Vagus Nerve and Inflammation

Inflammation and Chronic Illness

For the past three decades there is growing scientific evidence that prolonged inflammation is the source of many chronic illnesses. Many researchers also believe that most age related illnesses and health issues can be linked to high levels of pro-inflammatory markers in the blood. Chronic inflammation is a strong predictor of cardiovascular disease, old age frailty and a decline in physical and cognitive function. While related to age, these effects can be observed at any age. 

This kind of prolonged elevation in the body’s levels of inflammation should be contrasted against acute inflammation, which is of course the body’s response to injury or infection, and forms a crucial part of the healing process. The problems occur when inflammation remains elevated for prolonged periods of time. 

Vagus Nerve

If levels of inflammation are so important to long term health, it becomes crucial to understand the mechanisms of inflammation, it’s function and how to control it. 

In an excellent paper published in The Journal of Internal Medicine, two scientists, J. M. Huston and K. J.Tracey, described a crucial neural control circuit that acts via the vagus nerve to limit inflammation. They termed it the ‘inflammatory reflex’ and described a mechanism by which the vagus nerve detects pro-inflammatory markers in the body and sends signals back to the brain stem, which in turn triggers action potentials which then travel down efferent pathways of the vagus nerve to the spleen, which is then induced to produce the anti-inflammatory neurotransmitter acetylcholine. 

When this neural circuit is weakened, inflammation can become chronic and out of control. In other words, without a strong and healthy vagus nerve, inflammation levels in the body cannot be properly controlled. 

Without the influence of the vagus nerve pro-inflammatory cytokines are produced in much larger quantities in response to infection or injury. In certain conditions this can lead to dangerous levels of inflammation. 

Direct stimulation of the vagus nerve, either using electrical stimulation (tVNS or VNS) or natural stimulation methods, can trigger the release of anti-inflammatory markers that limit the production of inflammatory cytokines and over extended periods of consistent stimulation can help to lower the body’s setpoint equilibrium levels of inflammation. 

As Huston and Tracey write: “…advances in neuroscience have collided with this therapeutic approach, perhaps rendering possible the development of nerve stimulators to inhibit cytokines. Action potentials transmitted in the vagus nerve culminate in the release of acetylcholine that blocks cytokine production by cells…”