Vitamin D likely responsible for decreased risk of advanced breast cancer in women with greater sun exposure
An article published online on October 12, 2007 the American Journal of Epidemiology revealed the finding of researchers from the Northern California Cancer Center, the University of Southern California, and Wake Forest University School of Medicine that increased levels of vitamin D in the body which are found among those with greater sunlight exposure are associated with a reduced risk of developing advanced breast cancer, defined as disease that has spread beyond the breast.
Esther John, PhD of Northern California Cancer Center and colleagues matched 1,788 Hispanic, African-American, and non-Hispanic White women with newly diagnosed breast cancer with 2,129 control subjects. To calculate sun exposure, the color of underarm skin, which is not usually directly exposed to sunlight, was classified as light, medium, or dark, and compared with the color of the forehead, which is normally exposed to the sun.
The team determined that light skinned women with the most exposure to the sun had half of the risk of developing advanced breast cancer than those whose exposure was low. Because the finding occurred in only one group of women, the researchers suggest that the effect was due to differences in vitamin D production. The effect was seen only in advanced and not localized breast cancer, which may mean that vitamin D slows the growth of breast cancer cells.
“We believe that sunlight helps to reduce women’s risk of breast cancer because the body manufactures the active form of vitamin D from exposure to sunlight,” Dr John stated. “It is possible that these effects were observed only among light- skinned women because sun exposure produces less vitamin D among women with naturally darker pigmentation.”
The authors do not recommend reducing breast cancer risk by sunbathing because the practice increases the risk of skin cancers. Rather, they suggest increasing the intake of the vitamin from fortified foods, fish, and supplements. “If future studies continue to show reductions in breast cancer risk associated with sun exposure, increasing vitamin D intake from diet and supplements may be the safest solution to achieve adequate levels of vitamin D,” stated coauthor Gary Schwartz, PhD, of the Comprehensive Cancer Center at Wake Forest University School of Medicine.
Co-researcher Sue Ingles, PhD added, “Since many risk factors for breast cancer are not modifiable, our finding that a modifiable factor, vitamin D, may reduce risk is important.”
A wide variety of factors may influence an individual's likelihood of developing breast cancer; these factors are referred to as risk factors. The established risk factors for breast cancer include: female gender, age, previous breast cancer, benign breast disease, hereditary factors (family history of breast cancer), early age at menarche (first menstrual period), late age at menopause, late age at first full-term pregnancy, obesity, low physical activity, use of postmenopausal hormone replacement therapy, use of oral contraceptives, exposure to low-dose ionizing radiation in midlife and exposure to high-dose ionizing radiation early in life.
Vitamin A and vitamin D3 inhibit breast cancer cell division and can induce cancer cells to differentiate into mature, noncancerous cells. Vitamin D3 works synergistically with tamoxifen (and melatonin) to inhibit breast cancer cell proliferation. The vitamin D-3 receptor as a target for breast cancer prevention was examined. Pre-clinical studies demonstrated that vitamin D compounds could reduce breast cancer development in animals. Furthermore, human studies indicate that both vitamin D status and genetic variations in the vitamin D-3 receptor (VDR) may affect breast cancer risk. Findings from cellular, molecular and population studies suggest that the VDR is a nutritionally modulated growth-regulatory gene that may represent a molecular target for chemoprevention of breast cancer (Welsh et al. 2003).
Daily doses of vitamin A, 350,000 to 500,000 IU were given to 100 patients with metastatic breast carcinoma treated by chemotherapy. A significant increase in the complete response was observed; however, response rates, duration of response and projected survival were only significantly increased in postmenopausal women with breast cancer (Israel et al. 1985).
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