Past studies have suggested that deficiencies in vitamin D might be associated with a higher risk of death from cancer, heart disease and diabetesillnesses that account for 60 percent to 70 percent of deaths in high-income nations, according to background information in the article.
"If the associations made between vitamin D and these conditions were consistent, then interventions effectively strengthening vitamin D status should result in reduced total mortality," the authors write.
Philippe Autier, M.D., of the International Agency for Research on Cancer, Lyon, France, and Sara Gandini, Ph.D., of the European Institute of Oncology, Milano, Italy, searched for randomized controlled trials of vitamin D supplements published before November 2006. They analyzed 18 separate trials that included 57,311 participants and evaluated doses of vitamin D ranging from 300 to 2,000 international units, with an average dose of 528 international units. Most commercially available supplements contain between 400 and 600 international units.
Over an average follow-up period of 5.7 years, 4,777 of the participants died. Individuals who took vitamin D had a 7 percent lower risk of death than those who did not. In the nine trials that collected blood samples, those who took supplements had an average 1.4- to 5.2-fold higher blood level of vitamin D than those who did not.
"Mechanisms by which vitamin D supplementation would decrease all-cause mortality are not clear," the authors write. Vitamin D could inhibit some mechanisms by which cancer cells proliferate, or it may boost the function of blood vessels or the immune system, they note.
"In conclusion, the intake of ordinary doses of vitamin D supplements seems to be associated with decreases in total mortality rates," the authors write. "The relationship between baseline vitamin D status, dose of vitamin D supplements and total mortality rates remains to be investigated.
Population-based, placebo-controlled randomized trials in people 50 years or older for at least six years with total mortality as the main end point should be organized to confirm these findings."