Countries that are becoming more exposed to Westernization have experienced many positive health impacts, such as decreases in infectious disease rates. At the same time, however, there have been some negative consequences, such as increases in type 2 diabetes (T2DM) patients in these developing countries. T2DM is linked to disruptions in energy balance and increases in systemic inflammation. Interestingly, helminth infections – i.e., the parasitic worms that can reside in the intestines – have been previously shown to enhance glucose tolerance in animal models as well as induce anti-inflammatory immune responses. Researchers sought to explore this relationship in humans, hypothesizing that insulin resistance is lower in subjects with soil-transmitted helminth infection.
A homeostatic model assessment for insulin resistance (HOMAIR) test was used to examine insulin resistance in 646 adult study participants on Flores Island in Indonesia. Soil-transmitted helminth (STH) infection is common on this island. The HOMAIR model measures insulin in blood samples in a well-validated insulin-resistance assay. Stool samples were also collected from the subjects, and microscopy and PCR were used to detect various helminth species.
Of the 646 participants, 424 were STH-infected while 222 were not. In the STH-infected cohort, participants were further categorized by how many different species were found. Body mass index and waist to hip ratio were significantly lower in the STH-infected group, suggesting STH-infection may be beneficial toward glucose metabolism. Furthermore, there was an association between the number of distinct STH species present and HOMAIR. For every additional species found in a subject, there was an incremental decrease in homeostatic insulin resistance.
These experiments display an interesting causal relationship between STH species and insulin resistance, however there were certainly limitations. No association was found between subjects in systemic inflammation in infected versus non-infected groups, failing to elucidate modulations of inflammatory pathways that could be correlated with the observed trends. Additionally, the changes in insulin resistance may be related to a change in body-mass index rather than helminth infection. Specifically, participants located in more rural areas may have more active, healthier lifestyles, and would be subsequently leaner and thus more sensitive to insulin. On top of this, patients with helminths tend to exhibit lower weight in general as these parasites significantly affect metabolism.
Despite these limitations, this study points to an interesting relationship that is deserving of more examination. This epidemiology research will impact global health policy and can offer good perspective as more nations around the world are on the path toward development.