The Stress That Evolution Has Not Prepared Us For
For most people chronic stress has become a regular aspect of modern life, regardless if they are aware of it or not. This chronic stress is fueled and amplified by the relentless bombardment with negative news from the media, in particular the internet: the pandemic, catastrophic climate events, political polarization and a raging war in the middle of Europe are just the most recent examples. On top of that, health books, influencers and social media constantly feed us worrisome and conflicting negative information about our food, dietary habits and our health. This situation has led to what Michael Pollan has rightfully called a national eating disorder epidemic adding anxiety and stress to what normally should be one of our most rewarding times in life, enjoying food with family and friends.
“Our biology has not evolved in an adaptive way to deal with this type of constant … stress exposure”
Our biology has not evolved in an adaptive way to deal with this type of constant and repeated exposure to stress 24 hours a day. The mismatch between our ancient highly effective biological acute stress response systems which is turned on and off quickly by powerful regulatory mechanisms, and this new form of chronic perturbation of the body’s homeostasis (also referred to as allostatic load) is one of the major factors affecting our health.
“Acute, often life-threatening stress has been part of human life for millions of years…”
Acute, often life-threatening stress has been part of human life for millions of years and there has been enough time in our evolutionary history to perfect our biological stress response systems in a way that has not only kept our species alive through natural disasters, wars, famines and pandemics, but also has resulted in the dominance of planet Earth by our species. There are two such systems in our body: the older immune stress response system and the brain’s acute stress response system, and both are often engaged together.
“The engagement of the brain’s and the immune system response generally occurs in synchrony optimizing the outcome.”
The immune system typically responds to an invasion of pathogens (microbes that are harmful to us) with the initial engagement of the innate immune system, like dendritic cells, leading to the recruitment of different immune cells and powerful tools of the adaptive immune system, as well as the release of both inflammatory and anti-inflammatory cytokines. The balance between these opposing forces determines the severity and duration of the infection. The brain also responds to a wide range of perturbations ranging from infections, injuries, psychosocial stressors but also from worry about harmful events happening in the future. Depending on the type and severity of the stressor, the brain responds with the engagement of the two arms of the stress response system, the sympathetic nervous system and the release of cortisol by the HPA axis. The engagement of the brain’s and the immune system response generally occurs in synchrony optimizing the outcome.
“… the worry about being shot remains a persistent stress for a significant segment of the population”
Our organism responds to any situation – in the presence or anticipated to occur in the future – that is perceived as a threat to our integrity and homeostasis by engaging one or both of these stress response systems. While they have evolved and are optimized to respond to infrequent, but life threatening stresses – the poisonous snake, the wild tiger, the severe injury or the infection, for the majority of people in developed countries, these are no longer the kind of stresses we encounter on a regular basis. Unfortunately, the worry about being shot remains a persistent stress for a significant segment of the population as highlighted by the ongoing epidemic of high profile police shootings.
“Our metabolism and the mechanisms controlling our eating behavior are simply not equipped to resist the constant bombardment with commercials promoting unhealthy food…”
Today’s perturbation of our body’s balance most often comes in form of chronic stressors associated with modern life: The chronic psychological stress on our minds generated by the relentless daily bombardment with negative news, worries about the future, increasing competition, and number of challenges associated with a lower socioeconomic status (in plain language, poverty, food insecurity, health conditions). And at the same time, the dietary stress on our metabolism in form of the unhealthy Standard American Diet. Our metabolism and the mechanisms controlling our eating behavior are simply not equipped to resist the constant bombardment with commercials promoting unhealthy food, the grotesque portion sizes in most restaurants and the unhealthy contents of our food, full of saturated fat, sugar, and added chemicals including non-nutritive sweeteners, residues of pesticides in our vegetables and fruits, and microplastic in our seafood.
“The relentless engagement of our stress systems comes at an increasing cost to the health of our bodies and minds.”
Unfortunately, these two type of stressors often occur together, in particular in individuals from lower socioeconomic segments of our society. The relentless engagement of our stress systems comes at an increasing cost to the health of our bodies and minds. Evolution had not foreseen these kind of stressors which we have never experienced as a species. While our stress response systems, the sympathetic nervous system and the HPA axis keep responding in the same way that has been so adaptive for human life, chronic hyperproduction of the stress mediators cortisol and noradrenaline, and chronic systemic engagement of the immune system are responsible for many aspects of our current chronic non-infectious disease epidemic as I have described in detail in The Gut Immune Connection.
Not everybody responds to these challenges in the same way: the responsiveness of our neurological and immunological stress system is influenced by genetic factors and is programmed during the first 18 years of life, starting prenatally, in utero, and postnatally, and will determine our lifetime risks for developing these common chronic diseases. This will result in a situation where two people exposed to the same kind and severity of stress will respond in very different ways: one will remain healthy and live to a 100 years, the other one developing a chronic disease and dying early. Other important factors that have been shown to influence the outcomes of living in a chronically stressful world is the quality of social interactions, and the adoption of a eudaimonic lifestyle, which means doing meaningful things including doing good for others.
If you want to learn more about this topic, you might also be interested in my upcoming book The Mind-Gut-Immune Connection that you can preorder now.
Dr. Emeran Mayer is a Distinguished Research Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA, the Executive Director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience and the Founding Director of the Goodman-Luskin Microbiome Center at UCLA.