The high worldwide prevalence of
vitamin D deficiency is largely the result of low sunlight exposure with subsequently limited cutaneous
vitamin D production. Classic manifestations of
vitamin D deficiency are linked to disturbances in bone and
mineral metabolism, but the identification of the
vitamin D receptor in almost every human cell suggests a broader role of
vitamin D for overall and cardiovascular health. The various cardiovascular protective actions of
vitamin D such as anti-diabetic and
anti-hypertensive effects including
renin suppression as well as protection against
atherosclerosis and
heart diseases are well defined in previous experimental studies. In line with this, large epidemiological studies have highlighted
vitamin D deficiency as a marker of cardiovascular risk. However, randomized controlled trials (RCTs) on
vitamin D have largely failed to show its beneficial effects on
cardiovascular diseases and its conventional risk factors. While most prior
vitamin D RCTs were not designed to assess cardiovascular outcomes, some large RCTs have been initiated to evaluate the efficacy of
vitamin D supplementation on cardiovascular events in the general population. When considering the history of previous disappointing
vitamin RCTs in general populations, more emphasis should be placed on RCTs among severely
vitamin D-deficient populations who would most likely benefit from
vitamin D treatment. At present,
vitamin D deficiency can only be considered a cardiovascular risk marker, as
vitamin D supplementation with doses recommended for
osteoporosis treatment is neither proven to be beneficial nor harmful in
cardiovascular diseases.