Dutch Courage: how alcohol interacts with our nervous system

Chloe Marschner

Every year we learn more about how alcohol affects the body. One rising area of interest for researchers is how our drinks interact with our nervous system. The vagus nerve, part of our nervous system, is often implicated as it is involved in a whole host of internal body regulatory processes. Fusing together a number of findings from the last decade, we explore the complex interactions of the vagus nerve, the nervous system and alcohol.

To set the scene, the vagus nerve is the tenth cranial nerve – one of the main nerves involved in connecting our brains to our guts. This has been of particular interest recently, due to growing evidence that the connection between the brain and the gut affects depression. The vagus nerve controls such bodily functions as our digestion, immune system and heart rate, and spans from our brain to other organs like our heart and lungs. Much of the control it has over our organs is involuntary, and it is part of our parasympathetic nervous system. In other words, it is part of the system which works to keep our bodies at an even keel.

When we introduce alcohol into our body, the vagus nerve doesn’t exactly respond favourably. In normal circumstances, the vagus nerve works to reduce inflammation in all of the organs it reaches, particularly the gut and the liver.[1] It does this through the release of acetylcholine, which is a neurotransmitter that is central to the working of our nervous system. Usually, acetylcholine would be released onto specific receptors (known as nicotinic receptors of the alpha7-subtype – or, alpha7-nicAChRs for short). When we drink alcohol, we are also actually inhibiting, or blocking, the workings of these receptors. This means that the vagus nerve’s normal process of reducing inflammation is interrupted, and thus leading to inflammation – the kind which is often found in alcohol-induced damage of organs. Another adverse effect of too much alcohol interacting with the vagus nerve is vagal neuropathy. This is a type of nerve damage, which people often experience as laryngeal discomfort or a chronic cough. This would certainly more be the case with chronic and excessive alcohol consumption rather than a pint here and there, but it is clear to see how alcohol has an adverse effect upon the vagus nerve.

Another way in which the vagus nerve interacts with alcohol is by being part of the dorsal vagal complex (DVC)[2]. This complex is formed of several areas of our brain and nervous system, which helps the body oscillate between relaxation and arousal. A large component of the DVC is the autonomic nervous system (including the sympathetic and parasympathetic nervous systems), which primarily act to return our bodies to a state of calm. Think reducing our heart rate, or producing saliva to help digest our food or tears to moisten our eyes. This entire complex, including the vagus nerve, also acts to control our intake of rewards – like alcohol, for example. Alcohol rewards us with feel-good chemicals, social lubrication, a mostly pleasurable taste, and sometimes self-medicative effects. So perhaps unsurprisingly, research is beginning to show what a powerful role the DVC plays in alcohol use disorder (AUD), as well as our more everyday behaviours around alcohol. To really ram things home, the DVC brain chemicals also are directed towards brain areas involved in the “feeling bad” experience of withdrawing from alcohol. When combined, this makes a potent mix in our brains, with the DVC accentuating the “feeling good” and “feeling bad” of the addictive cycle of drinking alcohol. This kind of understanding of how the nervous system affects drinking behaviour is very useful to suggest new treatment possibilities for those suffering with alcoholism.

Considering the vagal nerve further, research has also shown many more interactions when we drink alcohol. For example, one study allowed participants to drink precisely-measured-out alcohol whilst measuring their heart activity.[3] By comparing these heart readings with readings from when they were just drinking water, the researchers concluded that drinking alcohol reduces cardiac vagal tone. In other words, alcohol lowers the level of activity of our vagal nerve as it reaches our heart. This means the connection between our parasympathetic nervous system and our organs is weakened overall, so it’s harder for us to return to a state of calm. Low vagal tone has been associated with a sensitivity to stress, as well as poorer regulation of emotions.[4] (This is also a great area of interest for those concerned with how states of the body (physiological) interact with states of the mind (psychological).[5]) Heightened stress and arousal can increase the likelihood other medical issues, like high blood pressure, heart disease, obesity, asthma and arthritis.[6] Thus, though we are never really aware of it, the vagal nerve actually plays a large role in how alcohol can have tangential impacts on our long term health.

As well as this, the fact that alcohol inhibits, or lowers the activity of, our parasympathetic nervous system can also interfere with our sleep – as one study showed by measuring the electrical activity of ten students for 24 hours after they’d had a drink.[7] Because of this parasympathetic inhibition, the sympathetic nervous system takes over. This system is involved in our stress responses like an increased heart rate and sweating – otherwise known as fight or flight responses – and these are not exactly conducive to a restful night’s sleep. Thus, alcohol overall inhibits the ability of our parasympathetic nervous system to ease our body from arousal to calm, and can affect us even when we are not awake.

Through all of this research over the past two decades, we are starting to gather a picture of how drinking alcohol affects the vagus nerve, and our nervous systems in general. We are also gleaning more about the relationship between the body and the mind – and how the parasympathetic nervous system connects them. Knowing then how alcohol interacts with the nervous system, we can also begin to offer more tailored advice and therapeutic treatments for those suffering with chronic alcohol consumption.

References

[1] Littleton, J.M. (2011) Alcohol, the vagus nerve and multi-organ inflammation. Grantome. Available at: https://grantome.com/grant/NIH/R21-AA020188-01

[2] Keller, B.N., et al. (2022) Involvement of the Dorsal Vagal Complex in Alcohol-Related Behaviors. Frontiers in Behavioral Neuroscience. 16. Available at: https://www.frontiersin.org/articles/10.3389/fnbeh.2022.801825/full

[3] Reed, S.F., Porges, S.W., Newlin, D.B. (1999) Effect of alcohol on vagal regulation of cardiovascular function: contributions of the polyvagal theory to the psychophysiology of alcohol. Exp Clin Psychopharmacol. 7,4. 484-92. Available at: https://pubmed.ncbi.nlm.nih.gov/10609983/

[4] McLaughlin, K.A., Rith-Najarian, L., Dirks, M.A., Sheridan, M.A. (2015) Low vagal tone magnifies the association between psychosocial stress exposure and internalizing psychopathology in adolescents. J Clin Child Adolesc Psychol. 44,2. 314-28. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4076387/

[5] Laborde, S., Mosley, E., Thayer, J.F. (2017) Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research - Recommendations for Experiment Planning, Data Analysis, and Data Reporting. Front Psychol. 8, 213. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5316555/

[6] Bhandari, S. (2021) The Effects of Stress on Your Body. WebMD. Available at: https://www.webmd.com/balance/stress-management/effects-of-stress-on-your-body

[7] Sagawa, Y., et al. (2011) Alcohol Has a Dose-Related Effect on Parasympathetic Nerve Activity During Sleep. Alcoholism Clinical and Experimental Research. 35, 11. 2093-100. Available at: https://www.researchgate.net/publication/51578260_Alcohol_Has_a_Dose-Related_Effect_on_Parasympathetic_Nerve_Activity_During_Sleep