Higher intakes of vitamin D could reduce the risk of certain cancers by as much as 50 per cent, suggests a new study, lending weight to calls for increased supplement intake and food fortification with the vitamin.
"The high prevalence of vitamin D deficiency, combined with the discovery of increased risks of certain types of cancer in those who are deficient, suggest that vitamin D deficiency may account for several thousand premature deaths from cancer annually," said the researchers from the University of California Moores Cancer Center.
Their conclusions are based on a study to be published in the February issue of The American Journal of Public Health (available online from 27 December 2005), which combined 63 observational studies of vitamin D status in relation to the risk of colon, breast, prostate or ovarian cancer.
The systematic review analyses data from the studies that were reported between January 1966 and December 2004, including 30 colon cancer studies, 13 breast cancer and seven for ovarian cancer.
While such systematic reviews are prone to errors, especially when drawing on old results and data gathering techniques, the authors are confident of their findings.
"A preponderance of evidence, from the best observational studies the medical world has to offer, gathered over 25 years, has led to the conclusion that public health action is needed," said co-author Cedric Garland.
The researchers recommend a daily intake of vitamin D of 1000 international units (IU), half the upper safe intake limit recommended in the EU and the US.
Vitamin D is made by the body on exposure to sunshine, or can be consumed in small amounts in milk, fish, liver and egg yolk. However because of the low amounts present in the diet, and lack of sunshine in northern climates, some estimates claim that at least 60 per cent of the UK population is vitamin D deficient.
Previous research has found that vitamin D deficiency is also higher in the northeastern United States where sunshine levels are weaker. Incidence of deficiency is greater in African Americans whose increased skin colouring reduces their ability to make the vitamin.
"Many people are deficient in vitamin D. The easiest and most reliable way of getting the appropriate amount is from food and a daily supplement," said Garland.
The researchers see increasing the public's consumption of supplements and fortified foods as an inexpensive tool for the prevention of diseases that claim millions of lives every year. There are over 2.5 million new cases worldwide of the cancers mentioned annually.
In a statement on 30 December, the UK's number two health and beauty retailer Superdrug said that it had seen a 100 per cent increase in sales of supplements containing vitamin D in the two days following the media's reports about the new study.
It remains to be seen whether this boost to sales is sustained.