Vitamin C, available in several foods and dietary supplements, shows some anticancer effects, including better survival among people with breast cancer.
Oral vitamin C at a glance
Vitamin C, also called ascorbic acid or ascorbate, is an essential nutrient for growth, development, and healing. A deficiency is linked to increased risk of several diseases, including cancer as a whole and many types of cancer.
Humans cannot produce vitamin C, so we need to get it from foods or supplements. Although vitamin C is usually associated with citrus fruits, it’s found in many other foods:
- Cruciferous vegetables, including cabbage, Brussels sprouts, and broccoli
Vitamin C dissolves in water and is destroyed by high heat. Therefore, vitamin C levels will be lower if foods are cooked, especially if cooked in water.1The Nutrition Source. Vitamin C. Harvard T. H. Chan School of Public Health. March 2023. Viewed April 10, 2023.
A diet high in refined foods and processed sugar can inhibit the absorption of vitamin C,2Kaźmierczak-Barańska J, Boguszewska K, Adamus-Grabicka A, Karwowski BT. Two faces of vitamin C—antioxidative and pro-oxidative agent. Nutrients. 2020 May 21;12(5):1501. and people who smoke are at higher risk of vitamin C deficiency.3Schectman G, Byrd JC, Gruchow HW. The influence of smoking on vitamin C status in adults. American Journal of Public Health. 1989 Feb;79(2):158-62. People with leukemia are also at risk of vitamin C deficiency.4Milbar HC, Caplan A et al. Vitamin C deficiency in patients with acute myeloid leukemia: a case series and review of the literature. Blood Advances. 2023 Oct 10;7(19):5780-5783.
Oral vitamin C is also available as a dietary supplement. Oral intake of vitamin C, from either diet or supplements, shows some anticancer effects, including better survival among people with breast cancer. However, research also shows that higher intake of vitamin C is linked to higher risk of liver cancer or melanoma and possibly slightly higher risk of recurrence or diagnosis of breast cancer, rectal cancer, and gastrointestinal cancer. High oral doses can lead to serious side effects. Even though vitamin C supplements are readily available at low cost, we recommend professional guidance in using supplements.
Intravenous vitamin C is another therapy used among people with cancer. We review it separately due to its different benefits, safety issues, access, and affordability.
CancerChoices ratings for oral vitamin C
We rate oral vitamin C on seven attributes, with 0 the lowest rating and 5 the highest. We rate the strength of the evidence supporting the use of oral vitamin C for a medical benefit, such as improving treatment outcomes or managing side effects.
See how we evaluate and rate complementary therapies ›
Keep reading about oral vitamin C