Although nearly half of adults in the United States currently take vitamin D in hopes of improving their overall health, new research suggests that adding these supplements to our dietary intake has no effect on heart attack, stroke, cancer, and overall mortality risk. A study out of the University of Auckland in New Zealand revealed that vitamin D supplementation may hold no healthy benefit and could even be considered harmful, which begs the question: What is vitamin D good for?

“Our findings suggest that vitamin D supplementation with or without calcium does not reduce skeletal or non-skeletal outcomes in unselected community-dwelling individuals by more than 15 percent,” the authors of the study concluded. “Future trials with similar designs are unlikely to alter these conclusions.”

According to the National Institutes of Health’s Office of Dietary Supplements, nutrients in vitamin D can help maintain healthy bones by aiding the body in calcium absorption. Not only do vitamin D supplements help strengthen our bones, but a majority of health care professionals say its benefits also include anti-inflammatory properties, cell proliferation, and healthy immune function.

The NIH recommends anyone between the ages of 1 and 70, including pregnant and breastfeeding women, should take in no less than 600 international units (IU) each day. Only certain types of food contain vitamin D including fortified milk, salmon, tuna, egg yolks, and mushrooms. Our bodies produce vitamin D when our skin is directly exposed to the sun’s rays.

Lead researcher of this study Dr. Mark Bolland and his colleagues from the university combed through data from 40 randomized controlled trials based on vitamin D supplementation. The research team used a cross section of meta-analyses, including “futility analysis,” which is meant to dissuade any future research that may contradict existing evidence. Recent studies suggest that low levels of vitamin D are a consequence of poor health rather than a cause.

Findings from the researchers’ comprehensive analysis revealed that vitamin D’s effect on heart attack, stroke, cancer, and total fracture, with or without calcium, lies well below a “futility threshold.” The research team failed to prove that vitamin D can improve our overall health by over 15 percent. In fact, Bolland noted that vitamin D supplements increased a patient’s risk of suffering a hip fracture. Vitamin D’s ability to reduce our risk of mortality by at least five percent was inconclusive.

"Without stringent indications — i.e. supplementing those without true vitamin D insufficiency — there is a legitimate fear that vitamin D supplementation might actually cause net harm," said Professor Karl Michaëlsson, from Uppsala University in Sweden, commenting on the study.

Source: Grey A, Gamble G, Reid I, Bolland M. The effect of vitamin D supplementation on skeletal, vascular, or cancer outcomes: a trial sequential meta-analysis. The Lancet Diabetes & Endocrinology. 2014.