Vitamin D, immune function, and atherosclerosis. Where are we now?

The role of vitamin D in regulating calcium metabolism and skeletal growth and disease is widely recognized. Indeed, current recommendations for serum vitamin D concentrations are based on these parameters. A serum vitamin D <20 ng/mL is considered deficient, concentrations between 20 and 30 ng/mL are insufficient, and >30 ng/mL is adequate. However, over the past number of years, epidemiological studies, randomized clinical trials, and preclinical animal and cell culture-based research have demonstrated that vitamin D modulates immune function. Cardiovascular disease (CVD), the leading cause of morbidity and mortality in the United States and in industrialized nations, is mediated in part by chronic inflammation as well as by other well-established risk factors including dyslipidemia, hypertension, obesity, and diabetes. Vitamin D deficiency (<20 ng/mL or <50 nM) is associated with increased CVD risk. As described in this review, several recent systematic reviews and meta-analyses provide some evidence that vitamin D administration to individuals with vitamin D deficiency may have little effect on CVD-related mortality. Many well-designed randomized clinical trials in the general population as well as in people at risk for CVD-related complication later in life provide evidence that treatment may be beneficial. These latter studies as well as the paucity of information regarding the optimal vitamin D concentration required for optimizing immune function in patients indicate that more research is needed to address whether vitamin D supplements may be a cost-effective intervention for preventing CVD.