The protein thyroxine-binding globulin – or TBG (that moves thyroid hormones around the body) has long been an object of interest for researchers when examining the Indigenous community. Research completed in the 1980s identified that the levels of this protein found in Aboriginal Australians were lower than Caucasian levels. This caused researchers to call for Indigenous Australians diagnosed with Hypothyroidism to be re-tested, as the differences in TBG were thought to increase the amount of false-positive results.
Recent research has shown that these differences may in fact have wider environmental adaptations, as Indigenous Australians have also been found to have a genetic mutation that makes their TBG (and by extension, their metabolism) better able to adapt and respond to higher temperatures common to the harsh Australian climate.
Humans’ response to high temperatures
When humans get a fever (>39°C) the amount of the thyroid hormone thyroxine in the bloodstream begins to increase as TBG loses its ability to bind to it. At a body temperature of just 39°C, this increases the concentration of thyroxine in the bloodstream by 23% and temporarily moves the individual into an overactive thyroid (or Hyperthyroid) state.
This is not the case for Aboriginal Australians, who due to a genetic adaptation are able to retain the binding ability of TBG at higher temperatures, which releases less thyroxine into their system. Reducing the observed 23% increase in thyroxine to 10% in Indigenous Australians. Thus providing a lower comparative metabolic rate.
An environmental advantage?
The increased release of thyroxine and increased metabolism caused by the fever would normally be an advantage as it would assist the body to fight the infection. However, in the hotter climate of central Australia, where temperatures can increase to 45°C or more, this increased metabolism would then become a risk. At these temperatures, Indigenous Australians would be dealing with dehydration and heat exhaustion, which would be hindered by an increased metabolic rate.
The focus for Indigenous Australians in the healthcare space is quite often on closing the gap of disadvantage. However, as this week is NAIDOC, it’s an opportunity for all Australians to learn about our First Nations people and celebrate their wins. So we wanted to take the opportunity to do something different and celebrate this environmental advantage that has been developed by Indigenous Australians in response to living in the harsh Australian climate and enabled them to survive and function at extreme temperatures.
Dick, M. & Watson, F. (1980). Prevalent low serum thyroxine-binding globulin level in Western Australian aborigines: it’s effect on thyroid function tests. Medical Journal of Australia, 1(3), 115-118.
Qi, X., Chan, W. L., Read, R. R., Zhou, A., & Carrell, R. W. (2014). Temperature-responsive release of thyroxine and its environmental adaptation in Australians. Proceedings of the Royal Society of Biological Sciences, 281(1779). https://doi.org/10.1098/rspb.2013.2747
Watson, F., Dick, M., & Khin, D. T. (1983). Laboratory evaluation of thyroid function in Australian aborigines. Medical Journal of Australia, 1(2), 66-69.