We’ve Adapted to Local Micronutrient Levels, but This Could Lead to Issues

Historically, the quantity of zinc and other trace elements in human nutrition was largely influenced by the local soil conditions. Recent findings suggest that our ancestors adapted to varying levels of micronutrients as they dispersed globally.

This adaptation may have resulted in notable repercussions. For instance, the shorter statures observed in certain populations might be a consequence of adapting to low iodine availability. Additionally, these historical adjustments may lead to some individuals today experiencing deficiencies or excesses of specific micronutrients.

“For much of human history, the micronutrient profile of our diet has been determined by the soil beneath us,” stated Jasmine Reese from the University of Pennsylvania.

Reese and her team analyzed the genomes of nearly 900 individuals globally to uncover evidence of adaptation to local concentrations of 13 trace elements, including iron, manganese, and selenium. They investigated signs of positive selection in 270 genes related to the ingestion of these elements, highlighting benefits of genetic variations that became more common within certain populations.

The most compelling evidence was for iodine-related genes in the Maya populations of Central America. A similar pattern was observed in the Mbuti and Biaka peoples of Central Africa.

In 2009, it was suggested that the short stature of the Mbuti and Biaka peoples may be attributed to their adaptation to low iodine levels. This relates to iodine-binding genes that influence thyroid hormone function and subsequently growth. These groups are also notably more susceptible to thyroid enlargement due to dietary iodine deficiencies compared to nearby populations.

Maya individuals also exhibit notably shorter statures, providing supporting evidence for the hypothesis that adaptations to low iodine levels influence height. Moreover, it is emphasized that the soils in the Mayan regions, particularly rainforests, are recognized as low in iodine.

“This is quite speculative,” she notes. “While I can’t definitively link short stature directly to iodine levels, we observe a striking correlation with the selection of iodine-related genes in these shorter populations.”

In the Uighur and Blahui populations of Central and South Asia, where soil magnesium concentrations are particularly elevated, there is strong selection impacting two genes involved in magnesium uptake. Some gene variants correlated with low magnesium levels suggest adaptive changes that minimize magnesium absorption to avoid toxicity from environmental excess.

These instances are merely a couple of examples. The research team has identified signs of positive selection related to at least one micronutrient across virtually all examined populations worldwide. “We truly observe a widespread signature of adaptation,” Reese states.

This research marks just the beginning, she emphasizes. Further investigations are crucial to elucidate the impacts of the numerous genetic variants discovered by the team. Given the global trade in food, individuals within certain populations may require increased or decreased intake of specific micronutrients. Reese compares this to populations in the UK, where individuals with darker skin may need vitamin D supplementation not just in winter but throughout the entire year.

“Understanding whether a specific population may require certain micronutrient supplements is essential,” notes Mark Stoneking at the Max Planck Institute for Evolutionary Anthropology in Germany.

“They’ve conducted groundbreaking work in identifying signatures of selection from genomic data,” he states. “However, further research is needed to confirm these findings as genuine cases of selection, as some may inevitably turn out to be false positives.”