Vitamins and minerals are necessary for good health. They are often referred to as micronutrients, because they are found in relatively small amounts in foods and body tissues. Many vitamins and minerals have been studied in cancer prevention. Vitamins and minerals include:
- Vitamin A
- Thiamin
- Riboflavin
- Niacin
- Vitamin B6
- Vitamin B12
- Vitamin C
- Vitamin D
- Vitamin E
- Vitamin K
| - Folic acid
- Pantothenic acid
- Biotin
- Calcium
- Zinc
- Copper
- Chromium
- Manganese
- Selenium
|
Antioxidants
All cells in the body are exposed to oxidants, which are substances that can damage the body’s cells. Cigarette smoke and ozone are examples of oxidants. The body has an antioxidant defense system that protects against damage from these substances. In addition, many vitamins and minerals are antioxidants, and it is possible that adding these to a person’s diet lowers the risk of diseases, including cancer.
Vitamins, minerals, and other nutrients that are part of the antioxidant defense system include:
- Vitamin E
- Carotenoids (chemicals that give fruits and vegetables an orange or yellow color), such as beta-carotene and lycopene
- Vitamin C
- Selenium
- Other plant chemicals, such as flavonoids
Other nutrients may directly or indirectly provide antioxidant activity, although these have not been studied as much for cancer prevention.
Antioxidants and cancer prevention
Although multiple laboratory studies have shown that these vitamins and minerals are antioxidants, it has been more difficult to prove they can prevent cancer in people. A review of current research shows the following:
Beta-carotene. High-dose supplements containing beta-carotene do not seem to prevent cancer. In studies of current and former smokers, high-dose beta-carotene supplements actually raised the risk of lung cancer.
Vitamin C. Many studies show that higher amounts of vitamin C in the diet are associated with a lower risk of stomach cancer; however, this result was not confirmed in a recent clinical trial (a research study involving people).
Vitamin E. In a clinical trial regarding supplements and lung cancer, researchers unexpectedly found that vitamin E seemed to lower the number of new cases of prostate cancer. Additional studies show that vitamin E lowers risk of prostate cancer only in current smokers or those who recently quit. A large clinical trial called the Selenium and Vitamin E Cancer Prevention Trial (SELECT) is further testing the relationship between vitamin E and prostate cancer, but was stopped in October 2008 for safety concerns. More information about the SELECT clinical trial is below.
Selenium. Selenium has been identified as a potential cancer prevention micronutrient because people who didn’t get enough selenium seemed to be at higher risk for cancer. In a study of skin cancer, selenium didn’t prevent a second skin cancer in people who already had skin cancer, but it lowered the new cases of prostate, lung, and colorectal cancers. However, these benefits may only be in people who do not get enough selenium in their diet.
Before taking any dietary supplements or antioxidants, it is important to talk with your doctor, as these supplements may interfere with cancer treatment.
SELECT clinical trial
SELECT is a clinical trial studying selenium and vitamin E for prostate cancer prevention. More than 35,000 men age 55 and older are participating, 15% of whom are black men, which is important because black men have a higher overall risk of prostate cancer. The men in the study received one of the following treatments: vitamin E only, selenium only, both vitamin E and selenium, or no supplements (called the control group). After five years, results showed that selenium and vitamin E, taken alone or together for an average of five years, did not prevent prostate cancer. In addition, the National Cancer Institute has suspended the study because of data that showed that the supplements may cause harm. More information about SELECT is available at http://www.cancer.gov/newscenter/pressreleases/SELECTQandA.
Women’s Health Initiative (WHI) study
Calcium and vitamin D have been studied for the prevention of colorectal cancer, usually by measuring the formation of adenomas (potentially precancerous polyps) in people with a history of adenomas. These nutrients are tested together because vitamin D is necessary for calcium to be absorbed by the body.
The WHI was a large study of more than 36,000 postmenopausal women. One part of the study tested whether daily supplements of calcium and vitamin D could prevent colorectal cancer. After seven years, researchers found that supplemental calcium and vitamin D had no effect on the number of new cases of colorectal cancer. But, it is possible that the effect of these nutrients couldn’t be seen in seven years’ time.
Folate
Folate is a generic description of a water-soluble B vitamin that is found in foods such as leafy, green vegetables, fruit, and dried beans and peas. Folic acid, a close relative, is a form of folate made in the laboratory that is found in supplements and fortified foods, such as breads and cereals. Folate plays an important role in the health of cells, and studies show that people with low levels of folate have an increased risk of breast, colon, and pancreatic cancers. Folate is also known to counteract the effect of alcohol.
So far, studies in people have not shown a relationship between folic acid and cancer prevention. Several other clinical trials are in progress to answer this question. It may be likely that folate from food may be a better source for the body than folic acid supplements.
Vitamins, minerals, and survivorship
Many cancer survivors want information on healthy eating and the use of vitamins and minerals to help lower the risk of the cancer returning. However, in the studies to date, there is no clear evidence that any particular vitamin or mineral helps prevent a second cancer. Part of the reason for this may be because people have different health histories and different habits regarding nutrition, tobacco use, and exercise. Dietary recommendations for cancer survivors are similar to those for the general population, and include quitting smoking, avoiding weight gain, being physically active, limiting alcohol, and eating more plant-based foods. Learn more about Dietary Recommendations During and After Treatment. More Information
Prevention: Chemoprevention
Prevention: Plant-based Foods
Treatment: Complementary and Alternative Medicine
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