Trials included in the review assessed

For the second study, researchers led by the University of Cambridge in the UK and the Erasmus Medical Centre in the Netherlands analyzed observational cohorts and randomized controlled trials that looked at the association between vitamin D and death from cardiovascular disease and cancer, among other conditions.

Trials included in the review assessed the effects of both naturally occurring vitamin D and vitamin D2 and D3 supplements.

In the randomized controlled trials, follow-up varied from 3 to 7 years. The research team found that of the individuals who took vitamin D supplements, 2,527 deaths occurred, compared with 2,587 deaths in control groups.

Looking at the results in more detail, the researchers found that when vitamin D2 supplements were taken alone, there was no reduction in participants' risk of death.

But when vitamin D3 supplements were taken alone, participants had an 11% reduction in the risk of death.

However, the research team notes that since the trials in this review involved elderly populations, in which death is commonly a result of coexisting conditions, further research is warranted to determine the correct dosage of vitamin D supplements that should be taken, duration and safety of the supplements, and whether vitamin D2 or D3 pose different effects on the risk of mortality.

'We should stick to what is proven'

Commenting on the take home messages of both studies, Sattar and Welsh say:

"Firstly, health care professionals should treat all observational data cautiously, as existing disease and associated risk factors may cause, rather than be a consequence of, low circulating 25-hydroxyvitamin D.

Secondly, before widespread supplementation can be considered, new trial data are needed with a focus on potential risks as well as benefits."

Until concrete evidence on the heath benefits of vitamin D is provided, Sattar and Welsh say doctors should avoid recommending the use of vitamin D supplements for patients who do not have bone disease related conditions.

They conclude:
"To improve health and prevent chronic disease, we should stick to what is proven; encourage better lifestyles in general and target established risk factors in people at elevated risk."