As an endocrine fellow, I see the consequences of low vitamin D levels on bone health. In osteoporosis clinics, I regularly review patients’ vitamin D levels and prescribe vitamin D supplements in all forms — tablets, capsules, and oils. Patients often ask, “Is vitamin D potentially useful for anything else?” Providing an evidence-based answer to this question has been difficult.
In the past decade, there has been growing interest in the question of whether vitamin D supplementation could reduce the risk of developing diseases beyond bone-related disorders. Driven by results of earlier studies, particular interest has emerged in a possible relation between vitamin D and risk for two leading causes of death in the U.S. — cardiovascular disease and cancer. Vitamin D is a dietary supplement that is easy to administer, largely affordable, and not generally associated with harm. Therefore, the answer to the question of whether vitamin D supplementation reduces the risk of these two diseases has been highly anticipated.
Results of the Vitamin D and Omega-3 Trial (VITAL), published online first in NEJM, provides the answer. This large U.S. primary prevention trial examined whether two supplements lower the incidence of cardiovascular disease or cancer in nearly 26,000 adults with no history of cardiovascular disease, cancer, or other serious disorders. In the vitamin D arm of the study, participants were randomized to receive vitamin D3 (2000 IU/day) or placebo and followed for a median of 5.3 years.
Despite an increase in mean serum 25-hydroxyvitamin D level with vitamin D3 supplementation, researchers found no significant differences between the vitamin D and placebo groups in the incidence of the primary endpoints of major adverse cardiovascular events (myocardial infarction, stroke, or cardiovascular-related death) or invasive cancer. In a summary of VITAL in NEJM Journal Watch, Editor-in-Chief, Allan Brett, MD comments, “The VITAL trial should dampen enthusiasm for routine vitamin D screening and routine supplementation. Observational studies suggest adverse health outcomes in people with low vitamin D levels, but such studies are plagued by confounding and reverse causality (e.g., less healthy people are more likely to have minimal sun exposure and poor nutritional status).”
From my perspective as an endocrine fellow, VITAL has made my job in clinic a bit easier. Now, at least to the best of our current knowledge, I can tell patients that the evidence indicates that vitamin D supplementation is not useful for the primary prevention of cardiovascular disease or cancer.
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Angela is a 2018-2019 NEJM editorial fellow. She is an endocrine fellow who trained at Flinders Medical Centre and the Royal Adelaide Hospital. Angela recieved her medical degree from the University of Adelaide, and masters of public health from the University of Sydney. Her clinical and research interests are in the areas of glucocorticoid and cardiovascular endocrinology and diabetes medicine.