How Vitamin C Helps Protect Against Cancer

The Physicians Committee

How Vitamin C Helps Protect Against Cancer

Vitamin C is most famous for fighting colds, but its key role is in the formation of collagen, the most abundant protein in the human body, which is present in all types of connective tissue such as bones, cartilage, ligaments, and tendons. A lack of vitamin C can result in scurvy, a disease that causes bleeding, swollen gums and loose teeth resulting from the weakening of bones and connective tissue. Vitamin C is also extremely important for fighting cancer.1

Vitamin C, like some of the other nutrients, carotenoids and vitamin E, is an antioxidant that helps destroy cancer-causing free radicals in the body. The difference is that while vitamin E and carotenoids are fat-soluble, lodging themselves in the fatty layer of each cell membrane, vitamin C is water-soluble, protecting against oxidation in the watery areas such as blood and inside cells. It also helps to recycle vitamin E to keep it actively fighting free radicals. The protective effect of vitamin C has been shown for cancers of the esophagus, larynx, mouth, pancreas, stomach, colon, and breast.2,3

Food Sources

Humans, guinea pigs, the Indian fruit bat, and a handful of other species are the only mammals who cannot make their own vitamin C. These species are missing the enzyme necessary to produce the vitamin out of glucose found in the body. So we must be mindful to get it from food sources. Fortunately, that's easy to do. As long as you eat a variety of fruits and vegetables everyday, you should have no problem getting more than enough vitamin C. To achieve protection against cancer, vitamin C supplements are probably unnecessary. In fact, some studies have shown that excess vitamin C may cause kidney stones in individuals who are at risk.4

Here are some vitamin C-rich foods:

Food Vitamin C (mg/serving)

Broccoli, 1 cup raw, chopped

Cabbage, red, 1 cup, shredded 40

Cauliflower, 1 cup raw

Grapefruit, 1 pink or red 84
Guava, 1 medium 165
Kale, 1 cup cooked 68
Lemon, 1 medium 31
Orange, 1 medium 75
Pepper, hot chili, 1 109
Pepper, red sweet, 1 cup raw 90
Potato, 1 medium 26
Strawberries, 1 cup raw 84
Sweet Potato, 1 medium 28
Tomato, 1 medium 23
Source: Pennington, JAT. Bowes and Church's Food Values of Portions Commonly Used, 17th edition, Lippincott-Raven, 1998.

Tips for Increasing Vitamin C in Your Diet

  • Have a piece of citrus fruit for dessert. Just one orange takes care of a day's requirement for vitamin C.
  • Toss some peaches and berries into your cereal or pancakes.
  • Do not store your produce for too long. Vitamin C is one of the more unstable vitamins, and the longer you wait to eat your fruits and vegetables, the more it degrades and the more cancer-fighting power it loses.
  • Store produce at low temperatures.
  • Minimize cooking time. Cooking reduces the amount of vitamin C in most foods, with the possible exception of broccoli.2
  • Because vitamin C is water-soluble, steaming your vegetables or cooking them quickly in a small amount of liquid (instead of boiling them for longer periods of time) will minimize vitamin loss.

1. Luben R, Khaw KT, Welch A, et al. Plasma vitamin C in the EPIC-Norfolk cohort. Abstract from the European Conference on Nutrition and Cancer, Lyon, France, June 21-24, 2001: 35,
2. Combs GF. The Vitamins, Fundamental Aspects in Nutrition and Health. 2nd ed. San Diego, CA: Academic Press, 2001:245-272.
3. Block G. Vitamin C and cancer prevention: the epidemiological evidence. Am J Clin Nutr. 1991;53:270s-282s.
4. Rivers JM. Safety of high-level vitamin C ingestion. In: Elevated Dosages of Vitamins, Walter P, Stahelin H, and Brubacher G, eds. Lewiston, New York: Hans Huber Publications, 1989: 95-102.