Dear Dr. Rona:
I am considering purchasing a multiple vitamin and mineral supplement containing 40 mg of zinc per capsule. The RDA is 15 mg, whereas this product supplies 40 mg/day. A couple of sources* I have read urge caution that going over the daily allowance may lead to a depressed immune system, poor wound healing, problems with taste and smell, skin problems, and lower healthy (HDL) cholesterol levels. The latter may lead to arterial aging, which seems to counter the "anti-aging" claim made in supplement advertisements.
I would be very interested in understanding why this supplement uses such a high level of zinc and be reassured that it is not a health risk.
* The RealAge Diet (2001: Roizen, MD), and Eat, Drink, and Be Healthy (2001: Willett, MD)
MJ
Dear MJ:
According to the latest pronouncements made by the reputable Food and Nutrition Board, zinc, when used orally, is safe in amounts that do not exceed the tolerable upper intake level (UL) of 40 mg per day. The RDA of 15 mg daily is only enough to prevent deficiency in the average adult and does not take other factors into consideration, such as stress, pollution, diet quality and activity level. One can make many arguments for an intake of 40 mg per day in adults for optimal health. The 15 mg per day level has more to do with deficiency prevention, not anti-aging or optimal health benefits.
There is some concern that doses higher than the UL of 40 mg per day might decrease copper absorption and result in anemia. However, there is some evidence doses of elemental zinc as high as 80 mg daily in combination with 2 mg of copper can be used safely for approximately six years without significant adverse effects. There is not a shred of evidence that doses of 40 mg per day have any deleterious effects.
Dr. Rona
References
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002. Available at: www.nap.edu/books/0309072794/html/.
Age-Related Eye Disease Study Research Group. "A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta-carotene, and zinc for age-related macular degeneration and vision loss." AREDS report no. 8. Arch Ophthalmol 2001;119:1417-36.7304
