Initial Posting: 6/3/2015    Last Update: 12/9/2018
Answer: Yes, it's possible to take too much vitamin C. Since vitamin C is water-soluble, as are B vitamins (i.e. excess amounts are excreted and do not accumulate in the body), people sometimes assume there is no harm in taking large doses. However, there are potential short-term and long-term problems with taking high doses (500 to 1,000 mg per day) or very high doses (more than 2,000 mg per day) of vitamin C.
Very high doses of vitamin C are known to cause gastric discomfort and diarrhea, and this is the basis for the current upper tolerable daily intake limit of 2,000 mg for adults.
More limited, but concerning, evidence suggests problems with daily doses of just 500 to 1,000 mg of vitamin C. (Keep in mind that the recommended daily intake of vitamin C for adults is only 75 mg to 120 mg, with an additional 35 mg for smokers -- see the RDAs for details).
For example, while long-term, low-dose supplementation with vitamin C may help to prevent cataracts, high doses may actually increase the risk. Taking several hundred milligrams of vitamin C daily may also hamper some of the benefits of endurance exercise, as has been found with high doses of other antioxidant vitamins and supplements, such as vitamin E and resveratrol.
High doses of vitamin C may also reduce the effectiveness of certain medications, and increase the risk of liver damage when taking high doses of Tylenol. They may also interfere with tests for cholesterol and blood sugar, and for blood in the stool.
Individuals prone to developing kidney stones or with defects in metabolizing vitamin C or oxalate should also limit vitamin C from supplements.