Up until now there has been no clear view on whether there is a real benefit of taking vitamin D. "A Cochrane meta-analysis published only a couple of years ago found that there was some evidence for benefit, but it could not find an effect on mortality. We were, however, aware that more trials had been published and wanted to assess the effects of vitamin D when you added all the data together," said Dr Goran Bjelakovic, who works at Department of Internal Medicine -- Gastroenterology and Hepatology, at the University of Nis, in Serbia and at The Cochrane Hepato-Biliary Group at The Copenhagen Trial Unit in Copenhagen, Denmark.

The eight-strong international team of researchers identified 50 randomised trials that together had 94,148 participants. They had a mean age of 74 years, and 79% were women. "Our analyses suggest that vitamin D3 reduces mortality by about 6%. This means that you need to give about 200 people vitamin D3 for around two years to save one additional life," says Bjelakovic.

There were no significant benefits of taking other forms of vitamin D such as vitamin D2, and the active forms of the vitamin, alfacalcidol or calcitriol. However, the researchers point out that they could only find much less data relating to these types of vitamin D and so these conclusions should be taken with caution. "We need to have more randomised trials that look specifically to see whether these forms of vitamin D do or don't have benefits," says Bjelakovic. His team did conclude that alfacalcidol and calcitriol significantly increased the risk of hypercalcaemia, and vitamin D3 combined with calcium significantly increased the risk of kidney stones.

There have been reports and comments that taking vitamin D can reduce the risk of getting cancer, but this work showed no evidence that vitamin D reduced cancer-related mortality.

"Previous reviews of preventive trials of vitamin D have not included as much information and have not examined the separate influence of different forms of vitamin D on mortality. By taking data from a larger number of trials we have been able to shed much more light on this important issue," says Bjelakovic.

Note: If no author is given, the source is cited instead.

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