Revealed: the best protection against cancer

Global study discovers astonishing power of vitamin made by the sun

Boosting levels of vitamin D could cut the incidence of breast cancer by a quarter, bowel cancer by a third and it should be offered to the population as part of a public health drive, scientists say.

The finding is based on a review of 2,750 research studies involving vitamin D, sometimes called "bottled sunshine", which show that taking daily supplements of the vitamin could do more for cancer prevention than a library full of lifestyle advice.

Vitamin D is made by the action of sunlight on the skin but the gloomy weather and long winter in countries north of 30 degrees latitude, such as the UK, means that a large part of the earth's population is deficient between October and March.

Vitamin D has attracted increasing attention in recent years as its role in preventing cancer and other conditions including heart disease, diabetes and multiple sclerosis, has been revealed. The weight of evidence has grown so dramatically that governments around the world are reviewing their recommendations. The US and Canadian governments have set up a taskforce on vitamin D, and the Scottish government is taking expert advice. The pressure is now on the Department of Health in England to respond.

Scotland's chief medical officer, Harry Burns, attended a conference last November convened by the Scottish government at which international experts recommended randomised trials be established in the wake of strong evidence that increased intake could improve health.

High rates of heart disease, cancer and multiple sclerosis in Scotland have been blamed on the weak sunlight and short summers. Some experts believe the benefits of the Mediterranean diet have as much to do with the sun as with the regional food. However, too much sun exposure leading to sunburn is damaging to the skin and a cause of malignant melanoma, one of the most rapidly growing – and deadly – cancers. Figures published this month show cases of melanoma have topped 10,000 annually for the first time.

Now scientists at the University of Edinburgh have been awarded a £225,000 grant to investigate the link between low levels of vitamin D in Scotland and bowel cancer.

The US and Canadian government taskforce is examining whether the current recommendation for people to achieve a blood level of vitamin D equivalent to taking 200-600 international units (IU) a day, depending on their age, should be increased. The recommended level was set in 1997 and is based on what was necessary for bone health, not cancer prevention.

The same level is recommended in the UK, where official policy is that sun exposure and diet (oily fish and eggs contain vitamin D) are sufficient to achieve it, without supplements, for most adults. But an increasing body of cancer and other medical experts say a healthy intake of vitamin D should be five to 10 times higher.

Writing in the Annals of Epidemiology, Professor Cedric Garland and colleagues from the University of California, San Diego, say if everyone took 2,000 IUs of vitamin D a day, the current maximum recommended in Canada, it would save an estimated 200,000 cases of breast cancer and 250,000 cases of bowel cancer worldwide.

Professor Garland first recognised the link when, as a young doctor in the late 1970s, he used to drive with his brother Frank Garland across the US from sunny California to John Hopkins University on the snowy east coast. Bowel cancer was more common in the north and east of the country than in the south and west and while cancer specialists at the time looked for an explanation in the amount of fibre in the diet or the way meat cooked on a barbecue, the Garland brothers suspected a link with climate.

Twenty-five years later, after a series of papers establishing the link between breast and bowel cancer and vitamin D, their ideas are being taken seriously. The Canadian Cancer Society was the first to recommend a daily vitamin D supplement (of 1,000 IUs) in 2007, for the whole country in winter and for northern parts that get little sun in summer as well.

However, the International Agency for Research on Cancer (IARC) in Lyons, France, called last year for a major trial to prove the safety and efficacy of vitamin D before supplements are recommended for populations.

IARC scientists have warned that high levels of vitamin D in blood samples may not prevent cancer but instead be a sign of a healthy lifestyle. Supplements have in the past failed to deliver the benefits expected from their naturally occurring versions, and have in some cases been found to be harmful. Beta-carotene, the precursor of vitamin A, which early research suggested would prevent lung cancer was shown to increase it in smokers.

But Oliver Gillie, of the Health Research Forum said vitamin D has also been shown to play a vital role in heart disease, cancer, diabetes, high blood pressure, schizophrenia and multiple sclerosis. "It is like the trick question whether it was Shakespeare who wrote the sonnets or someone else with the same name," he said. "We know what vitamin D does, and there is a very plausible biological hypothesis for how it works. There might be something else that is having the effect, but why would we look for it when it is there under our noses? The amount of research on other supplements is nothing like as great as that on vitamin D."