Vitamins - Dietary Health Benefits

(Page 3)

Additionally, certain supplements may actually encourage tumor growth.

Vitamins and Cancer Protection. Because many cancers are thought to be initiated by the effects of oxygen-free radicals on DNA, the antioxidants A, C, and E and beta-carotene have been intensively studied. Beta-carotene supplementation increases lung cancer risk in smokers and persons exposed to asbestos.

In 2006, a study for the National Institutes of Health reviewed randomized trials evaluating the effectiveness and safety of multivitamin and mineral supplements in preventing cancer and chronic disease. The reviewers concluded that current evidence is not sufficient to determine that multivitamin and mineral supplements prevent cancer or chronic disease.

---

---

Carotenoids and Cancer Protection. A number of studies have reported that fruits and vegetables rich in carotenoids may protect against many cancers. Lycopene, found in tomatoes, may protect against prostate, colon, lung, and bladder cancers. Supplements, however, do not offer any advantage.

Phytochemicals and Cancer Protection. The following phytochemicals appear to have cancer-protective properties.

• Isothiocyanates. Isothiocyanates and sulforaphane, found in cruciferous vegetables, may block the effects of carcinogens and suppress tumor growth.
• Isoflavones. Isoflavones are found in soybeans and flaxseed. Studies on isoflavones and cancer risk have been mixed. Some studies have linked a higher intake of soy with a lower incidence of reproductive and breast cancers. Some evidence suggests the genistein in soy may offer some protection against lung cancer. Nonfermented soy products (tofu, soy milk) also may protect against stomach cancer, while fermented soy products (miso, soy paste) appear to increase the risk.
• Organosulfurs. The organosulfur compounds found in the onion and garlic family may have very potent properties in suppressing or blocking cancer-causing substances. One possible explanation for garlic's anti-cancer effect in the stomach is its antibacterial action against H. pylori bacteria, which can promote colon adenomas (polyps that may become cancerous).