Many studies over the last decade have suggested that supplementing the diet with vitamin D gives a variety of health benefits. Published research has suggested that vitamin D deficiency is associated with increased risk of all-cause and cardiovascular mortality (Dobnig H, et al. Arch Intern Med. 2008 Jun 23;168(12):1340).
But until now, there has been no consistent evidence documenting a beneficial effect on mortality from supplementation.
Cochrane Collaboration researchers conducted a systematic review of 50 randomized trials comparing vitamin D to placebo or no intervention. The trials included 94,148 study participants, with most studies comprised of women older than 70 years old. Vitamin D was given to participants for a median of two years.
Focusing on 32 of those trials involving nearly 75,000 patients, researchers found that one particular form of vitamin D, vitamin D3 (cholecalciferol), could significantly decrease all-cause mortality.
The relative risk [RR] was 0.94, 95%CI 0.91-0.98), with a number needed to treat (NNT) of 161 to prevent one death per year, assuming 10% mortality in controls (level 1 [likely reliable] evidence). Further subgroup analysis revealed that the observed risk-reduction was driven primarily by patients with insufficient levels of vitamin D at baseline.
In the Cochrane analysis, there were no significant differences in mortality with other forms of vitamin D, such as vitamin D2, alfacalcidol and calcitriol (level 2 [mid-level] evidence). Alfacalcidol and calcitriol tended to promote hypercalcaemia, and vitamin D3 with calcium significantly increased the risk of kidney stones. (Bjelakovic G, et al. Cochrane Database Syst Rev. 2011 Jul 6;(7):CD007470).
This article was adapted from the DynaMed Weekly Update. DynaMed, published by EBSCO Publishing, is a commercial-free clinical reference tool created by physicians for physicians and other health care professionals for use primarily at the 'point-of-care.' Offering clinically-organized summaries for more than 3,000 topics, DynaMed is updated daily and monitors an extensive collection of journals and evidence review sources. New evidence is integrated with existing content, and overall conclusions updated based on the best available evidence.