Vitamin C and Cancer

The Food and Drug Administration doesn’t require proof that dietary supplements are safe or effective, as long as they don’t claim that the supplements can prevent, treat, or cure any specific disease; and most supplements have not been tested to find out how they interact with medicines, foods, or other herbs and supplements.  Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects aren’t often available.
Vitamin C supplements are generally considered safe.  Doses higher than 1,000 mg can cause diarrhea, nausea, heartburn, belly pain, and stomach cramps in some people, but the safe upper limit of vitamin C for adults is considered to be about 2,000 mg.  Most oncologists routinely recommend that people with cancer avoid gram-size doses of vitamin C during treatment.
Vitamin C is an essential vitamin the human body needs to function well.  It is a water-soluble vitamin that cannot be made by the body, and must be obtained from foods or other sources. Many studies have shown a link between eating foods rich in vitamin C, such as fruits and vegetables, and a reduced risk of cancer.
Vitamin C is also an antioxidant, a compound that helps block the action of unstable molecules known as free radicals, which can damage cells.  Vitamin C is thought by some to enhance the immune system by stimulating the activities of natural killer cells and anti-cancer agents.  Some claim that the vitamin can prevent a variety of cancers from developing, including lung, prostate, bladder, breast, cervical, intestinal, esophageal, stomach, pancreatic, and salivary gland cancers, as well as leukemia and non-Hodgkin’s lymphoma.  Vitamin C is also said to prevent tumors from spreading, help the body heal after cancer surgery, enhance the effects of certain anti-cancer drugs, and reduce the toxic effects of other drugs used in chemotherapy.
Vitamin C is water-soluble, which means that the body uses what it needs and eliminates the rest.  Small amounts of vitamin C are needed for healthy skin, tendons, ligaments, bones, cartilage, and blood vessels, and for the healing of wounds and injuries.  It also helps to body absorb iron from foods.  A shortage of vitamin C causes scurvy, a disease marked by fatigue, fragile blood vessels bleeding, which can be fatal if not treated.  Vitamin C deficiency is very rare among people who eat a reasonably balanced diet.
Many scientific studies have shown that diets high in fruits and vegetables reduce the risk of developing cancers of the pancreas, esophagus, larynx, mouth, stomach, colon and rectum, breast, cervix, and lungs.  Many of these studies show people who eat foods to get a high level of vitamin C have about half as much cancer as those who have a low intake of these foods. Likewise, people with higher blood levels of vitamin C tend to have a lesser risk of developing cancer than do people with lower levels.  However, studies that observed large groups or people and clinical trials of vitamin C supplements have not shown the same strong protective effects against cancer.
Some oncologists believe that taking high doses of antioxidant vitamins may actually interfere with the effectiveness of radiation and some chemotherapy drugs.  However, no randomized clinical trials have yet been done in humans to test the effect of Vitamin C supplements during radiation therapy or chemotherapy.  Although high doses of vitamin C have been suggested as a cancer treatment, the available evidence from clinical trials has not shown any benefit.
The American Cancer Society recommends eating a variety of healthful foods, with most of them coming from plant sources, rather than supplements. It’s best to get vitamins and minerals from foods but supplements may be helpful for some people, such as pregnant women, women of childbearing age, and people with restricted food intakes.   If a supplement is taken, choose a balanced multivitamin/mineral supplement that contains no more than 100% of the “Daily Value” of most nutrients.