When Stress Doesn’t Switch Off: How Persistent Stress Shapes Your Health (Part 1 of 2)
The nervous system matters for our health
Stress shapes our physical health in ways that are easy to overlook. In this first part, I look at how the nervous system responds to stress, what happens when that response doesn't switch off, and why it matters for our health. In Part 2, I look at what we can do about it through nutrition, sleep, light and breath.
Our nervous system is physically connected to all of our organs via a network of nerves. It has two opposing branches. When we are in a stressed (sympathetic) state, the body prioritises getting glucose to our muscles and keeping blood moving. When we are in a rested (parasympathetic) state, it prioritises digestion, repair and reproduction. The two cannot be in charge at the same time.
The vagus nerve is a principal component of the parasympathetic nervous system, and it is a surprising one. Around 80% of its fibres are afferent, meaning they carry information up from the body to the brain, and only 20% carry instructions back down [1]. It is largely a listening nerve: our gut and organs reporting to the brain on whether things feel safe. It can sense metabolites produced by our gut bacteria, and through what is known as the cholinergic anti-inflammatory pathway it helps to dampen inflammation and reduce intestinal permeability. Stress inhibits vagal activity, and low vagal tone has been described in people with irritable bowel syndrome and inflammatory bowel disease [1].
Cortisol is not (always) the enemy
We need cortisol. It helps us get up in the morning, it keeps us motivated through the day and it gets us moving when we face a threat. Acute, short-term stress is part of life, and the body has a natural regulatory feedback loop that lets us respond and then recover.
The problem comes when stress becomes persistent. Interestingly, the picture is not simply "too much cortisol". In a small study, volunteers were exposed to a cold virus and found that people who had recently experienced a long-term stressful event showed glucocorticoid receptor resistance which means that their immune cells had become less responsive to cortisol's signal to switch inflammation off. Those with the greatest resistance were more likely to go on to develop a cold [2]. This loss of sensitivity may be one way prolonged stress allows inflammation to escalate in the body when we are stressed and why we are more at risk of infection and chronic disease.
When the body runs flat
The pattern I see most often with clients who do a test of their cortisol levels is not high cortisol, but the opposite. By the time people come to see me they are typically tired and flat. Reduced cortisol output (hypocortisolism) has been reported in people living under chronic stress, and in conditions such as chronic fatigue syndrome and fibromyalgia, although the mechanisms are still poorly understood [3]. It has been proposed that this may be a protective adaptation, with the body down-regulating its exposure to cortisol after a prolonged period of excess [4]. This is not the same thing as "adrenal fatigue", which is not a recognised medical diagnosis, and persistent tiredness has many possible causes, so it is always worth speaking to your GP.
How our body manifests persistent stress
When stress persists, the effects can be felt in many ways: disrupted sleep, energy crashes, poorer digestion, nutrient depletion, inflammation, reduced thyroid function, weight gain and more difficult menopause symptoms. Many of these then feed back into the stress response themselves, which is why health is so much harder to restore when the body is in a stressed state.
Why stress can hit harder as hormones change
Stress and our hormones influence each other in both directions. Repeated or chronic stress dampens the signals that drive the ovaries, and cortisol can inhibit the release of oestrogen and progesterone [5]. This matters because those hormones also support the brain chemistry of calm. Oestrogen influences serotonin signalling [5], and progesterone is converted into neurosteroids that act on GABA receptors, our main calming pathway [6]. You can see this in premenstrual symptoms, which tend to appear when oestrogen and progesterone fall in the days before a period, indicating women experience vulnerability to hormonal fluctuation and stress [6].
During the menopause transition, hormone levels do not simply decline. They swing erratically, and for some women this seems to make the stress response more sensitive. In one study of women going through the menopause transition, those with greater swings in oestradiol over 14 months had more depressive symptoms, but only if they had also had very stressful life events recently [7]. In other words, stressful experiences land harder when our hormonal buffer is less steady.
To compound this, there also appear to be differences in how the brain handles threat. Women are more prone to anxiety disorders, and in experiments where a threat is unpredictable, women show greater sustained anxiety than men, although not a stronger startle response to a clear, immediate threat. This may relate to sex differences in the brain circuits involved in anticipating threat, including a region called the bed nucleus of the stria terminalis [8].
Put together, as hormones fluctuate and fall, the systems that scan for threat and the systems that calm us become less steady, and past stresses we were once able to tolerate can feel harder to handle. Our defences are lower. Not every woman will notice this, but it will be the experience for some.
Balance can be restored
None of this is a sign that your body is failing. A stressed nervous system is doing exactly what it was designed to do: protecting you, based on everything it has learned. As hormones change with age our defences are lower and we are in a more vulnerable state and our body feels unsafe. However safety is a physiological signal, and balance can be restored. Safety can be communicated to the body through what we eat, how we sleep, the light we are exposed to and the way we breathe.
That is what Part 2 is about: Eating, Sleeping and Breathing Your Way to a Calmer Nervous System.
If you have any questions, you are welcome to contact me directly at eleanorreidnutrition@gmail.com. You can also book a free 15-minute call with me at eleanorreidnutrition.com to see how nutritional therapy could be helpful for you.
Thank you for reading
Warm wishes, Eleanor
This article is for general information only and is not a substitute for individual medical advice.
References
Bonaz B, Bazin T, Pellissier S. The vagus nerve at the interface of the microbiota-gut-brain axis. Front Neurosci. 2018;12:49. doi:10.3389/fnins.2018.00049
Cohen S, Janicki-Deverts D, Doyle WJ, et al. Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk. Proc Natl Acad Sci U S A. 2012;109(16):5995-5999. PMID: 22474371
Heim C, Ehlert U, Hellhammer DH. The potential role of hypocortisolism in the pathophysiology of stress-related bodily disorders. Psychoneuroendocrinology. 2000;25(1):1-35. PMID: 10633533
Fries E, Hesse J, Hellhammer J, Hellhammer DH. A new view on hypocortisolism. Psychoneuroendocrinology. 2005;30(10):1010-1016.
Toufexis D, Rivarola MA, Lara H, Viau V. Stress and the reproductive axis. J Neuroendocrinol. 2014;26(9):573-583.
Gordon JL, Girdler SS, Meltzer-Brody SE, et al. Ovarian hormone fluctuation, neurosteroids, and HPA axis dysregulation in perimenopausal depression: a novel heuristic model. Am J Psychiatry. 2015;172(3):227-236. doi:10.1176/appi.ajp.2014.14070918
Gordon JL, et al. Estradiol variability, stressful life events, and the emergence of depressive symptomatology during the menopausal transition. Menopause. 2016;23(3):257-266. PMID: 26529616
Grillon C. Greater sustained anxiety but not phasic fear in women compared to men. Emotion. 2008. PMCID: PMC2669676
Comments