Cancer of the colon or rectum is the second deadliest form of cancer. About 55,000 Americans die from the disease each year. It is also considered one of the most preventable types of cancer, as there are several dietary factors that appear to play a protective role. In one of the most comprehensive studies to date on colon-cancer risk, a team led by the National Cancer Institute and Harvard, researchers confirmed that proper intake of vitamin D is associated with reduced risk of serious colon polyps that may lead to colon cancer. In the study those who consumed higher amounts of vitamin D -- more than 645 international units (IUs) per day -- were significantly less likely to have serious colon polyps, or tumors, which are often the precursor to cancer.
However, prevention of colon cancer is only one of the relatively minor benefits of vitamin D as it has dramatic influence on breast and prostate cancer, which are the most common cancers in men and women. Omega-3 fats are also exceptional in reducing these cancers so it makes perfect sense to start using cod liver oil, if you haven't started already as it is chock full of life enhancing omega-3, and the natural forms of vitamin D and vitamin A.
JAMA December 10, 2003;290(22):2959-296