When the Cold Gets under Your Skin: The Variation and Metabolic Effects of Brown Adipose Tissue Activity in Samoans

This dissertation inferred brown adipose tissue (BAT) activity and its metabolic effects in Samoans. I assessed the changes in metabolic rate and body heat dissipation associated with BAT activity as a result of mild cold exposure. I also measured fasting glucose, cholesterol levels, and substrate metabolism by BAT, granting insight into the potential health benefits of BAT activation in a Samoan population with obesity. Furthermore, following modifications in the cold exposure protocols, I observed that BAT is activated at a wide range of temperatures, warranting further validation of current field methods assessing BAT.

This work suggest that BAT is activated in Samoans at mild cold exposure, despite their warm climates. This indicates that this cold activated organ may be metabolically active across all populations and may have contributed to adaptation and successful human expansion across different environments. This work also revealed that BAT may be using both glucose and lipids as fuel sources but has little effect on blood cholesterol levels in Samoans. These findings indicate that BAT has potential health benefits, such as reducing the risk of type II diabetes, in populations with obesity.

Finally, I found that BAT was activated at different ranges of cold exposure within the same population, emphasizing the variation in its activity between individuals.

Not only do these findings call for further validation of the current BAT inferring protocols, but they also suggest that in non-cold habituated populations, BAT may be activated at any temperatures perceived as cold. My findings underline the importance of considering the inter-individual variation in BAT activity when developing evolutionary or health-related arguments centering around BAT. This dissertation provides additional data on BAT activity needed to understand its variation and metabolic effects in humans. This work contributes to the field of anthropology by providing evidence for the adaptive role of BAT in human global dispersal and highlighting its importance in metabolic health. Based on my findings, future work may identify further individual and population-specific characteristics of BAT, strengthening evolutionary theories on human cold adaptation and providing evidence for potential manipulation of BAT in health care among Samoans and others.