Vitamin D may protect against prostate cancer
as likely to develop aggressive forms of prostate cancer as those
with lower amounts, reported researchers last week.
"Our findings suggest that vitamin D plays an important protective role against prostate cancer, especially clinically aggressive disease," said lead investigator Dr Haojie Li, a research fellow at Brigham and Women's Hospital and Harvard University School of Public Health.
Prostate cancer is the second most common cancer in men after lung cancer. It was the most common form of cancer diagnosed among men in the European Union during 2004, representing 15 per cent of male cancers and 238,000 new cases, according to figures released last week by the International Agency for Research on Cancer (IARC).
The research, presented at the 2005 Multidisciplinary Prostate Cancer Symposium in the US, is the first to demonstrate a link between the vitamin and prevention of prostate cancer.
Previous studies have found an association with this vitamin and other cancers such as breast and colon. Vitamin D is being increasingly studied for its cancer protective action, following findings that cancer death rates are lower in countries with sunnier climates. The body requires sunlight to manufacture vitamin D.
Vitamin D levels are also lower in older men, who are most prone to prostate cancer.
In addition, blacks, who have a lot of melanin in their skin, which blocks the ultraviolet light needed for vitamin D production, also have the highest rates of prostate cancer.
Using blood samples taken from the participants in the Physician's Health Study, investigators compared prediagnostic plasma levels of two vitamin D metabolites between 1,029 men who subsequently developed prostate cancer and 1,371 healthy individuals matched for age and smoking status.
They also examined the associations between two polymorphisms (BsmI or FokI) in the vitamin D receptor (VDR) gene and the risk of prostate cancer, as well as whether the associations between vitamin D metabolites and prostate cancer risk vary according to VDR genotype.
Men with blood plasma levels of both 25-hydroxyvitamin D (25 D) and 1,25 dihydroxyvitamin D (1,25 D) above the median had a 45 per cent lower risk of developing aggressive prostate cancer during 13 years of follow-up.
Individually, prediagnostic plasma levels of either type of vitamin D alone or polymorphisms of the BsmI or FokI gene did not influence prostate cancer risk.
Furthermore, among men with a specific genotype called homozygous FokI FF, those with high levels of both 25 D and 1,25 D had a 55 per cent lower risk of prostate cancer and a 77 per cent decrease in the risk of aggressive prostate cancer.
"This research underscores the importance of obtaining adequate vitamin D through skin exposure to sunlight or through diet, including food and supplements," added Dr Li.
Supplements and fortified foods are seen as an effective way of improving levels of the vitamin without putting skin at risk through increased exposure to sun.
"With the big debate about sunlight and cancer, you need to look to the diet. Fortification, if done sensibly, is the only way to achieve optimum vitamin D levels," Sue Fairweather-Tait, head of nutrition at the UK's Institute of Food Research told NutraIngredients.com last year.
"The best source of vitamin D at the moment is fortified cereals," she said.
Another study presented at the conference found that overweight and obese men are more likely to be diagnosed with advanced prostate cancer and die of the disease than men who are of a normal weight.
Being obese may delay the diagnosis of prostate cancer and could also be associated with a biologically more aggressive form of prostate cancer, said the researchers.
