Energetic Constraints on Immune Activation: Comparing CRP and Body Composition in Daasanach Pastoralists and NHANES Data

Abstract

The epidemiological transition represents a major challenge for the future of global health, as the burden of disease shifts from infectious to noncommunicable diseases in populations worldwide. This epidemiological transition is accompanied by a change in immune system activity on an individual level, as acute immune activation is used to defend against pathological threats while chronic immune activation underlies the development of chronic noncommunicable diseases. Life history theory provides an evolutionary framework for understanding why humans are vulnerable to states of chronic inflammation. This thesis aims to test the hypothesis that energetic constraint limits chronic immune activation by assessing the relationship between body composition and inflammatory activity in two populations at different points in the epidemiological transition: the Daasanach, a semi-nomadic pastoralist group in Northern Kenya, and those living in the United States. Linear models were used to assess the relationship between C-reactive protein, a biomarker of immune activity, and three metrics of body composition: body mass index, body fat percentage, and skinfold measures (Daasanach only). We found a significant positive association between body fat and CRP in both populations, supporting the hypothesis that increased long-term energetic availability permits higher immune activation. This work contributes to a larger body of ecological immunology, suggesting that, as populations undergo the epidemiological transition, increased energetic availability may enable chronic inflammatory states that contribute to non-communicable disease risk.