Vitamin C

Last Updated: November 20, 2023

Vitamin C, or ascorbic acid, is an essential vitamin and a very popular supplement due to its antioxidant properties, safety profile, and low price. Many people supplement with vitamin C because it is believed to reduce symptoms of the common cold.

Vitamin C is most often used for

What is vitamin C?

Vitamin C is a water-soluble essential vitamin that can be found in fruits and vegetables, especially citrus. Humans are unable to synthesize vitamin C from their bodies, so it must be acquired through dietary intake. Vitamin C is important for immune system function and is a powerful antioxidant. It also acts as a cofactor for collagen synthesis.[2]

What are vitamin C’s main benefits?

People often supplement with vitamin C when they have a cold. According to various studies, vitamin C may be effective in reducing the duration of a cold, but does not seem to reduce the frequency of colds in a population.[3][4] The available literature suggests that a dose ranging from 200 mg to 2,000 mg could be beneficial for reducing cold duration.

Often utilized for its antioxidant effects, vitamin C has been studied for its potential role in Alzheimer’s disease and cancer. Lower vitamin C levels are present in people with Alzheimer’s, even with adequate dietary intake.[5] It is thought that oxidative stress plays a major role in the pathogenesis of the disease, so vitamin C’s antioxidative effects could be beneficial.[6][7] In rodent studies, oral vitamin C was able to reduce oxidative and inflammatory biomarkers.[8] In recent cancer research, vitamin C was found to promote oxidative stress in cancer cells, leading to cytotoxic effects at high doses in mice.[9] While promising, further research and human studies are required to determine efficacy.

What are vitamin C’s main drawbacks?

In general, vitamin C supplementation at recommended doses seems to be safe. However, higher doses (3,000–10,000 mg) may cause diarrhea.[2] One meta-analysis noted an increased risk of dental erosion with chewable vitamin C tablets.[10] A rare but noteworthy possibility of nephrotoxicity after high dose administration has also been observed,[11][12] but this is unlikely to occur with typical oral supplementation.

How does vitamin C work?

Vitamin C acts as a cofactor for various enzymes, notably enzymes involved in collagen synthesis, and as an antioxidant.[13] It is an essential vitamin that humans cannot synthesize, so it must be acquired through dietary intake. Deficiencies in this vitamin results in scurvy, a condition caused by a lack of vitamin C.[13]

What are other names for Vitamin C?
Note that Vitamin C is also known as:
  • Ascorbic Acid
  • Ascorbate
  • L-ascorbic acid
Vitamin C should not be confused with:
Dosage information

According to the WHO, most adults need only 45 mg of vitamin C per day, but more recent research has shown this number to be too low. The minimum has been set at 75 mg for women and 90 mg for men in the U.S., and 95 mg for women and 110 mg for men in the E.U.

Moreover, a 2022 study using 110 mg as its starting number recommended adding 10 mg per 10 kg (22 lb) above 60 kg (132 lb) of body weight.[1]

Any of these numbers are easily attained through the diet, so supplementation of such low doses is usually unnecessary. Higher doses of vitamin C, up to 2,000 mg, are used to support the immune system (for athletes) or reduce the duration of the common cold.

Most studies on vitamin C prescribe one dose per day. The claim that taking 2,000 mg up to five times a day to optimally reduce cold symptoms is not sufficiently tested and requires more evidence.

Examine Database: Vitamin C