Review finds vitamin D could prevent significant number of cancers
In a review that will appear in the February 2006 issue of The American Journal of Public Health vitamin D researcher Michael F. Holick and colleagues concluded that improved vitamin D status could significantly cut the risk of colon, breast, ovarian and prostate cancer. A previous review conducted by the team, published in the October 2005 Journal of Steroid Biochemistry and Molecular Biology found that consuming 1000 international units (IU) or more of vitamin D per day cut the risk of colon cancer in half.
The team reviewed 63 studies of oral intake or serum levels of vitamin D as related to the risk of cancer published between January 1966 and December 2004. The majority revealed a protective effect for the vitamin. The authors attribute vitamin D’s benefits to its abilities to inhibit the formation of new blood vessels by tumors, stimulate mutual adherence of cells, and enhance intercellular communication. They also note that having higher serum vitamin D levels is associated with reduced proliferation of high-risk epithelial cells in the colon and that the vitamin helps prevent breast epithelial cell mitosis.
The authors observed that vitamin D doses of up to 1000 IU per day are unlikely to produce toxicity and comment that this dose would be consistent with maintaining serum vitamin D levels at or above 30 nanograms per milliliter. Serum levels of vitamin D lower than 30 ng/mL have been associated with double the risk of colon cancer than that experienced by individuals with higher levels.
The review concludes that “Supplemental vitamin D intake could address the high prevalence of vitamin D deficiency in the United States... The cost of a daily dose of vitamin D3 (1000 IU) is less than 5 cents, which could be balanced against the high human and economic costs of treating cancer attributable to insufficiency of vitamin D.”
Coauthor Cedric F. Garland, who is a professor at the University of California, San Diego School of Medicine’s Department of Family and Preventive Medicine, commented, “A preponderance of evidence, from the best observational studies the medical world has to offer, gathered over 25 years, has led to the conclusion that public health action is needed. Primary prevention of these cancers has largely been neglected, but we now have proof that the incidence of colon, breast, and ovarian cancer can be reduced dramatically by increasing the public's intake of vitamin D."
"Many people are deficient in vitamin D,” he added. “A glass of milk, for example, has only 100 IU. Other foods, such as orange juice, yogurt and cheese, are now beginning to be fortified, but you have to work fairly hard to reach 1,000 IU a day. Sun exposure has its own concerns and limitations . . . The easiest and most reliable way of getting the appropriate amount is from food and a daily supplement.
In a population-based case-control study of 105 cases of colorectal adenoma, serum concentrations of vitamin A were significantly inversely related to the risk of colorectal adenoma when cases were compared with the control group. The risk of developing colorectal adenomas was found to be reduced in those with high vitamin A levels (Breuer-Katschinski et al. 2001).
Retinol, retinoic acid, and beta-carotene (in nanomolar concentrations) block stimulation of protein kinase C (PKC), which when stimulated has been shown to increase tumor activity in the colon. It has been suggested that beta-carotene could be useful in the prevention and treatment of colorectal cancer (Kahl-Rainer et al. 1994), as beta-carotene has been shown to down-regulate growth factors which contribute towards proliferation of premalignant cells. Combined, vitamin A and vitamin D3 have been shown to inhibit tumor-induced angiogenesis (Majewski et al. 1996).
Convincing evidence is available showing that dietary calcium and vitamin D impede the development of colonic carcinogenesis (Lamprecht et al. 2001). Calcium supplementation and vitamin D both appear to have antineoplastic effects in the large bowel; they appear to act together to reduce the risk of colorectal adenoma recurrence (Grau et al. 2003). Additionally, dietary vitamin D3 impedes the neoplastic process in murine large intestine (Mokady et al. 2000) and vitamin D3 has demonstrated the ability to inhibit liver cancer cell growth (Alvarez-Dolado et al. 1999; Majewski et al. 1996).
A dietary deficiency of vitamin D inhibits the production of the protein that binds calcium in the intestines, so that calcium cannot be absorbed, even if there is adequate intake. Deficiencies of vitamin D are often found in the elderly and in women who have low intake of milk and receive inadequate exposure to sunlight. Vitamin D is potent in minute quantities; one microgram of cholecalciferol has 40 IU of vitamin D activity.
Calcium is an essential mineral that is often inadequately supplied, inefficiently absorbed, or excreted faster than it is being assimilated. The citrate salt of calcium has been documented to be well absorbed and utilized by the body.