Can Stress Make You Susceptible To Infections?

Nothing makes it more depressing than making it to your holiday destination after a crazy period of work and suddenly becoming sick. That sucks.  It happened to me on a recent trip to Israel and I was not happy with my immune system. But was it my fault? Had I pushed myself too hard? What has stress got to do with our ability to fight infection?   

Our health is dependent on our ability to cope with the environment. This requires the integration of many systems within the body to help maintain homeostasis. Our stress and immune responses both play an integral role in this process. While the stress response helps us cope with factors in our external environment, the immune response helps us cope with factors, primarily damage and infectious agents, within our internal environment. 

Given that both systems are crucial to our survival, they cannot function autonomously from one another. In fact, they are fully integrated with one another via the nervous and hormonal systems. Generally speaking, the nervous system provides rapid yet quickly fading responses while the endocrine system produces slower acting, yet prolonged responses.  

This is an important concept because the effects of stress on the immune system, and vice versa, are dependent on whether the response is acute or chronic. We are well-equipped to deal with acute stress or acute immune activation, but not chronic forms of either. Unfortunately, when stress or immune function is chronic, it can break us down over time. Guess which version of stress most of us suffer from? Of course, it is the chronic version.

Effects of chronic immune activation on the stress response

The sickness response is a prime example of how the immune system affects stress. Inflammation from immune activation alters behavior, producing a state of social withdrawal, depression, anxiety, lethargy, loss of appetite, sleepiness and failure to concentrate. Essentially, activation of the immune response partitions resources towards fighting infection and away from adapting to the external environment. So this explains at least why I become even more of a social hermit when I am unwell. 

Over the short term this also works out well for people around me. Social withdrawal decreases the spread of infection within groups. Decreased physical activity and activation of the stress response partitions limited energy resources towards fighting an infection or healing an injury. As a result, there is quick resolution of the infection and a return to normal. Perfect, thank you immune system. 

But if inflammation becomes chronic, this sickness behavior becomes persistent (1, 2). Alterations in both the nervous and endocrine (hormonal) systems set in, altering physiology to promote both depression and fatigue. Many aspects of our modern lifestyle promote this chronic state of inflammation. Factors such as poor diet, sedentary behavior, obesity, poor sleep, and chronic stress – all factors discussed in this blog series.  Have I mastered most of these factors? Yes, but one – chronic stress. I am a long way from mastering it (open admission here). It is perhaps no surprise as I, like most people, are never taught how to manage and deal with emotions and stress as a child so how can we expect to be masters as adults. 

Chronic inflammation contributes to disruptions in physiological well-being but severe infection can also alter our stress-response long term. Studies show that infection early in life impairs stress resilience in mice (3) and that sepsis in adult humans is a significant risk factor for the development of stress-disorders such as post-traumatic stress syndrome (4).  Studies like these certainly show how much of a bi-directional relationship this is and remind me of the importance to try and look after my stress and immune system. 

Effects of chronic stress on immune function

Just as chronic activation of the immune system promotes a maladaptive stress response, chronic stress does the same to the immune system. During the acute response to stress, activation of the sympathetic nervous system causes the release of short-acting stress hormones called adrenaline and noradrenaline. These mobilise resources towards fight or flight within seconds. For example, someone jumps out from behind a door to scare you –  the reaction you feel is the action of adrenaline and noradrenaline. 

During the response to a prolonged stressor, such as constant impending work deadlines, the endocrine hormone cortisol is released from the adrenal gland to promote a more prolonged response, from hours to days. Cortisol has a powerful effect on our physiology; it makes our stress response stronger by making us more sensitive to adrenaline. It also acts as a strong anti-inflammatory, depressing immune function so that resources are partitioned towards surviving the threat from our environment.

But did you know, when stress is acute, this entire process makes the immune system more efficient (5). Inflammation is kept in check while immune cells flock to areas where pathogens are likely to slip in. The response to regular exposure to acute stressors is immune-enhancing.  This is why exercise is good for the body – it is a short term acute stressor. 

Unfortunately, when stress is chronic, lasting days, it impairs immune function (5). Continuous exposure to cortisol promotes a form of cortisol resistance where both the anti-inflammatory and immune trafficking effects are lost. It also promotes factors that increase inflammation such as hyperglycemia (high blood sugar) and may promote autoimmunity (when our immune system attacks healthy tissue) due to persistent inflammation. Yes, you can get diabetes from stress. 

Early life stress can also be problematic to both the stress response and immunity (6). Early life stressors that are either prolonged or very traumatic, such as sexual abuse, have a way of re-wiring our stress response, making us more sensitive to stressful experiences later in life. Furthermore, adults with early life stress have higher levels of inflammatory markers and viral reactivation of the Epstein Barr Virus than healthy controls. Also, when comparing the desired immune response to vaccination (which is antibody formation) in chronically stressed caretakers to that of control individuals, the carers response was severely blunted. (7) This points to a significant effect of the psychosocial environment on our ability to fend off infections.

Manage and reduce your stress levels – stay healthy

Both the stress and immune response are important for our survival. The stress response helps promote adaptation to external stressors while the immune response helps respond to internal stressors. Successful adaptation to either type of stressor is contingent upon the proper partitioning of resources to overcome it.

Throughout our evolutionary history, our exposures to both stress and infection have been acute. You get exposed to infection or stress, you adapt, and you move on. Therefore, we are well-equipped to deal with acute stress and infection. But chronic stress and infection are a different matter; we are not well-equipped for either.

Unfortunately, our modern existence presents challenges as both can become chronic. Chronic stress, particularly psychological stress, impairs our immune function making us more susceptible to infection. Furthermore, aspects of our modern life create chronic inflammation, promoting chronic stress. These two aspects of our modern lifestyle feed into one another, making us more susceptible to stress and infection.

References

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6658985/

2. https://link.springer.com/chapter/10.1007/978-3-030-16996-1_6

3. https://www.sciencedirect.com/science/article/pii/S0889159118304409

4. https://www.ncbi.nlm.nih.gov/pubmed/25760659

5. https://aacijournal.biomedcentral.com/articles/10.1186/1710-1492-4-1-2

6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465119/

7. https://www.ncbi.nlm.nih.gov/pubmed/18040814

This is a guest post. The opinions expressed are the writer’s own.