Health is impacted by much more than what you eat. Health is also influenced by how you live. How active you are, how much you sleep, how much stress you’re under, how much time you spend outside and in nature…. all these things have just as much of an impact on your physical and emotional health as the foods on your plate.
I cannot stress enough (pardon the pun) the negative impact that chronic stress has on your health. In fact, stress contributes to the development and/or worsens all disease, from increasing susceptibility to the common cold to being a major contributor to stimulating the immune system in autoimmune disease. Stress is a bigger predictor of cardiovascular disease than any other factor.
However, often, these lifestyle factors are far harder to prioritize than drastically altering the foods we eat. I wrote these very insightful words on page 144 of The Paleo Approach:
If you do not manage stress, it will completely undermine all the other positive changes you make.
And I can tell you from personal experience, that this is absolutely true.
Chronic stress is known to affect health in a variety of ways, including causing the development of metabolic syndrome (the nasty combination of obesity, insulin resistance, and high blood pressure), dysregulation of the hypothalamic-pituitary-adrenal axis along with sympathetic nervous system activation, sleep disturbances, systemic inflammation, impaired immunity functions, blood coagulation and fibrinolysis, and poor health behaviors (chronic stress causes increased appetite, cravings for energy-dense foods, and uninhibited eating behaviors). Whether you have adopted the Paleo diet to lose a few pounds, increase performance at the gym, or manage a chronic health problem, stress management is critical for your success.
What Is Stress?
It may seem a bit facetious to explain what stress is. Chances are really good that you already know exactly what stresses you have in your life. However, it’s important to differentiate between acute stress and chronic stress.
Historically, all stress was acute and would include situations such as being chased by a lion or slipping off the edge of a cliff. During these events, the fight-or-flight response is activated, and cortisol and adrenaline work together to ensure survival. At the end of the event, you are either dead (because you fell from the cliff onto craggy rocks four hundred feet below) or alive and safe (because you grabbed onto a branch as you slipped off the cliff and pulled yourself back up to safety). In either case, there is no need for the body to continue producing adrenaline and excess cortisol (more on this below). Levels return to normal (unless you’re dead, of course), and you go on your merry way.
Chronic stress is that unrelenting stress that never goes away. It can be at a low level, perhaps the stresses we all experience from having a job, raising kids, and having to make ends meet. It can be moderate, perhaps from an impending deadline or exam, your kids getting into trouble at school, or ripping your favorite shirt. It can also be high, such as illness, divorce, or a death in the family. What’s different about chronic stress is that it’s never over. There’s no big relief at the end before you go on your merry way. It’s always there, having its insidious effects that build up over time. How quickly and severely the effects of chronic stress are felt depends on the severity of the stress and your resilience (more on that below too).
How does stress contribute to disease?
The best understood mechanism is the impact of stress on the immune system. Inflammation is a component of every disease, or every health condition. Worse, it’s part of the pathogenesis–meaning how a disease develops–of every chronic health condition. Inflammation is controlled (or at least is supposed to be controlled) by the immune system. This doesn’t mean that inflammation is the sole causes of chronic disease, but that it is necessary for chronic disease to develop. If you regulate the immune system so that there is not inflammation, you prevent the disease.
The same is true of stress. It’s not the sole cause (at least, there isn’t any research to prove that it is). Bur rather, it contributes to the development of disease, so if you suffer from chronic stress, you increase your risk of getting sick. In order to understand how being stuck in traffic or a deadline at work can directly impact how your immune system functions, it helps to describe what’s happening physiologically inside your body when you’re late for an important meeting at work.
The HPA Axis
The hypothalamic-pituitary-adrenocortical axis (the HPA axis) is responsible for the flight-or-fight response, i.e., how the body responds to stress. The HPA axis is made up of the complex communication between three organs:
- The hypothalamus: The part of the brain located just above the brain stem and responsible for a variety of activities of the autonomic nervous system, such as regulating body temperature, hunger, thirst, fatigue, sleep, and circadian rhythms
- The pituitary gland: A pea-shaped gland located below the hypothalamus that secretes a variety of important hormones, such as thyroid-stimulating hormone, human growth hormone, and adrenocorticotropic hormone
- The adrenal glands: Small, conical organs on top of the kidneys that secrete a variety of hormones, such as cortisol, epinephrine (also known as adrenaline), norepinephrine, and androgens
The hypothalamus (which receives signals from the hippocampus, the region of the brain that amalgamates information from all the senses and can thus perceive danger and make decisions) releases a hormone called Corticotrophin Releasing Hormone (CRH), which signals to the pituitary gland to release a hormone called Adrenocorticotropic Hormone (ACTH), which signals to the adrenal glands to secrete cortisol as well as catecholamines (like adrenalin).
Cortisol has a huge range of effects in the body, including controlling metabolism, affecting insulin sensitivity, affecting the immune system, and even controlling blood flow. If you’re running away from a lion, all these effects (including the combined effects of catecholamines and some direct effects of CRH) combine to prioritize the most essential functions for survival (perception, decision making, energy for your muscles so you can run away or fight for your life, and preparation for wound healing) and inhibit non-essential functions (like some aspects of the immune system especially not in the skin, digestion, kidney function, reproductive functions, growth, collagen formation, amino acid uptake by muscle, protein synthesis and bone formation).
Cortisol also provides a negative feedback to the pituitary and the hypothalamus. It’s the body’s way of saying “hey, we got the signal that we’re supposed to be stressed now, thanks, we’re on it!”. If the stressful event has ceased (the lion gave up and left), this is what deactivates the HPA Axis. Of course, if a stressor is still being perceived (that lion is still there), the HPA axis remains activated. And this is why chronic stress (deadlines, traffic, sleep deprivation, teenagers, divorce, being sick, being inflamed, alarm clocks, bills, and internet trolls) is such a problem. All those essential functions suppressed by high cortisol never get a chance to be prioritized.
Cortisol and the Immune System
Cortisol has profound effects on the immune system and is required for normal wound healing and for fighting infection. Studies have shown that acute (short-duration and intense) stressors (like running away from a lion) induce a redistribution of immune cells in the body, resulting in enhanced immune function in organs like the skin. White blood cells are released from bone marrow and travel to the skin during acute stress, most likely in preparation for wound healing. Other aspects of the immune system are activated in anticipation of being needed. In this situation, cortisol enhances the immune system response.
However, what is beneficial in acute stress becomes quite the troublemaker during chronic stress. There is a spectrum of responses by the immune system to a high-cortisol environment, probably reflecting different effects at different cortisol levels and in the presence of other chemicals produced by the body and in the context of different levels of sensitivity to cortisol. The waters are murky in terms of the details, but what is universally accepted is that chronic stress causes immune system dysfunction.
Cortisol alters the chemical messengers of inflammation (called cytokines) secreted by cells in the immune system. This changes how the immune system communicates with itself, turning on some aspects of the immune system (like the parts of the immune system that attack foreign invaders or that produce generalized inflammation), while turning off other aspects of the immune system. There are a wealth of studies to show that high cortisol causes inflammation.
The exact response of the immune system to chronic stress seems to depend on other physiologic factors, such as hormones, cytokines, and neurotransmitters, as well as the state of activation of the immune system (live if you’re already fighting a cold virus, for example). Even genes may play a role in how the immune system responds to chronic stress. The immune system is complex and only just beginning to be understood, but the bottom line is that chronic stress greatly diminishes its effectiveness.
Chronic stress has been unequivocally shown to increase susceptibility to a variety of conditions, including autoimmune disease, cardiovascular disease, metabolic syndrome, osteoporosis, depression, infection, and cancer.
Cortisol and Leaky Gut
What exactly is a “leaky gut”? The gut is a barrier between the inside of your body and the outside world. Yes, as unintuitive as it may be, the stuff inside your digestive tract is actually outside your body. But, the gut is a very unique barrier. Its job is to let important nutrients inside the body while keeping everything else out. This makes it a highly selective semi-permeable barrier. Nutrients enter the body through a variety of tightly controlled mechanisms.
What forms this highly selective semi-permeable barrier is a single layer of highly specialized cells called enterocytes. And right on the other side of that barrier is 80% of our body’s immune systems, acting as a sentinel, ready to attack anything that might try to cross the barrier.
A leaky gut, or more technically “increased intestinal permeability”, means things can get across the gut barrier that aren’t supposed to. This happens when either the enterocytes are damaged or the complex structures that glue the enterocytes to each other are damaged. What leaks into the body isn’t big chunks of food, but a variety of small substances—like incompletely digested proteins, bacteria or bacterial fragments, infectious organisms, and waste products—which all stimulate the immune system on the other side. Some substances cause generalized bodywide inflammation (for example, bacterial fragments from those good bacteria that live in our digestive tracts but are supposed to stay there can stimulate inflammation which can then travel throughout the body). Some stimulate targeted attacks by the immune system (for example, a food intolerance or allergy could result from incompletely digested food proteins leaking into the body). The many symptoms and health conditions related to leaky gut are caused by this stimulation of the immune system.
One of the biggest impacts chronic stress has on those with autoimmune disease may be cortisol’s direct action on the enterocyte tight junctions. It is well understood that cortisol opens up the tight junctions and increases permeability of the gut barrier (although the molecular details of this action are still being investigated). Given the growing list of health conditions linked to a leaky gut, including the further impact that leaky gut has on the immune system, this is another tick in the why-to-manage-stess column.
Managing Chronic Stress
Chronic stress is best handled from two sides: reducing stressors and increasing resilience. Resilience is the ability to adapt successfully in the face of stress and adversity. This doesn’t mean that stressful events don’t affect you, but rather that you can handle them without the wheels falling off your cart. Activities that increase resilience include yoga, meditation, walking, laughing, and social bonding. Getting sufficient sleep may be the best tool for reducing the effects of psychological stressors.
How your body responds to chronic stress is also affected by diet (at least in part). Studies have shown that a deficiency in omega-3 fatty acids exaggerates stress responses, but that supplementation with fish oil reduces cortisol secretion in response to stress. Habitual coffee drinkers also have exaggerated cortisol release in response to chronic stress.
I’ll be discussing stress management strategies in future posts. For now, consider asking for help, saying no, going out for a walk, getting a massage, giving up coffee, getting more sleep, and eating more fish.
There is a ton more detailed information on the physiologic effects of chronic stress, as well as tons of tips on how to manage it, and including hundreds of scientific references in my book, The Paleo Approach.
There’s also a wealth of information showing the benefits of social connection in stress management (see this post).
Some additional references:
Barbadoro, P., et al., Fish oil supplementation reduces cortisol basal levels and perceived stress: a randomized, placebo-controlled trial in abstinent alcoholics, Mol Nutr Food Res. 2013;57(6):1110-4
Cohen, S et a., Psychological Stress and Disease, JAMA. 2007;298(14):1685-1687. doi:10.1001/jama.298.14.1685.
Cohen, S., et al., Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk, Proc Natl Acad Sci U S A. 2012;109(16):5995-9
Dhabhar, F. S. and McEwen, B. S., Acute stress enhances while chronic stress suppresses immune function in vivo: a potential role for leukocyte trafficking, Brain Behav Immun. 1997;11:286-306
Dimsdale, J.E. Psychological Stress and Cardiovascular Disease, J Am Coll Cardiol. 2008;51(13):1237-1246. doi:10.1016/j.jacc.2007.12.024Glaser, R., et al., Evidence for a shift in the Th1 to Th2 cytokine response associated with chronic stress and aging, J Gerontol A Biol Sci Med Sci. 2001;56:M477-M482
Jefferies, W. M., Cortisol and immunity, Med Hypotheses. 1991;34(3):198-208
Melamed, S., et al., Burnout and risk of cardiovascular disease: Evidence, possible causal paths, and promising research directions Psychological Bulletin, Vol 132(3), May 2006, 327-353.
Wu, G., et al., Understanding resilience, Front Behav Neurosci. 2013;7:10