Vitamin C toxicity is very rare. Some people take high doses of vitamin C because it is an antioxidant.
Some people take high doses of vitamin C because it is an antioxidant, which protects cells against damage by free radicals. Free radicals are thought to contribute to many disorders, such as atherosclerosis, cancer, lung disorders, the common cold, and memory loss. However, whether taking high doses of vitamin C protects against or has any beneficial effect on these disorders is unclear; most studies have shown no benefit. Evidence of a protective effect against cataracts is strongest.
High doses (up to the safe upper limit—2,000 milligrams a day) of vitamin C are usually not toxic to healthy adults. Occasionally, higher doses cause nausea or diarrhea and interfere with the balance of antioxidant activity in the body.
