Abstract
Stress, a ubiquitous part of daily human life, has varied biological effects which are increasingly recognized as including modulation of commensal microorganisms residing in the gastrointestinal tract, the gut microbiota. In turn, the gut microbiota influences the host stress response and associated sequelae, thereby implicating the gut microbiota as an important mediator of host health. This narrative review aims to summarize evidence concerning the impact of psychological, environmental, and physical stressors on gut microbiota composition and function. The stressors reviewed include psychological stress, circadian disruption, sleep deprivation, environmental extremes (high altitude, heat, and cold), environmental pathogens, toxicants, pollutants, and noise, physical activity, and diet (nutrient composition and food restriction). Stressors were selected for their direct relevance to military personnel, a population that is commonly exposed to these stressors, often at extremes, and in combination. However, the selected stressors are also common, alone or in combination, in some civilian populations. Evidence from preclinical studies collectively indicates that the reviewed stressors alter the composition, function and metabolic activity of the gut microbiota, but that effects vary across stressors, and can include effects that may be beneficial or detrimental to host health. Translation of these findings to humans is largely lacking at present. This gap precludes concluding with certainty that transient or cumulative exposures to psychological, environmental, and physical stressors have any consistent, meaningful impact on the human gut microbiota. However, provocative preclinical evidence highlights a need for translational research aiming to elucidate the impact of stressors on the human gut microbiota, and how the gut microbiota can be manipulated, for example by using nutrition, to mitigate adverse stress responses.
Highlights
The human body is host to trillions of microorganisms collectively known as the human microbiota (Huttenhower et al, 2012; Ding and Schloss, 2014)
Preclinical studies clearly demonstrate that gut microbiota composition and activity is malleable over shorter time frames, and influenced by psychological, physical, and environmental stressors (Figure 1)
Military personnel frequently operate in austere environments in which they are exposed to a variety of stressors that challenge health, cognition, and physical function
Summary
The human body is host to trillions of microorganisms collectively known as the human microbiota (Huttenhower et al, 2012; Ding and Schloss, 2014). Dysbiosis has been associated with multiple chronic diseases such as obesity and associated cardiometabolic diseases (Turnbaugh et al, 2009), inflammatory bowel disease (Sartor, 2008), colon cancer (O’Keefe, 2016), autoimmune diseases (Vaahtovuo et al, 2008; Russell et al, 2012), and psychological disorders (Luna and Foster, 2015; Leclercq et al, 2016) among others (Tremaroli and Backhed, 2012) These associations underlie extensive interest in identifying factors causing dysbiosis, and in developing strategies aiming to leverage the gut microbiota’s tremendous genetic potential for health benefit
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