The new review, published in the Archives of Internal Medicine, comes at a time when vitamin D is a hot topic linked to benefits including lower risk of some cancers and fewer falls for elders.
The body makes vitamin D when exposed to sunshine. Vitamin D is also found in some foods, including salmon, and in some fortified foods, including some dairy products and cereals.
But some experts are concerned that vitamin D deficiency is too common and suggest that the current recommended intake of vitamin D is too low.
The new vitamin D review comes from Philippe Autier, MD, and Sara Gandini, PhD.
Autier works for the International Agency of Research on Cancer in Lyon, France. Gandini works for the European Institute of Oncology in Milan, Italy.
Together, they analyzed the results of 18 vitamin D studies that included mortality rates.
More than 57,000 adults in the U.S., U.K., and Europe participated in the studies. Most of them were "frail" elders with low blood levels of vitamin D, write Autier and Gandini.
Their daily vitamin D doses ranged from 300 to 2,000 international units (IU), averaging 528 IU per day, in the form of ergocalciferol (vitamin D-2) or cholecalciferol (vitamin D-3).
Each study was designed differently, but on average, participants were followed for 5.7 years. During that time, 4,777 participants died of any cause.
People taking vitamin D were 7% less likely to die during the studies. The precise reason for their lower death rate isn't clear, and the reviewers aren't recommending a specific vitamin D dose.
An editorial published with the study recommends more research on vitamin D's benefits.
"The roles of moderate sun exposure, food fortification with vitamin D, and higher-dose vitamin D supplements for adults need to be debated," writes editorialist Edward Giovannucci, MD, ScD, who works in Harvard School of Public Health's nutrition department