Firefighters are at increased risk of developing and dying from several types of cancer, including but not limited to colorectal cancer, esophageal cancer, and lymphoma.[1-4] Firefighters experience several occupational hazards, such as heat stress and occupational chemical exposures during fire suppression, which may increase their risk for cancer.[5-10] For example, polycyclic aromatic hydrocarbons (PAHs) are carcinogens that are formed by the incomplete burning and combustion of organic materials, and are produced in most fires.[5-7] Prior research, as well as our own preliminary work, has shown that firefighters experience varying and increased levels of PAH exposure compared to the general population.[5-7]
However, occupational hazards and the mechanisms by which they may influence cancer risk are understudied among firefighters. The gut microbiome has well-established links with the development of several cancers, and may represent an influential mechanism by which occupational hazards may increase risk for cancer among firefighters.[11 ] Gut dysbiosis, which may potentially be characterized by increased proportions of pathogenic bacteria and lower bacterial diversity, may promote inflammation and immune activation, which in turn may increase risk for cancer. Moreover, PAH exposure has been shown to substantially alter the gut microbiome composition in animal models.[12, 13] Prior research has also documented the gut microbiome metabolizes PAHs in humans. Additionally, high heat exposure, another occupational hazard for firefighters, has been shown to be associated with bacterial dysbiosis in animal models.[14, 15]
The central hypothesis of our study is that occupational exposures (i.e., heat exposure and PAH exposure) will be associated with gut dysbiosis among firefighters. Our primary goal will be to examine associations between heat exposures, PAH exposures, and gut microbiome composition in a convenience sample of 100 Florida firefighters who are participating in the Firefighter Cancer Initiative (FCI). FCI is a longstanding, federal and state-funded research program examining cancer risk and development among a prospective epidemiologic cohort of Florida firefighters. The FCI includes 13 on-going studies, has accrued over 3500 firefighters to-date, and involves strong partnerships with fire service leadership across the state of Florida. We propose to leverage the infrastructure and resources from the FCI to collect microbiome kits from 100 firefighters pre and post active fire exposure, and will also collect comprehensive data regarding their individual and ambient heat and PAH exposures, as well as their sociodemographic, behavioral, and medical history information. Our aims are as follows:
Aim 1: To characterize the gut microbiome of 100 Florida firefighters.
We will analyze the gut microbial composition of our sample, and will compare these findings with uBiome’s reference ranges.
Aim 2: To examine associations between PAH exposure and the gut microbiome of firefighters.
We will measure exposure to PAHs among firefighters during an active fire training exercise using innovative silicone-based wristband technology. We will also measure gut microbiome composition before and twice after the active fire training, to examine the relationships between PAH exposure and change in microbial composition over time.
Aim 3: To examine associations between heat exposure and the gut microbiome of firefighters.
We will measure individual-level and ambient heat exposure among firefighters during an active fire training using wearable thermometers, as well as thermometers within the active fire site. We will also measure gut microbiome composition before and twice after the active fire training, to examine the relationships between heat exposure and change in microbial composition over time.
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