We evolved to match local micronutrient levels, which may be a problem

The historical availability of zinc and other trace minerals in human diets has largely been dictated by local soil conditions. Recent research reveals that as early human populations migrated globally, they adapted to local disparities in micronutrient levels.

This adaptation may carry certain unintended consequences. For instance, it has been proposed that the smaller stature seen in some populations is a result of adaptation to low iodine availability. Furthermore, these ancient modifications may result in contemporary individuals experiencing an inappropriate balance of micronutrient intake.

“For the majority of human history, the micronutrient make-up of diets was intrinsically linked to local geochemical factors,” states Jasmin Rees from the University of Pennsylvania.

In her groundbreaking research, the team studied nearly 900 genomes globally to uncover signs of adaptation in relation to 13 trace elements, including iron, manganese, and selenium. The researchers specifically searched for positive selection indicators in 270 genes connected to the absorption of these elements, aiming to identify genetic variations that have proliferated due to their associated benefits.

The most compelling evidence emerged from analysis of genes related to iodine in the Maya populations. Similar genetic markers were also identified in the Mbuti and Biaka communities in Central Africa, populations noted for their shorter stature relative to others.

Previous studies have suggested that the shorter physical height of the Mbuti and Biaka could be attributed to adaptations to lower iodine levels, as these iodine-associated genes have implications on thyroid hormone regulation, directly influencing growth metrics. Interestingly, these groups also experience lower instances of goitre, a condition that signifies iodine deficiency.

Notably, Rees points out that the Maya community also exhibits shorter average heights, supporting the hypothesis that low iodine adaptation could impact growth. Rainforest soil, commonly low in iodine, aligns with this perspective.

“We acknowledge the speculative nature of these findings,” she mentions. “While we cannot definitively state the cause of these growth patterns, our observations reveal intriguing correlations between iodine gene selection and shorter populations.”

In populations such as the Uyghurs and Brahui of Central and South Asia, where there are elevated levels of soil magnesium, researchers noted significant selection pressures on genes linked to magnesium absorption. Certain variants that are associated with reduced magnesium uptake have been observed, possibly as protective mechanisms against potential toxicity linked to environmental abundance.

This represents merely a fraction of the broader findings—evidence of positive genetic selection for micronutrient adaptation was observed universally across various global populations. “We are seeing extensive indications of adaptation in these genetic markers,” asserts Rees.

This study marks a new frontier, with further investigations required to clarify the implications of numerous gene variations identified. In our globally traded food market, future research might reveal that certain populations require varying levels of specific micronutrients compared to what they currently consume. Rees draws a parallel to guidelines in countries like the UK, where individuals with darker skin are advised to take vitamin D supplements year-round rather than only in winter.

“Understanding whether specific populations necessitate extra micronutrient supplementation could be vital for public health planning,” mentions Mark Stoneking from the Max Planck Institute for Evolutionary Anthropology in Germany.

“Their research exemplifies top-tier work in identifying selection signatures within genomic data,” he adds, emphasizing, however, that further verification is required to ascertain which signatures are truly indicative of selective pressures, as some may likely turn out to be misleading.