How Much of Each Vitamin Can I Take Without Experiencing Negative Side Effects?

When it comes to giving medicine, the old saying used to be: "Two pills for a horse, one for a man." Among some consumers, that aphorism has been expanded so that, when taking vitamins, "the more the better." Not only does recent evidence conclusively prove this theory false, but there is strong Indication that so-called mega dose vitamin therapy can be dangerous- Vitamin A, in therapeutic quantities (500 to 1,000 retinol equivalents), is necessary to prevent night blindness and to maintain normal growth of tissues. Doses that exceed the recommended daily allowance (RDA) can produce headaches, nausea, vomiting, skin shedding, hair loss, fatigue, hemorrhage, disorientation, liver enlargement and bone pain.

Niacin is essential for energy metabolism. The RDA is 13 to 19 niacin equivalents. Overdose can cause skin flushing, heart-rhythm disturbances, headache, cramps, vomiting, diarrhea, elevated blood sugar, peptic ulcer and gout. Vitamin B6 is required for amino-acid metabolism and the formation of red blood cells. The RDA is about 2 mg. Excessive ingestion of pyridoxine produces nerve damage in legs and arms, seizures and peptic disease. B6 decreases the effect of the medicine L DOPA, so the vitamin is contraindicated in patients being treated with this drug for Parkinson's disease.

Vitamin Bl2 is probably the safest vitamin. The RDA is 2 micrograms, but no adverse effects are seen with much higher doses. Bl2 prevents pernicious anemia. But in cancer patients taking methotrexate, adverse interaction with B12 can occur. Vitamin C, with an RDA of 60 mg., plays a role in maintaining body tissues, including white blood cells. No responsible investigations have shown that high doses protect against the common cold or any other infection. In fact, massive doses may cause B12 deficiency, iron overload, diarrhea, kidney stones and breakdown of red blood cells. Ascorbic acid interferes with a. variety of laboratory tests and can interact with anticoagulant drugs. Rebound scurvy has been reported in women who suddenly stopped taking mega doses.

Vitamin D is necessary for healthy bones. The RDA is 200 to 400 international units. Chronic overdose can produce nausea, vomiting, diarrhea, headache, weight loss, weakness, fatigue, confusion, kidney failure, calcium deposits in kidneys, bone pain, cramps, excessive blood calcium and increased risk of heart attacks- Vitamin E is an antioxidant. Its precise role in the body is not completely understood- The RDA is 8 to 10 international units. The vitamin is useful in treating visual loss in certain premature infants and may be helpful in reducing painful breast lumpiness in women. Excessive doses have been reported to cause weakness, blood clots, high blood pressure, elevated blood sugar, nausea and fatigue. The vitamin enhances the effects of anticoagulants.

Source: Reavley, Nicola The New Encyclopedia of Vitamins, Minerals, Supplements, and Herbs: How They Are Best Used to Promote Health and Well Being 1999