Vitamin Toxicity Health Article

Definition

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.

Overview

Vitamins are organic molecules in food that are needed in small amounts for growth, reproduction, and the maintenance of good health. Some vitamins can be dissolved 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. The 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. However, megadoses with the fat-soluble vitamins are more likely to become toxic than with water-soluble vitamins because fat-soluble vitamins are often stored in the body while excess water-soluble vitamins are usually excreted in the urine. Vitamins A and D are the most likely to produce hypervitaminosis in large doses, while riboflavin, pantothenic acid, biotin, and vitamin C appear to be the least likely to cause problems.

Vitamins in medical treatment

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 such as neural tube defects, and possibly reduce the risk of cancer. Therapy for diseases brings with it the risk for irreversible vitamin toxicity only in the case of vitamin D. This vitamin is toxic at levels that are only moderately greater than the recommended dietary allowance (RDA). Niacin is commonly used as a drug for the treatment of heart disease, but niacin is far less toxic than vitamin D. Vitamin toxicity is not a risk with medically supervised therapy using any of the other vitamins.

Vitamin megadoses

With the exception of folic acid supplements, the practice of taking vitamin supplements 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 take vitamins at levels far greater than the RDA. These high levels are sometimes called vitamin megadoses. Megadoses are harmless for most vitamins. But in the cases of a few of the vitamins—specifically, vitamins D, A, and B₆—megadoses can be harmful or fatal. Researchers have also started to look more closely at megadoses of vitamins C and E, since indirect evidence suggests that these two vitamins may reduce the risks of cancer, heart disease, and aging. It is not yet clear whether taking megadoses of either vitamin C or vitamin E has any influence on health. 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 when combined with smoking.

Fat-soluble vitamins

VITAMIN D. Vitamins D and 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. The patient may experience constipation alternating with diarrhea, or have tingling sensations in the mouth. The toxic dose of vitamin D depends on its frequency. In infants, a single dose of 15 milligrams (mg) or greater may be toxic, but it is also the case that daily doses of 1.0 mg over a prolonged period may be toxic. In adults, a daily dose of 1.0 to 2.0 mg of vitamin D is toxic when consumed for a prolonged period. A single dose of about 50 mg or greater is toxic for adults. The immediate effect of an overdose of vitamin D is abdominal cramps, nausea, and vomiting. Toxic doses of vitamin D taken over a prolonged period of time can result in irreversible deposits of calcium crystals in the soft tissues of the body that may damage the heart, lungs, and kidneys. The dietary reference intake (DRI) suggests an upper tolerable limit of 25 micrograms (mcg) per day for children and 50 mcg per day for adults. The DRI is between 5–15 mcg from childhood to adulthood in the absence of adequate sunlight. Older adults have a requirement on the higher end of the scale due to generally reduced sun exposure.

VITAMIN A. 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 of water in the brain (hydrocephalus), vomiting, tiredness, constipation, bone pain, and severe headaches. The skin may acquire a rough and dry appearance, with hair loss and brittle nails. Vitamin A toxicity is a special issue during pregnancy. Expectant mothers who take 10 mg vitamin A or more on a daily basis may have an infant with birth defects. These birth defects include abnormalities of the face, nervous system, heart, and thymus gland. It is possible to take in toxic levels of vitamin A by eating large quantities of certain foods. For example, about 30 grams of beef liver, 500 grams of eggs, or 2,500 grams of mackerel would supply 10 mg of retinol.

VITAMIN E. 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. The term absorption means the transfer of the vitamin from the gut into the bloodstream. Thus, large doses of vitamin E consumed over many weeks or months might result in deficiencies of vitamin D, vitamin A, and vitamin K. The DRI suggests an upper tolerable limit between 200–800 mg per day for children and teenagers, depending on age (younger children have requirements on the lower end of the scale), and 1000 mg per day for adults. The DRI is 15 mg per day for adults and pregnant women.

VITAMIN K. Prolonged consumption of megadoses of vitamin K (menadione) results in anemia, which is a reduced level of red blood cells in the bloodstream. When large doses 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. A daily injection of 10 mg of menadione into an infant for three days can kill the child. This tragic fact was discovered during the early days of vitamin research, when newborn infants were injected with menadione to prevent a disease known as hemorrhagic disease of the newborn. Today, a different form of vitamin K is used to protect infants against this disease.