Taking Too Much of a Supplement

There's increasing evidence that too much of some nutrients may be harmful. While most nutrients are safe, some can be dangerous and too much of anything can be toxic. The fat-soluble vitamins that can accumulate in the body, such as vitamins A and D, are particularly suspect. Please see the table for a listing of the known toxic levels of most nutrients and the symptoms and diseases that excessive supplementation may cause. The acute toxicity usually results from one or two large doses, while chronic toxicity usually refers to months of supplementation or excessive exposure in water or food. Unless otherwise noted, all the data in the table refer to chronic adult dosages. The nutrient with the greatest risk of toxicity is vitamin A, especially for children and pregnant women.

If you take supplements, your goal is to stay within the vitamin safety zone, that range beginning at the U.S. Recommended Daily Allowance (USRDA) and ending "at a level that is still safe and well below the toxicity level," says John Hathcock, Ph.D., a vitamin-toxicity expert with the U.S. Food and Drug Administration's (FDA) experimental nutritional section. It's not easy for a vitamin-consuming public to decide where to draw the line between safe and excessive micrograms, milligrams or international units. "There are no officially established limits for maximum doses. We've spent a lot of time debating and establishing the USRDAs at the low end, but no one's set suggested guidelines for the other end," says Dr. Hathcock.

Research has shown that many people either don't eat enough or do not eat balanced meals. Then there are people with medical conditions, pregnant women, the elderly and others who may have increased needs for specific nutrients. Which is why so many people turn to supplements. An FDA survey shows that about 40 percent of the general population take supplements daily, with women taking more than men. Among the elderly, surveys show that between 66 and 72 percent take supplements.

It's also estimated that 5 to 10 percent of the people who take supplements ingest megadoses, defined by some researchers as ten times the USRDA or more, of certain vitamins and minerals.

If you're wondering whether your personal vitamin program falls within safe bounds, the answer's not easily had. "There are no reference guides or tables you can check to see what levels of vitamins trigger harmful effects," says Paul Saltman, Ph.D., a professor of biology doing research in nutrition at the University of California at San Diego. "That's because the danger levels vary from person to person and depend on factors such as weight, health status, metabolism, diet, nutritional status, the form of the nutrient and how often you take it.

Under no circumstances should dosages near those noted as toxic be taken without the expert guidance of a physician skilled in nutritional medicine. While some people can take more of a nutrient than the toxic dosage and experience no ill effects, some can experience a toxic effect at even lower dosages. You are your own best advisor of your individual reactions to any supplement. Even at lower dosages, always monitor yourself carefully and respect the feedback your body provides.

Jane Brody, the New York Times Columnist and author of Jane Brody's Nutrition Book reported:

A 46-year-old actress had suffered for three years from weird, debilitating symptoms, including muscular weakness, weight loss, and severe abdominal pain. Her career was destroyed and she could barely walk before doctors realized she was suffering from lead poisoning as a result of taking bone meal, prescribed by her doctor for menstrual cramps. Her myth-driven effort to preserve her health by taking megadoses of calcium and other minerals in the form of bone meal had backfired completely. She hadn't known-and none of the twenty-two doctors she saw thought to ask-that bone meal could be hazardous. However, since bones help to protect the body from toxic substances like lead by removing them from the blood and storing them, bone meal can be a source of dangerous substances.

Many minerals themselves are toxic in large doses. For some, the body insists on a critical balance among them to function effectively. If this balance is disrupted by a megadose of one mineral, a relative shortage of another may be the result. For example, too much phosphorus increases the need for calcium and may produce a calcium deficiency even if you're consuming calcium in recommended amounts. Other minerals, such as iron and magnesium, can be stored in the body and may build up to produce toxic symptoms. And most of the so called trace minerals, which are needed in only micro quantities, are deadly poisons in doses much beyond the amounts essential for good nutritional health

See Also: Potentially Toxic Dosages and Side Effects of Nutrients