Supplementation with 1,000IU of vitamin D3 daily could reduce the incidence of colon, breast, prostate and ovarian cancer, at low cost and with few adverse effects, according to researchers at the Moores Cancer Centre, University of California, San Diego.
They conducted a systematic review of 63 observational studies of vitamin D status in relation to cancer risk. The review included 30 studies of colon cancer, 13 of breast, 26 of prostate and seven of ovarian cancer. The researchers found that most studies showed a protective relationship between adequate vitamin D levels and risk of cancer.
The review also highlighted that African-Americans, who have higher rates of mortality for colon, breast, prostate and ovarian cancer, have approximately half the plasma level of vitamin D as white people because increased skin pigmentation reduces their ability to synthesise vitamin D.
The researchers say that a dose of 1,000IU of vitamin D3 (25µg) daily should maintain serum levels of vitamin D at or above 30ng/ml in most people. Throughout the US, exposure to sunlight for 15 minutes per day between 11am and 2pm, in the summer, under clear skies, should maintain a similar level. However, the researchers warn that if sunlight is used as a source of vitamin D, exposure should be scrupulously monitored so that no reddening of the skin occurs. “Oral vitamin D3 supplementation, rather than solar exposure, should be used by fair skinned or sun-sensitive persons, or by individuals taking medicines causing photosensitivity.” They add that according to the National Academy of Sciences, no known health risks are associated with doses of vitamin D up to 2,000IU daily.
“Strong evidence indicates that intake or synthesis of vitamin D is associated with reduced incidence and death rates of colon, breast, prostate and ovarian cancers,” they say. However, despite these reassuring studies, the public health and medical communities have failed to adopt its use for cancer prevention, they point out. “Leadership from the public health community will provide the best hope for action,” they conclude (American Journal of Public Health 2006;96:9).