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 D.

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 cancer.

Analysis showed that, for at least some cancers, the vitamin D factor could not be ignored.