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Vitamin D: A magic bullet or a myth?

Reijven, P.L.M., Soeters, P.B.
Clinical nutrition 2019
autoimmune diseases, binding proteins, bone health, coronary disease, disease severity, epidemiological studies, foods, human health, inflammation, metabolism, mortality, neoplasms, observational studies, receptors, sepsis (infection), systematic review, vitamin D, vitamin status
The interest in Vitamin D (Vit D) is increased after the finding of Vit D receptors in many different cells. This led to the hypothesis that Vit D may have more impact on human health than its role in bone health. Epidemiological studies found associations between low plasma levels of Vit D and the prevalence of many diseases. However, Large RCTs did not find convincing evidence for a positive effect of Vit D supplementation on cancer, cardiovascular disease, auto-immune disease and inflammatory diseases. In this review, the results are described of a literature search regarding the relationship between Vit D status and different diseases.Pubmed was used to find systematic reviews of observational studies describing the association between Vit D status, diseases (cancer, coronary heart diseases, auto-immune diseases, sepsis) and mortality. Subsequently, a search was performed for RCTs and the results of large RCTs are described. Studies with a positive intervention effect on primary or secondary outcome variables are summarized. No exclusion criteria were used.The metabolism of Vit D is reviewed, its endogenous production and the intake from food, its activation and transport in the body. The article addresses the effects of diseases on the metabolism of Vit D with special focus on the role of Vit D Binding Protein and its effects on assessing Vit D status. Studies addressing the association between vitamin D status and cancer, cardiovascular diseases, auto-immune diseases, inflammation and severe illness are reviewed. A search for RCTs with positive effects of Vit D supplementation on different diseases yielded only a few studies. The vast majority of RCTs showed no significant positive effects. The presumed high prevalence of Vit D deficiency is questioned based on these results and on altered concentrations of Vit D binding protein, leading to low Vit D levels in plasma but not to low active Vit D levels during disease related inflammation In these conditions, plasma levels of Vit D are therefore not a valid reflection of Vit D status. Reversed causality is described as a possible factor interfering with the correct assessment of the Vit D status. It is concluded that further widespread fortification of foods and stimulation of supplement use should be reconsidered.