San Diego: Scientists at the University of California say that large doses of vitamin D each day can halve the chance of developing cancer.
They recommend a daily dose of 25 microgrammes. Vitamin D is found in oily fish, meat, eggs, milk and cod liver oil.
Multivitamin pills contain about a quarter of the amount, though there are higher levels in cod liver oil capsules and combined vitamin D and calcium pills. Sunbathing also boosts levels as vitamin D is made in the body in response to sunlight. But there are dangers in over-exposure, with fair-skinned people in particular advised to stick to food sources.
The report follows research indicating that good levels of vitamin D can prevent more than 25 chronic diseases.
In the latest research it was found after reviewing 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, says a report in the American Journal of Public Health.
Professor Cedric Garland, of the Moores Cancer Centre at the University of California, San Diego, called for urgent public health action.
He said: ‘Primary prevention of these cancers has largely been neglected, but we now have proof that the incidence of colon, breast, and ovarian cancer can be reduced dramatically by increasing the intake of vitamin D.
‘Breast cancer will strike one in eight women. Early detection using mammography reduces mortality rates by approximately 20 per cent, but the use of vitamin D might prevent this cancer in the first place.’
Professor Garland said a lack of vitamin D could explain the high death rates from cancer among certain groups.
The study found that people in the north- eastern U.S. were at increased risk because of lower sunlight levels. Poorer cancer survival rates among African-Americans may be because it is more difficult for dark-skinned people to make the natural form of the vitamin, known as D3.
The new results will add to a recent surge of interest in vitamin D for cancer prevention and possible treatment.
Earlier this year, Professor Johan Moan of the Institute for Cancer Research, in Oslo, studied all the people diagnosed with cancer in Norway between 1964 and 2000. He found the risk of dying within three years was 50 per cent lower for those diagnosed during summer and autumn – when blood levels of vitamin D are highest – than in winter.
Professor Moan said: ‘In Nordic countries, and in Britain, practically no vitamin D is generated in the skin during the winter because solar radiation contains too little ultraviolet B. In wartime Britain, children were regularly given cod liver oil for extra vitamins.’