Health effects from ingesting too much vitamin C

Originally Published: August 22, 2003
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Dear Alice,

What happens if you got too much vitamin C?

Dear Reader,

Vitamin C, also known as ascorbic acid, is one of the most commonly taken supplements in the United States. Generally, it is safe, but avoid taking large doses of this vitamin. As a matter of fact, an Upper Limit was set in 2000 as part of the Dietary Reference Intakes (DRIs). For adults, this level was set at 2000 mg per day. Taking doses this large can result in diarrhea, stomach cramps, and nausea. These unpleasant symptoms are from the vitamin being unabsorbed in your intestinal tract. Besides, it's a waste to take such a large amount because the more vitamin C you take, the less your body absorbs.

Other purported possible side effects associated with high vitamin C intake include:

  • kidney stones
  • reduced Vitamin B-12 and copper status
  • increased oxygen demand
  • becoming a pro-oxidant (a substance thought to promote cancer, heart disease, and stroke, the opposite of an antioxidant)

The Food and Nutrition Board, the committee that sets the Recommended Dietary Allowances (RDAs) and DRIs, examined the evidence for each of these claims, but couldn't find enough research to prove any of them.

One noteworthy precaution is for people with hemochromatosis, an iron overload disease. Since vitamin C increases iron absorption, supplemental C is not recommended for them.

Alice