Vitamin D 'can lower cancer risk'High doses of vitamin D can reduce the risk of developing some common cancers by as much as 50%, US scientists claim.
Researchers reviewed 63 old studies and found that the vitamin could reduce the chances of developing breast, ovarian and colon cancer, and others.
Experts said more research was needed to draw firm conclusions.
Charities cautiously welcomed the University of California study but warned too much vitamin D could harm the kidneys and liver.
The "natural" form of the vitamin, called D3, is normally produced in the skin after exposure to sunlight, but is also obtained from certain foods such as oily fish, margarine and meat.
The research, done at the University of California in San Diego, looked at the relationship between blood levels of vitamin D and cancer risk.
Survival rates for Afro-Caribbean people with breast, colon, prostate and ovarian cancers are worse than for white people, possibly because dark skins are not as good at making vitamin D, the researchers said.
The papers reviewed, published worldwide between 1966 and 2004, included 30 investigations of colon cancer, 13 of breast cancer, 26 of prostate cancer and seven of ovarian cancer.
Scientists said analysis showed that, for at least some cancers, the vitamin D factor could not be ignored.
Taking 1,000 international units (IU) - or 25 micrograms - of the vitamin daily could lower an individual's cancer risk by 50% in colon cancer, and by 30% in breast and ovarian cancer, they said.