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 Tolerable Upper Daily Intake Level 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. In addition, blood levels of vitamin C above what is considered adequate have been linked to increased risk of mortality. 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 RDA table below.
- Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes from the National Academies
- Daily Values from FDA Food Labeling: Revision of the Nutrition and Supplement Facts Labels 2016
- ULs (Tolerable Upper Intake Levels) from Dietary Reference Intakes (DRIs): Tolerable Upper Intake Levels, Vitamins from the National Academies
- * - Adequate Intake (AI)
- mg - milligram (1,000 milligrams = 1 gram)
- mcg - microgram (1,000 micrograms = 1 milligram)
- NE - DV not established
- ND - UL not determined
- m - male; f - female
- lact - lactating (breast feeding); preg - pregnant
- Age ranges are in years
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.
For more about these effects and the specific amounts of vitamin C associated with them, see the Concerns and Cautions section of the Vitamin C Supplements Review >>