Vitamin and mineral supplements are widely used, particularly during illness or pregnancy. However the safety of some substances has come under fire, following the publication of an expert group report on dosage levels. But which supplements are affected and what does this mean for consumers? Vitamins come in two forms: water-soluble and fat-soluble. Water soluble vitamins cover both Vitamin C and eight vitamins labeled as derivatives of vitamin B while fat soluble vitamins include vitamins K, A, E and D.
Niacin (Vitamin B3)
Niacin taken in high doses is known to cause a wide range of adverse effects. The RDA for niacin is 20 milligrams. Niacin is marketed in dietary supplements at potencies of 250 mg, 400 mg, and 500 mg, in both immediate and slow-release formulations. Daily doses of 500 mg from slow-release formulations, and 750 mg of immediate-release niacin, have been associated with severe adverse reactions, including gastrointestinal distress (burning pain, nausea, vomiting, bloating, cramping, and diarrhea) and mild to severe liver damage.
Selenium
Selenium is a mineral found in dietary supplement products. At high doses (approximately 800 to 1,000 micrograms per day), selenium can cause tissue damage, especially in tissues or organs that concentrate the element. The toxicity of selenium depends upon the chemical form of selenium in the ingested supplement and upon the selenium levels in the foods consumed. Human injuries have occurred following ingestion of high doses over a few weeks.
Vitamin A
Vitamin A is found in several forms in dietary supplements. Preformed vitamin A (vitamin A acetate and vitamin A palmitate) has well-recognized toxicity when consumed at levels of 25,000 International Units (IU) per day, or higher. (Beta-carotene does not have the potential for adverse effects that the other forms of vitamin A do, because high intakes of beta-carotene are converted to vitamin A in the body at much lower levels). The RDA for vitamin A is 1,000 retinol equivalents (RE) for men, which is equivalent to 3,300 IU of preformed vitamin A, and 80 percent of these amounts for women.
Vitamin B6
Neurologic toxicity, including ataxia (alteration in balance) and sensory neuropathy (changes in sensations due to nerve injury), is associated with intake of vitamin B6 (pyridoxine) supplements at levels above 100 milligrams per day. As little as 50 milligrams per day has caused resumption of symptoms in an individual previously injured by higher intakes. The RDA for vitamin B6 is 2 milligrams. Vitamin B6 is marketed in capsules containing dosages in the 100-, 200-, and 500-milligrams range.
Although we have this constant urge of overdosing ourselves with vitamin supplements, it will be good to note that overdosage can create adverse effects.