Stress is often perceived as an emotional experience: a feeling of pressure, mental fatigue, or overload that arises in response to demanding situations. However, this perception falls short of what is actually happening within the body. Beyond the psychological aspect, stress activates a series of biological responses capable of modifying the internal functioning of the body, including key processes related to immunity. It is not only about how we feel, but about how the body interprets and responds to those signals.

In this context, science has begun to reveal a much more complex network of interactions than previously understood. The brain, the gut, and the immune system do not operate independently, but rather as parts of an integrated system that communicates constantly. This communication allows changes in one system to have direct effects on the others. Within this network, stress acts as a modulator capable of disrupting internal balance, often without obvious manifestations in the early stages.

One of the central elements in this interaction is the gut microbiome, a diverse community of microorganisms that inhabit the intestine and play essential roles in health. These bacteria are not only involved in digestion, but also contribute to the production of key compounds and the regulation of the immune system. Their balance is fundamental to maintaining an appropriate immune response, and any alteration in their composition can have significant consequences.

Some studies have found that negative psychological states, such as persistent stress, can directly modify the composition of the gut microbiome. This finding reinforces the idea that emotional experiences do not remain confined to the mental domain, but instead translate into concrete physiological changes. Under conditions of stress, a decrease in beneficial bacteria is observed, particularly those associated with protective functions, such as those from the Lactobacillus genus, which play an important role in defense against infections.

The connection between the brain and the gut is not abstract. It is mediated by specific anatomical structures, with the vagus nerve being one of the main communication pathways. This nerve allows bidirectional signal exchange between both systems, enabling the brain to influence intestinal functions and the gut, in turn, to send information that can affect central processes. This continuous interaction is essential for maintaining physiological balance.

Within this system, the Brunner’s glands play a relevant role. Located in the small intestine, these structures help regulate the intestinal environment and, according to available evidence, act as a link between signals coming from the brain and the composition of the microbiome. When their function is compromised due to alterations in nerve signaling associated with stress, an imbalance in bacterial populations occurs, directly impacting the body’s ability to maintain homeostasis.

The consequences of this process are significant. The reduction of beneficial bacteria is associated with increased susceptibility to infections and a less efficient immune response . This suggests that stress not only influences emotional well-being, but can also compromise the body’s ability to defend itself against external threats. This weakening occurs progressively and, in many cases, without obvious symptoms in early stages, making early identification more difficult.

 

Figure 1. Chronic stress alters brain–gut signaling, impairing Brunner’s gland function and disrupting the intestinal environment. This imbalance affects the microbiome and weakens mucosal immune defense.

 

This connection becomes especially relevant when considering complex diseases such as cancer. The immune system plays a critical role not only in defending against infections, but also in identifying and eliminating abnormal cells that could develop into tumors. When immune function is compromised or dysregulated, this surveillance mechanism can become less effective, potentially allowing abnormal cells to persist and evolve. While stress alone is not a direct cause of cancer, its impact on immune balance may influence how the body responds to these early changes.

In addition, the gut microbiome has been increasingly recognized as a key regulator of systemic inflammation and immune signaling, both of which are deeply involved in cancer biology. Alterations in microbial balance may contribute to a pro-inflammatory environment or impair immune responses that are essential for controlling tumor development and progression. This highlights the importance of maintaining physiological balance not only for general health, but also in the broader context of disease prevention and resilience.

Another important aspect is the bidirectional nature of this relationship. Just as the brain influences the gut, the state of the microbiome can affect processes related to behavior and emotional responses. This phenomenon, known as the gut-brain axis, demonstrates that changes in the microbiota have not only physical implications, but also psychological ones. This creates a cycle in which stress alters the microbiome, and an altered microbiome can contribute to maintaining or even intensifying states of stress.

Despite the complexity of this system, current evidence also provides a hopeful perspective. The observed changes are not necessarily permanent. In experimental models, stimulating certain neural pathways or activating specific brain regions allowed the restoration of Brunner’s gland function and the recovery of microbiome balance. This highlights the adaptive capacity of the body and its potential to regain balance when appropriate conditions are restored.

This type of evidence suggests the need to reconsider how health is approached. Beyond treating specific diseases, it becomes important to pay attention to the factors that contribute to maintaining internal balance. In this sense, emotional state is no longer a secondary element, but a key component of comprehensive health care.

 

Figure 2. Gut bacteria can influence cancer in different ways: they change the environment of the gut, can reach and interact with tumor tissue, and affect how the immune system responds.

 

It is important to clarify that stress itself is not an exclusively negative phenomenon. It is part of natural adaptive mechanisms and allows the body to respond to situations that require attention or immediate action. The problem arises when this state is prolonged over time and the body remains in a constant condition of activation. In that scenario, internal systems begin to dysregulate, and the cumulative effects can have a significant impact on health.

In an environment where daily demands favor continuous exposure to stressors, understanding these mechanisms becomes especially important. It is not only about managing stress from an emotional perspective, but also about recognizing its physiological impact and its ability to influence fundamental processes within the body.

In practical terms, this knowledge reinforces the importance of habits that contribute to stress regulation and the maintenance of internal balance. Adequate rest, physical activity, time management, and the creation of mental recovery spaces not only improve quality of life, but can also influence immune system function.

 

Main reference:

Chang, H., Perkins, M. H., Novaes, L. S., Qian, F., Zhang, T., Neckel, P. H., Scherer, S., Ley, R. E., Han, W., & de Araujo, I. E. (2024). Stress-sensitive neural circuits change the gut microbiome via duodenal glands. Cell, 187(19), 5393–5412.e30. https://doi.org/10.1016/j.cell.2024.07.019 

 

Other references:

Ley, R. E., Lozupone, C. A., Hamady, M., Knight, R., & Gordon, J. I. (2008). Worlds within worlds: evolution of the vertebrate gut microbiota. Nature reviews. Microbiology, 6(10), 776–788. https://doi.org/10.1038/nrmicro1978 

Cryan, J. F., & Dinan, T. G. (2012). Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nature reviews. Neuroscience, 13(10), 701–712. https://doi.org/10.1038/nrn3346 

Ley, R. E., Peterson, D. A., & Gordon, J. I. (2006). Ecological and evolutionary forces shaping microbial diversity in the human intestine. Cell, 124(4), 837–848. https://doi.org/10.1016/j.cell.2006.02.017