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Contraindications and Possible Adverse Effects of Therapeutic Diets and Supplements

By Vivekan Flint

It is now well established that good nutrition plays an important role in disease prevention. But controversy continues to swirl around the use of special diets and supplements as treatments for many existing medical conditions.

Proponents of the benefits of these nutritional therapies are fervent in their convictions. With equal passion, some members of the conventional medical community lump all nutritional and dietary therapies under the same rubric -- quackery. To patients who are seeking sound and reliable information about supplements and diets, this makes for a frustrating and befuddling situation.

The debate concerning the use of supplements is particularly intense because the use of individual nutrients for the treatment of disease is a recent development, and fairly little research has been carried out in this area. Many people mistakenly think vitamins and other nutritional supplements are safe because they are "natural". That may have been true once, when nutrients were consumed only in their natural form -- in food.

Today, technology allows us to consume megadoses of these nutrients. These large doses are taken out of context of the natural relationships with the thousands of other substances found in foods.

Some nutrients, such as vitamin A, are known to be toxic in high doses, and such risks are straightforward. What remains unknown is whether taking isolated substances at high doses might somehow disrupt the body's biochemical balance and cause long term problems or side effects.3 The question then becomes, is the benefit of taking high doses of supplements worth the possible risks?

Therapeutic diets are controversial too, less because of the risk of overdose than the possibility that severe restrictions can lead to deficiencies of various kinds. Most of the dietary approaches to illness have not been systematically studied in humans, and proof of their effectiveness has not been established. Clearly more research is needed to evaluate the value of these diets in human studies.

Recommended Daily Allowances

Most people are familiar with the Recommended Daily Allowances (RDA) for vitamins and minerals that have been established by the Food and Nutrition Board of the National Research Council. The RDA is defined as the level of intake of an essential nutrient that is judged to be adequate to meet the known needs of healthy people. At these levels, in other words, people should not develop the deficiency illness associated with a lack of that nutrient.3

The RDA does not apply to people with special nutritional needs, nor does it suggest that these are the optimal dietary levels for these nutrients for normal people. We now know that mild to moderate deficiency of basic nutrients, while not causing the classic deficiency illnesses, may contribute to a host of other illnesses1, especially in today's world, where stress and poor lifestyle habits may tax the body's nutritional resources. Scientific data suggest that the consumption of many nutrients above the RDAs may prevent or combat many common illnesses.3

When to Consult an Expert

When should you seek advice from a nutritional expert? Unfortunately, there are no hard and fast rules. But consider seeking help if you're planning to use a diet or supplements to treat a serious medical condition. Look for a practitioner who is adequately trained in the therapeutic use of supplements or diet. Most physicians are not trained this way, although increasing numbers of doctors are interested in the field. Always tell your physician when you begin to take supplements at levels above those found in a multi-vitamin, since they may interact with or affect the actions of other medications.

Nutritionists and dietitians are conventionally trained specialists in the role of nutrition in the prevention and treatment of disease. Most nutritionists and dietitians are found in institutional settings, but a growing number are operating consulting or independent practices. Dietitians were once considered conservative and narrowly focused, but this is rapidly changing as the profession gradually incorporates many nutritional concepts that were once considered far outside the mainstream.

Orthomolecular medicine is the field that specializes in the use of megadoses of vitamins to treat illness. Naturopaths also have extensive training in nutrition and use it as part of an overall approach to illness that de-emphasizes the use of drugs. Homeopaths, herbalists, chiropractors and acupuncturists also may also incorporate dietary advice into their treatments. Well-meaning and perhaps sound dietary advice may be offered by other practitioners ranging from massage therapists to yoga instructors. It is wise to be wary of advice from anyone who has not received formal training, or to implement such advice without doing some research of your own.

Beware of "true believers" who promote extreme diets or who claim one dietary approach will cure all illnesses. It is entirely possible that dietary approaches will be demonstrated to be the treatments of choice for some illnesses that mainstream medicine currently finds problematic; but it is wise to be cautious about claims that dietary therapies or nutritional supplements will vanquish an illness that is incurable by mainstream medicine. And do not rely solely on the results of unconventional diagnostic techniques such as hair analysis, applied kinesiology, or "intuitive" nutritional assessments.

Given the level of controversy concerning the appropriate use of diets and supplements, even among those trained in nutrition, a few guidelines will help ensure the safe use of these approaches:

Probably the greatest danger of self-prescribed diets and supplements is not adverse reactions or nutritional deficiencies, but failure to seek medical diagnosis and known effective treatments for an underlying condition.

More and more practitioners agree that multivitamin and mineral supplements can be useful because of the stress today's lifestyles can put on the body. But all agree that supplements do not substitute for a nutritious diet.

Be sure to research the possible adverse effects of any supplement you intend to use in doses higher than those recommended on the packaging. If you have any doubts, consult a practitioner trained in nutrition. Do not assume large doses of supplements are safe.

Any major dietary change, particularly one that involves elimination of entire food groups, should be carried in consultation with an expert in nutrition.

Special diets should be practiced in moderation. Rapid weight loss is cause for concern.

Cautions for Specific Nutrients

For purposes of comparison, the Recommended Daily Allowances for the essential nutrients are listed below. All these nutrients are necessary for human health, and ideally, they should be consumed in the diet. Most are found in multivitamin/mineral tablets at safe doses. People with deficiencies or specific health conditions may benefit from high doses of some of these substances when this use is monitored by a trained nutritional counselor.

Nutrient

RDA

Vitamin A

10,000 IU

Vitamin B1 (Thiamine)

1.5 mg

Vitamin B2 (Riboflavin)

1.7 mg

Vitamin B3 (Niacin)

20 mg

Vitamin B6 (Pyridoxine)

2 mg

Vitamin C

60 mg

Vitamin D

400 IU

Vitamin E

30 IU

Beta Carotene

15-50 mg

Folic Acid

0.2 mg

Calcium

1,200 mg

Iron

15 mg

Zinc

15 mg

Chromium

100 mg

Iodine

0.15 mg

(IU = international units; mg = milligrams)

Contraindications are circumstances in which specific supplements should not be taken. Contraindications for each nutrient are listed below, along with possible adverse reactions that may occur when supplements are taken at high doses. These adverse effects generally occur only at doses in excess of recommended levels -- not at the dosages typically found in ordinary multivitamin/mineral tablets. Special circumstances are also listed where specific supplements should be used only under medical supervision.

The full range of possible supplement/drug interactions is not well understood, and this list does not cover all possible contraindications or adverse effects.

Vitamin A

Contraindications

Women should not take vitamin A supplements during pregnancy. Dosages greater than 10,000 IU during pregnancy (specifically during the first 7 weeks after conception) have probably been the cause of 1 in 57 cases of birth defects in the United States. Women who may become pregnant should keep doses of vitamin A below 5,000 IU daily.5

Possible Adverse Effects

Vitamin A toxicity is by far the most widely reported problem arising from supplement overdoses. Even so, only 200 cases (unrelated to pregnancy) are thought to occur worldwide each year. How much vitamin A causes problems? The answer varies with the individual. Doses of 25,000-50,000 IU daily for several months can be toxic for people with liver problems2, for those taking certain drugs1, or for heavy drinkers. Generally, doses over 10,000 IU daily should be taken only under the supervision of a nutrition expert.3

Vitamin B6 (pyridoxine)

Contraindications

Diabetics should use B6 only under the supervision of a skilled practitioner, since it may affect blood sugar levels. Vitamin B6 may affect the actions of anticonvulsant medications, so epileptics should take it only under skilled supervison.3

Possible Adverse Effects

This is a controversial issue, but some people who take high doses of vitamin B6 over a long period of time may experience symptoms such as tingling, numbness, or weakness in the extremities due to nerve damage. But studies indicate that doses smaller than 500 mg per day appear to be safe.1 Doses greater than 50 mg should be spread over the course of the day.5

Vitamin C

Contraindications

Diabetics should take vitamin C supplements only under supervision, since it may affect blood sugar levels.3 People with genetic iron disorders should consult their physicians before using vitamin C supplements, since it increases the rate of iron absorbtion.1

Possible Adverse Effects

Vitamin C is generally regarded as one of the safest vitamins. Too much vitamin C can cause diarrhea.2

Based on early studies, there has been some concern that taking vitamin C might increase the risk of developing kidney stones. But more recent research have found no corroborating evidence of any link between vitamin C and kidney stones.1

Some researchers believe that abruptly ending high-dose vitamin C supplementation can cause "rebound scurvy" (the vitamin C deficiency disease). This is controversial, but it is probably wise to reduce high doses gradually.5

Folic Acid

Contraindications

Folic acid supplements may reduce the effectiveness of methotrexate (Rheumatrex), colchicine (Colbenemeid), trimethoprim (Trimpex, Bactrim, Septra), pyrimethamine (Daraprim, Fansidor), trimetrexate (Neutrexin) and phenytoin (Dilantin). If you're taking any of those drugs, consult your physician about using folic acid.4 High doses of folic acid may increase seizure activity in epileptics.5 Folic acid can mask symptoms of vitamin B12 deficiency (pernicious anemia).

Possible Adverse Effects

People at risk for pernicious anemia should use folic acid supplements only under medical supervision. Risk factors include a family history of the condition, as well as some autoimmune endocrine diseases such as type 1 diabetes, hypoparathyroidism, Addison's disease, hypopituitarism, testicular dysfunction, Graves disease, chronic thyroiditis, myasthenia gravis, secondary amenorrhea, vitiligo, and candidiasis.

Niacin

Contraindications

Diabetics should use niacin only under supervision, since it may affect blood sugar levels.3 Niacin should be avoided by people with liver disease, gout and peptic ulcers.5 Niacin may affect anticonvulsant medications taken by epileptics and should be used only under medical supervison.3

Possible Adverse Effects

Niacin supplementation may causes flushing, nausea, diarrhea, headache and fatigue.4 Niacin in high doses can be toxic to the liver and should be taken only under a physician's supervision. There have been reports that use of time-release niacin has resulted in severe, permanent liver damage.1

Tryptophan

Contraindications

Tryptophan should not be used by people with asthma. It is converted in the body to serotonin, which causes broncho-constriction in asthmatics.3

Possible Adverse Effects

Tryptophan was taken off the market in the United States in 1990 because of evidence that imported supplies contained a contaminant that caused a serious disorder in some users. This effect was not due to tryptophan itself, and its return to market is contingent upon measures that will insure the purity of the supplement.

Lysine

Contraindications

Lysine may raise levels of cholesterol in the blood. People with high cholesterol should have their levels monitored while taking lysine supplements.3

Calcium

Contraindications

People with hyperparathyroidism (overactive parathyroid gland) or hypercalcemia due to cancer should only take calcium under the supervision of a physician.5

Possible Adverse Effects

High doses of calcium can cause constipation4 and increase the risk of kidney stones and soft-tissue calcification.5

Chromium

Contraindications

Diabetics should use chromium only under medical supervision, since it affects blood sugar levels.3

Copper

Contraindications

Diabetics should use copper only under supervision, since it affects blood sugar levels affected.3

Possible Adverse Effects

It is unusual for anyone to be deficient in copper and to require supplements. It is probably safe to take 2-4 mg per day, but doses of 35 mg per day are toxic.4

Vitamin D

Possible Adverse Effects

Doses larger than 1,000 IU a day are not recommended. High consumption of vitamin D can raise the levels of calcium in the blood to dangerous levels and can result in calcium being deposited into internal organs.5

Vitamin K

Contraindications

People using anticoagulant drugs such as Warfarin or Coumadin should not take vitamin K.5

Iron

Possible Adverse Effects

Iron supplements are a leading cause of fatal poisonings in children. Adults should keep iron tablets in a locked cabinet out of reach of young children.

Iron deficiency is the most common nutrient deficiency in the United States. The groups at highest risk are infants under two years of age, teenage girls, pregnant women and the elderly. Extreme fatigue is a primary symptom of anemia, the last stage of iron deficiency. However, iron overload can result in heart disease, infection and possibly even cancer.5 Iron supplements, therefore, should only be used when tests show a deficiency exists.4

Magnesium

Contraindications

People with kidney disease or severe heart disease should not use magnesium supplements except under a physician's supervision.5

Possible Adverse Effects

Because healthy kidneys can excrete six grams of magnesium a day, it is difficult to overdose. But toxic levels can result from the abuse of magnesium-containing laxatives. The early signs of toxicity are nausea, vomiting and flushing.4 Even small doses of magnesium can cause diarrhea in some people.

Potassium

Contraindications

People with kidney disease or severe heart disease should not take potassium supplements except under a physician's supervision.5 People taking certain diuretic drugs may need potassium supplements, but those on heart medications should consult their physician first.

Possible Adverse Effects

Potassium (beyond levels found in vitamin/mineral tablets) should not be taken except under supervision. In high doses, potassium may cause abnormal heart rhythms and death.4

Zinc

Contraindications

People with high cholesterol should use zinc only under supervision, since high doses of zinc may elevate cholesterol levels in some cases.3

Possible Adverse Effects

High doses of zinc (100-300 mg daily) can impair immune system function. Taking too much zinc can also lead to severe copper deficiency.2

Manganese

Contraindications

Diabetics should use manganese only under supervision, since it may affect blood sugar levels.3

Selenium

Possible Adverse Effects

The human body needs only minute amounts of selenium. It may be toxic in amounts greater than 1000 mcg (micrograms) daily. Toxicity can cause hair loss, fatigue, brittle fingernails, muscle discomfort, nausea, poor appetite, weight loss, dermatitis, garlic breath odor, and suppression of immune system function.2

Iodine

Possible Adverse Effects

Iodine in the form of an antiseptic is poisonous if swallowed.3

Choline

Possible Adverse Effects

At high doses (20 grams) choline produces a "fishy" odor. Choline in the form of phosphatidylcholine should not be taken by people with depression unless under supervision, since it can worsen symptoms.5

Fiber

Contraindications

Fiber supplements in pill form should not be taken by people with esophageal disorders, since they may expand and cause an obstruction.5

Possible Adverse Effects

Increasing dietary fiber may cause gas and abdominal discomfort until the body adjusts. Fiber supplements may also interfere with the absorption of drugs, so it's best to separate the two by a couple of hours.5

Omega-6 Fatty Acids

Contraindications

People with temporal-lobe epilepsy should not use omega-6 fatty acids.3

Notes

1. Richard A. Passwater, Ph.D., "Vitamins, Immune Response and Safety: An Interview with Dr. Adrianne Bendich," Whole Foods Magazine. HealthWorld Online.

2. George Lewith, Julian Kenyon and Peter Lewis, Complementary Medicine: An Integrated Approach (Oxford: Oxford University Press, 1996), p. 108-9.

3. Melvyn Werbach, M.D., Healing Through Nutrition: A Natural Approach to Treating 50 Common Illnesses With Diet and Nutrients (New York: Harper Collins Publishers, 1993).

4. Adriane Fugh-Berman, M.D., Alternative Medicine: What Works (Tucson, AZ: Odonian Press, 1996).

5. Michael T. Murray, N.D., Encyclopedia of Nutritional Supplements (Rocklin, CA: Prima Publishing, 1996).

Copyright © 1998 WebMD, Inc. All rights reserved. WebMD Electronic Library Collection



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