Over the past ten years, more than 30,000 manuscripts have been published worldwide, demonstrating a variety of health benefits of vitamin D [1]. Meanwhile, a relatively smaller number of publications reported insufficient evidence of extra-skeletal biological effects of vitamin D in humans [2]. For example, Autier et al. [3] and Bolland et al. [4] published review articles suggesting that hypovitaminosis D is an epiphenomenon that coincides with
poor health outcomes [3], and that the correction of vitamin D deficiency has no beneficial effects [3]. They also claim that conducting randomized controlled trials (RCTs) searching for vitamin D-dependent health outcomes is futile [4], but their metaanalyses were far from satisfactory because of the bias of selection of studies.

In contrast, other reviews, original studies, and meta-analyses strongly pointed towards vitamin D as having significant beneficial effects and an important micronutrient component in the prevention of diseases [5–10]. In fact, is it not surprising, when general practitioners (GPs) review scientific papers showing effects of vitamin D on reducing the risks of cardiovascular
disease, stroke, heart failure, cancer, diabetes, autoimmune diseases, infections, secondary to having year-around, higher 25- hydroxy vitamin D [25(OH)D] serum concentrations, they may be confused as to what to believe and are thus, skeptical.