Vitamin D and evolution: Pharmacologic implications.

Vitamin D is produced non-enzymatically when the cholesterol precursor 7-dehydrocholesterol is exposed to UV-B, i.e., evolutionary the first function of the molecule was that of an UV-B radiation scavenging end product. Vitamin D endocrinology started when some 550 million years ago first species developed a vitamin D receptor (VDR) that binds with high affinity the vitamin D metabolite 1α,25-dihydroxyvitamin D. VDR evolved from a subfamily of nuclear receptors sensing the levels of cholesterol derivatives, such as bile acids, and controlling metabolic genes supporting cellular processes, such as innate and adaptive immunity. During vertebrate evolution, the skeletal and adaptive immune system showed in part interesting synchronous development although adaptive immunity is evolutionary older. There are bidirectional osteoimmune interactions between the immune system and bone metabolism, the regulation of both is under control of vitamin D. This diversity of physiological functions explains the pleiotropy of vitamin D signaling and opens the potential for various pharmacological applications of vitamin D as well as of its natural and synthetic derivatives. The overall impact of vitamin D on human health is demonstrated by the fact that the need for its efficient synthesis served in European hunter and gatherers as an evolutionary driver for increased 7-dehydrocholesterol levels, while light skin was established far later via populations from Anatolia and the northern Caucasus entering Europe 9000 and 5000 years ago, respectively. The later population settled preferentially in northern Europe and we hypothesize that that the introduction of high vitamin D responsiveness was an essential trait for surviving dark winters without suffering from the detrimental consequences of vitamin D deficiency.