The finding of researchers from the Moore's Cancer Center at the University of California, San Diego indicated an association between reduced sunlight exposure and a greater incidence of kidney cancer. Now, in an article that will be published online in the American Journal of Preventive Medicine, the UCSD team reports that women exposed to a greater amount of sunlight, particularly ultraviolet B (UVB) radiation, have a lower incidence of ovarian cancer. UVB exposure stimulates the synthesis of vitamin D in the body, however, the vitamin is also obtainable via the diet and/or supplementation.
UCSD School of Medicine professor of Family and Preventive Medicine Cedric F. Garland, Dr PH, and colleagues utilized a database of cancer incidence, mortality, and prevalence in 175 countries, recently made available from the World Health Organization's International Agency for Research on Cancer. By graphing ovarian cancer incidence rates according to latitude, the team was able to demonstrate an association between higher latitudes, which receive reduced sunlight, and ovarian cancer. Additionally, greater fertility rates among women between the ages of 15 and 19, which may be protective against ovarian cancer, were more prevalent in lower latitudes.
"In general, ovarian cancer incidence was highest at the highest latitudes in both hemispheres," Dr Garland stated. "They were about five times higher in high latitudes, like Iceland and Norway, than in equatorial regions like Asia, South America and Africa. Even after controlling for fertility, the association remained strong."
"Unlike breast cancer, we have no widely accepted means of early detection or prevention for ovarian cancer," Dr Garland observed. "This new global study shows a link between deficiency of vitamin D and increased incidence of ovarian cancer, suggesting that vitamin D supplementation may reduce the incidence of this aggressive cancer."
Approximately 15,300 deaths from ovarian cancer occur in the United States each year.
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Evidence points to a prostate, breast, and colon cancer belt in the United States, which lies in northern latitudes under more cloud cover than other regions (Studzinski et al. 1995). Certain regions in the United States, such as the San Joaquin Valley cities and Tucson, AZ; Phoenix, AZ; Albuquerque, NM; El Paso, TX; Miami, FL; Jacksonville, FL; Tampa, FL; and Orlando, FL; have a lower incidence of breast and bowel cancers. Conversely, New York; Chicago; Boston; Philadelphia; New Haven, CT; Pittsburgh; and Cleveland, OH; have the highest rates of breast and intestinal cancer of the 29 major cites in the United States. The greater hours of year-round sunlight correlate to a lower rate of breast and intestinal cancer in the U.S.A.
Vitamin D is formed in the skin of animals and humans by the action of shortwave UV light, the so-called fast-tanning sunrays. Precursors of vitamin D in the skin are converted into cholecalciferol, a weak form of vitamin D3, which is then transported to the liver and kidneys where enzymes convert it to 1,25-dihydroxycholecalciferol, the more potent form of vitamin D3 (Sardi 2000). Although vitamin D exists in two molecular forms, vitamin D3 (cholecalciferol) found in animal skin and vitamin D2 (ergocalciferol) found in yeast, vitamin D3 is believed to exhibit more potent cancer-inhibiting properties and is therefore the preferred form.
Dark-skinned people require more sun exposure to produce vitamin D because the thickness of the skin layer (the stratum corneum) affects the absorption of UV radiation. Black human skin is thicker than white skin and thus transmits only about 40% of the UV rays needed for vitamin D production. Darkly pigmented individuals who live in sunny equatorial climates experience a higher mortality rate from breast and prostate cancer when they move to geographic areas that are deprived of sunlight exposure in winter months (Angwafo 1998; Sardi 2000).