A large daily dose of vitamin D can lower the risk of developing common
cancers by as much as 50%, scientists said.
Researchers found that the "natural" form of the vitamin, known as
D3, can dramatically reduce the chances of developing breast, ovarian and colon
cancer, as well as others.
Taking 1,000 international units (IU) of the vitamin daily could lower an individual's
cancer risk by 50%, they said.
Such large doses of vitamin D must be treated with caution. More than 2,000
IU a day can lead to the body absorbing too much calcium, and possible damage
to the liver and kidneys.
D3 is normally produced in the skin by the action of sunlight, but is also
obtained from certain foods.
Dietary sources are limited, however. A glass of milk, for instance, contains
only 100 IU of the vitamin.
Survival rates for Afro-Caribbean people with certain cancers are worse than
for white people, possibly because dark skins are not as good at making vitamin
The US researchers carried out a systematic review of 63 studies looking at
the relationship between blood levels of vitamin D and cancer risk.
The papers, published worldwide between 1966 and 2004, included 30 investigations
of colon cancer, 13 of breast cancer, 26 of prostate cancer and seven of ovarian
Analysis showed that, for at least some cancers, the vitamin D factor could
not be ignored.