Genetic adaptation to levels of dietary selenium in recent human history.

As humans migrated around the world, they came to inhabit environments that differ widely in the soil levels of certain micronutrients, including selenium (Se). Coupled with cultural variation in dietary practices, these migrations have led to a wide range of Se intake levels in populations around the world. Both excess and deficiency of Se in the diet can have adverse health consequences in humans, with severe Se deficiency resulting in diseases of the bone and heart. Se is required by humans mainly due to its function in selenoproteins, which contain the amino acid selenocysteine as one of their constituent residues. To understand the evolution of the use of this micronutrient in humans, we surveyed the patterns of polymorphism in all selenoprotein genes and genes involved in their regulation in 50 human populations. We find that single nucleotide polymorphisms from populations in Asia, particularly in populations living in the extreme Se-deficient regions of China, have experienced concerted shifts in their allele frequencies. Such differentiation in allele frequencies across genes is not observed in other regions of the world and is not expected under neutral evolution, being better explained by the action of recent positive selection. Thus, recent changes in the use and regulation of Se may harbor the genetic adaptations that helped humans inhabit environments that do not provide adequate levels of Se in the diet.