Does vitamin D supplementation reduce mortality in healthy adults and adults in a stable phase of disease?
A major drawback in most of the included trials was the relatively large proportion (>8%) of participants who dropped out. There was a lack of information on the effect in men and in younger persons of both sexes. Due to the risk of attrition bias, outcome reporting bias and other biases, it is not yet possible to recommend or refute the use of vitamin D for reducing all-cause mortality or cancer mortality.
Numerous observational studies suggest that optimal vitamin D status may be associated with fewer occurrences of cancer and cardiovascular disease (such as heart attack or stroke). Vitamin D is synthesised in the skin as vitamin D3 (cholecalciferol) or is obtained from dietary sources or supplements as vitamin D3 or vitamin D2 (ergocalciferol).