High intake of the vitamin has previously been linked to a lower risk of prostate cancer, while other studies have indicated that vit D can suppress the spread of the cancer. This is the first study that claims to have identified a specific mechanism.
Over half a million news cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths. More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years.
The in vitro study, reported in the journal Carcinogenesis (Vol. 27, pp. 32-42), showed that vitamin D, in the form of the highly active 1alpha, 25-dihydroxyvitamin D3 (1,25-VD), inhibited the function of protease enzymes that are involved in tumour invasion.
"We found that 1,25-VD decreased matric metalloproteinases (MMP-9) and cathepsins (CPs), while it [also] increased the activity of their counterparts, tissue inhibitors of metalloproteinase-1 (TIMP-1) and cathepsin inhibitors," wrote lead author Bo-Ying Bao from the University of Rochester and Taipei Medical University.
"Mechanistic studies showed that 1,25-VD did not suppress MMP-9 expression at the transcriptional level, but reduced its mRNA stability," said Bao.
The body of evidence for the benefits of vitamin D against prostate cancer is rapidly growing, but the scientists do not recommend taking high doses of the vitamin warning against increased calcium blood levels and kidney problems.
The current RDI of 400 International Units (IU) was recently challenged by researchers, with some calling for an RDI of 1000 IU, while others recommend 2000 IU, equal to the so-called upper safe limit.
"The best way to get vitamin D is to drink milk, get modest exposure to the sun, and take a vitamin pill to enrich vitamin D, which might prevent cancer," said lead researcher Yi-Fen Lee.
The joint US-Taiwan team will now turns its attention to enhancing the effects of vitamin D with other vitamins, like vitamin E, without increasing toxicity.
The study is yet more music to the ears of supplement makers, coming a week after scientists reported that diet and supplements, and not sunshine, should be the source of people's vitamin. Vitamin D sales have rocketed in the UK with some retailers reporting 400 per cent increases in supplement sales.