Adequate supplies of certain nutrients and vitamins have been linked to the prevention of different diseases. As a result, supplementation with vitamins has become a popular tool for those seeking optimal health. While vitamins are important to bodily function, it is not always clear how beneficial supplementation is in the average person. In some studies, Vitamin D has been associated with reduced cancer risk. It has also been shown to decrease the risk of falls in elderly patients. There have been conflicting reports on its effect on mortality.
Researchers examined several past studies to determine benefits and harms of vitamin D supplementation. The study, published in the Cochrane database, found that vitamin D3 supplementation may decrease the risk of dying in elderly women. However, they also found that there may be an increased risk of renal stone formations when D3 was combined with calcium.
About the Study
The study was a systematic review of 50 randomized trials that assessed benefits or adverse events of vitamin D supplementation in a total of 94,148 participants. Most of the participants were women over 70 years of age who lived in institutions and required assisted care. The dose and duration of vitamin D varied between studies but the average duration was two years. The supplements included vitamin D3 (cholecalciferol), vitamin D2 (ergocalciferol), or an active form of vitamin D which were compared to placebo or no treatment.
Only vitamin D3 was associated with decrease mortality rates during trial duration. In 32 trials with 74,789 participants there was a 6% decrease in mortality with D3 supplementation.
Some adverse events were noted with specific types of vitamin D. Active forms of vitamin D (alfacalcidol and calcitriol) were associated with hypercalcemia (high calcium levels in blood) in three trials. Vitamin D3 that was combined with calcium was associated with a 17% increased risk of nephrolithiasis (kidney stones) in analysis of four trials.
How Does This Affect You?
A systematic review combines several smaller studies with sometimes conflicting results to provide clearer, more concise outcomes. In this case, the review demonstrated that a particular type of vitamin D supplementation was associated with decreased mortality, but it did not demonstrate what may have led to this decrease (such as protection against cancer or heart disease). The study was also limited by the population, which means the benefits may only be seen in older women currently living in institutions.
Although some vitamin D does come from diet, the majority comes from exposure to sunlight. This exposure can be limited by lack of outdoor time, sunscreen use, and living in areas with decreased sun exposure (northern areas in winter). Supplementation with vitamin D3 may be beneficial for people with low vitamin D levels or those with limited sun exposure, such as residents of an institution.
American Dietetic Association
United States Department of Agriculture Dietary Guidelines
Bjelakovic G, Gluud LL, Nikolova D, et al.
Vitamin D supplementation for prevention of mortality in adults.
Cochrane Database Syst Rev. 2011 Jul 6;(7):CD007470.