developed countries because of the popularity of vitamin supplements. Many people treat themselves for minor illnesses with large doses (megadoses) of vitamins.
Vitamins are organic molecules in food that are needed in small amounts for growth, reproduction, and the maintenance of good health. Some vitamins can bedissolved in oil or melted fat. These fat-soluble vitamins include vitamin D, vitamin E, vitamin A (retinol), and vitamin K. Other vitamins can be dissolved in water. These water-soluble vitamins include folate (folic acid), vitamin B12, biotin, vitamin B6, niacin, thiamin, riboflavin, pantothenic acid, and vitamin C (ascorbic acid). Taking too much of any vitamin can produce a toxic effect. Vitamin A and vitamin D are the most likelyto produce hypervitaminosis in large doses, while riboflavin, pantothenic acid, biotin, and vitamin C appear to be the least likely to cause problems.
Vitamin supplements are used for the treatment of various diseases or for reducing the risk of certain diseases. For example, moderate supplements of folic acid appear to reduce the risk for certain birth defects (neural tube defects), and possibly reduce the risk of cancer. Therapy for diseases brings withit the risk for irreversible vitamin toxicity only in the case of vitamin D.
With the exception of folic acid supplements, the practice of taking vitaminsupplements by healthy individuals has little or no relation to good health.Most adults in the United States can obtain enough vitamins by eating a well-balanced diet. It has, however, become increasingly common for people to takevitamins at levels far greater than the RDA. These high levels are sometimescalled vitamin megadoses. Megadoses are harmless for most vitamins. But in the cases of a few of the vitamins-- specifically vitamin D, vitamin A, and vitamin B6-- megadoses can be harmful or fatal. Some experts think that megadoses of vitamin C may protect people from cancer. On the other hand,other researchers have gathered indirect evidence that vitamin C megadoses may cause cancer.
Vitamin D and vitamin A are the most toxic of the fat-soluble vitamins. The symptoms of vitamin D toxicity are nausea, vomiting, pain in the joints, and loss of appetite. Toxic doses of vitamin D taken over a prolonged period of time result in irreversible deposits of calcium crystals in the soft tissues ofthe body that may damage the heart, lungs, and kidneys.
Vitamin A toxicity can occur with long-term consumption of 20 mg of retinol or more per day. The symptoms of vitamin A overdosing include accumulation ofwater in the brain (hydrocephalus), vomiting, tiredness, constipation, bone pain, and severe headaches.
Megadoses of vitamin E may produce headaches, tiredness, double vision, and diarrhea in humans. Studies with animals fed large doses of vitamin E have revealed that this vitamin may interfere with the absorption of other fat-soluble vitamins.
Prolonged consumption of megadoses of vitamin K (menadione) results in anemia, which is a reduced level of red blood cells in the bloodstream. When largedoses of menadione are given to infants, they result in the deposit of pigments in the brain, nerve damage, the destruction of red blood cells (hemolysis), and death.
Folate occurs in various forms in food. There are over a dozen related formsof folate. The folate in oral vitamin supplements occurs in only one form, however-- folic acid. Large doses of folic acid (20 grams/day) can result in eventual kidney damage.
Vitamin B12 is important in the treatment of pernicious anemia. Pernicious anemia is more common among middle-aged and older adults; it is usually detected in patients between the ages of 40 and 80. Although vitamin B12 toxicity is not an issue for patients being treated for perniciousanemia, treatment of these patients with folic acid may cause problems. Specifically, pernicious anemia is often first detected because the patient feelsweak or tired. If the anemia is not treated, the patient may suffer irreversible nerve damage. The problem with folic acid supplements is that the folicacid treatment prevents the anemia from developing, but allows the eventual nerve damage to occur.
Vitamin B6 is clearly toxic at doses about 1000 times the RDA. When the patient stops taking high doses of this vitamin, recovery begins aftertwo months. Complete recovery may take two to three years.
Large doses of vitamin C are considered to be toxic in persons with a familyhistory of or tendency to form kidney stones or gallbladder stones.
Niacin comes in two forms, nicotinic acid and nicotinamide. Either form can satisfy the adult requirement for this vitamin. Nicotinic acid, however, is toxic at levels of 100 times the RDA. It can cause flushing of the skin, nausea, diarrhea, and liver damage.
In all cases, treatment of vitamin toxicity requires discontinuing vitamin supplements. Vitamin D toxicity needs additional action to reduce the calcium levels in the bloodstream because it can cause abnormally high levels of plasma calcium (hypercalcemia). Severe hypercalcemia is a medical emergency and may be treated by infusing a solution of 0.9% sodium chloride into the patient's bloodstream. The infusion consists of two to three liters of salt water given over a period of one to two days.
The prognosis for reversing vitamin toxicity is excellent for most patients.Side effects usually go away as soon as overdoses are stopped. The exceptionsare severe vitamin D toxicity, severe vitamin A toxicity, and severe vitaminB6 toxicity. Too much vitamin D leads to deposits of calcium salts in the soft tissue of the body, which cannot be reversed. Birth defects dueto vitamin A toxicity cannot be reversed. Damage to the nervous system caused by megadoses of vitamin B6 can be reversed, but complete reversal may require a recovery period of over a year.