Humans need vitamin C to maintain healthy collagen -- tissues found throughout your body in your skin, bones and blood vessels -- and to augment your immune system. When you're low in vitamin C, you may catch colds more easily, and you may find that minor cuts and bruises don't heal as quickly as they should. Unfortunately, you can't store vitamin C, so you need to obtain all the vitamin C you need from your daily diet. The U.S. Department of Agriculture doesn't recommend taking massive amounts of vitamin C -- more than 2,000 mg per day -- because you might experience gastrointestinal side effects from that high a dose.
Basics
The Recommended Dietary Allowance for vitamin C varies by age. For infants and children between birth and 18 years, the RDA ranges between 15 mg and 75 mg, depending on age and sex. Adult men should obtain 90 mg of vitamin C each day, while women need 75 mg unless they're breastfeeding, in which case they need 120 mg. Smokers should take an additional 35 mg a day, since smoking tends to deplete your stores of vitamin C.
Effects
You can consume as much vitamin C as you wish from food sources and not risk adverse effects. However, massive doses of vitamin C from supplements -- defined by the U.S. Department of Agriculture as more than 2,000 mg a day -- potentially can cause gastrointestinal upset, including diarrhea, gas and a sour stomach. Research in baby chickens indicates that taking large doses of the vitamin potentially can draw calcium from your bones, resulting in a weakened skeletal system. However, that research hasn't been duplicated in humans.
More Effects
It's possible that massive doses of vitamin C ranging from 1,000 mg to 15,000 mg daily can increase your risk of kidney stones and gout, although more research would be needed to establish a clear link. Massive doses of vitamin C can increase your urinary oxalate levels, and high urinary oxalate levels potentially can promote kidney stone formation. However, not all researchers have identified an increased risk of kidney stones related to vitamin C supplementation. Likewise, although some research points to a link between heightened levels of uric acid spurred by vitamin C supplementation and gout, other studies find a lower risk of gout in people taking more vitamin C.
Considerations
Dr. Linus Pauling, a renowned biologist and vitamin C researcher, recommended very high vitamin C intakes; in fact, he said that all adults should get at least 250 mg a day, and that 2,000 mg represented the optimal intake, not the tolerable upper limit as the USDA stipulates. However, the Linus Pauling Institute at Oregon State University, which bears his name, says that your body can't utilize more than 400 mg of vitamin C each day and excretes any additional vitamin C in the urine, although the Institute also notes that some people, especially the elderly, may need to take more vitamin C. If you're wondering how much vitamin C to take, you should discuss your concerns with your physician.
References
- University of Maryland Medical Center; Vitamin C (Ascorbic Acid); June 18, 2009
- Vanderbilt University; Vitamin C in Treatment of The Common Cold; Dawn Myers
- Oregon State University Linus Pauling Institute; Vitamin C; Jane Higdon, Ph.D.; November 2009
- Oregon State University Linus Pauling Institute; The Difference Between Dr. Linus Pauling's Recommendations and the Linus Pauling Institute's Recommendation for Vitamin C Intake; Jan. 27, 2004
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