Low-grade chronic, systemic inflammation caused by high levels of circulating cytokines is an emerging factor in crossover studies of depression, anxiety, metabolic disorders, autoimmune disorders, and rheumatoid arthritis [38]. A cytokine is a small protein released by cells that has a specific effect on the interactions between cells [40]. Cytokines influence brain neurotransmitters that either affect the brain positively (brain plasticity) or negatively (pro-inflammatory) in the HPA axis [38. 40]. (Brian doesn’t like pro-inflammatory cytokines).

Stress (anxiety) and depression are both associated with activation of our immune system. Activation of this system is helpful in terms of fighting off germs and viruses however if the immune system is constantly inflamed due to chronic stress, our anti-inflammatory response diminishes and leaves us vulnerable to continual infections, and diseases. When inflammation is persistent, it causes an increase in production of inflammatory cytokines [38, 40].

Increased cytokines interfere with tryptophan availability which reduces the production, release, and synaptic brain uptake of serotonin. From what we discussed earlier, this further explains how serotonin activity is diminished and leads to the development of depression [40].

Clinical studies confirm this research. When certain cytokines are administered to patients, they deplete available serotonin and typical symptoms of depression and increased anxiety emerge. High levels of inflammation not only cause mitochondrial dysfunction but can also change thoughts, emotions, motivations and behaviors. For example, when we have a viral infection we generally become lethargic, unmotivated and want to just stay I bed [111]. This is a perfectly normal response, as resting allows for the conservation of resources that the body needs for survival and recovery.

On a positive note, the Mediterranean and plant-based eating styles seem promising for alleviating and recovering from many of the symptoms of chronic inflammation.