Polymorphisms in the Vitamin D System and Health, 2013

Vitamin D is produced in the skin after sun exposure or obtained from food, mainly fatty fish or vitamin D supplements. For activation vitamin D must be hydroxylated in the liver to 25(OH)D and thereafter in the kidney to 1,25(OH)2D. For 1,25(OH)2D to exert its effect it has to bind to the vitamin D receptor (VDR). The serum level of 25(OH)D is in part genetically determined and several polymorphisms with effects on serum 25(OH)D have been identified. These polymorphisms appear as important for the serum 25(OH)D level as the effect of season, or vitamin D supplementation. Vitamin D is not only vital for the skeleton, but appears also to be related to heart disease, diabetes, cancer and mortality. However, as the serum level of 25(OH)D is strongly influenced by lifestyle factors that are also related to health outcomes, it is difficult to decide whether the relation between vitamin D and health is causal or not. On the other hand, the polymorphisms are not influenced by life-style, and the effect of the polymorphisms will be life-long. Accordingly, they may be a better marker of vitamin D status than a single serum 25(OH)D measurement. Furthermore, there are a number of polymorphisms regarding the VDR that may be associated with health. In the Tromsø study DNA is available from almost 27,000 individuals, and end-point registers have been made for fractures, coronary infarction, diabetes, cancer and mortality. In the present study we therefore related the polymorphisms affecting the serum 25(OH)D level and the function of the VDR with these endpoints with the use of a case-cohort design. If we were to find the expected associations between the polymorphisms and diseases, this would further strengthen the role of vitamin D in human health, and may have importance for recommendations regarding vitamin D supplementation. Considering the high prevalence of vitamin D deficiency worldwide, this could potentially have huge consequences for public health.

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