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
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.
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
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
See Also: Potentially Toxic
Dosages and Side Effects of Nutrients