Have you noticed that cytokines have been in the news recently, and in particular "cytokine storms"? While the news stories have been about COVID-19, I think there could be a link to mental health. Let's look at what's been happening...

People who got COVID-19 and suffered really badly seemed to go into a cytokine storm where the body attacked the virus so viciously it did a lot of damage to itself.

The cytokine storm was a hyper-reaction to the presence of the virus. In fact, the reaction was so intense that it escaped the normal feedback mechanisms of the body and escalated until the people who experience it were actually in mortal danger from their own immune system.

The list of problems caused by a cytokine storm is extensive and frightening...

• Lungs: pneumonitis, pulmonary edema, dyspnea, hypoxemia, ARDS (Acute Respiratory Distress Syndrome)
• Liver: Hepatomegaly, elevated liver enzymes, increased hepcidin, hypoalbuminemia, liver injury, cholestasis, liver failure
• Kidneys: acute renal dysfunction or injury, renal failure
• Vascular and lymphatic systems: cytopenia, anemia, leukocytosis, coagulopathy, hyperferritinemia, elevated cytokines, endothelial damage and vascular permeability, capillary leak syndrome, vasodilatory shock, spontaneous hemorrhage, lymphadenopathy
• Nervous system: confusion, delirium, aphasia, seizures
• Constitutional symptoms: fever, anorexia, fatigue
• Heart: hypotension, tachycardia, cardiomyopathy
• Rheumatologic system: vasculitis, arthritis, arthralgia
• Gastrointestinal system: nausea, vomiting, diarrhea, ascites
• Skin: rash, edema

(list from Figure 1. Clinical Presentation of Cytokine Storm.)

But why did some people have such dramatic reactions to the SARS-CoV-2 virus and others not even know they were infected (asymptomatic)?

I think that's a fascinating question. It also strikes me as similar to why some people get fibromyalgia, chronic fatigue syndrome, myalgic encephalomyelitis, depression, anxiety, addictions and other physical / mental health conditions when others don't.

Sidebar: a quick word about whether a condition is "physical" or "mental": while some people would argue that the two are separate, I don't believe so. A physical issue, especially if it's chronic, can cause mental health problems. Someone suffering long-term pain may become less sociable, unhappy and eventually depressed. The depression would make their physical symptoms feel less manageable and make the situation seem worse, which starts a negative feedback loop. The brain, mind and body are all inter-linked. 

I think cytokines may be the answer, at least partially. Here's why...

The people who were most likely to need life support as a result of catching Covid were overweight and obese.

"This evidence suggests excess weight is associated with an increased risk of the following for COVID-19: a positive test, hospitalisation, advanced levels of treatment (including mechanical ventilation or admission to intensive or critical care) and death. The risks seem to increase progressively with increasing BMI above the healthy weight range, even after adjustment for potential confounding factors, including demographic and socio-economic
factors."
Public Health England, Excess Weight And Covid-19 PDF report.

One of the proposed reasons why people with obesity suffer worse outcomes from COVID-19 infection seems to be related to how adipose tissue affects the immune response...

"Obesity is known to induce a pro-inflammatory response, which has been
suggested to affect the performance of anti-viral treatment of influenza."
Public Health England, Excess Weight And Covid-19 PDF report.

I've already discussed in detail why I think being overweight or obese may contribute to mental health problems, and cytokines may be at the heart of the problem.

I'm not saying that being overweight/obese causes mental health issues, although it could very well contribute, I'm saying that obesity is a clue that dis-regulation of the immune system may be at the heart of mental health issues.

Another fact I found interesting was this...

"A few people who are diagnosed and treated for Lyme disease continue to have symptoms, like tiredness, aches and loss of energy, that can last for years. These symptoms are often compared to fibromyalgia and chronic fatigue syndrome. It's not clear why this happens to some people and not others. This means there's also no agreed treatment."
https://www.nhs.uk/conditions/lyme-disease/

Again we see some kind of dysregulation of the immune system causing long term suffering, and that suffering having a very similar profile to fibromyalgia, CMS/MS etc.

Now a picture is beginning to emerge...

A background level of chronic inflammation, either from being overweight/obese or some other mechanism (chronic physical pain, chronic mental stress/trauma), generates an on-going production of pro-inflammatory cytokines.

These cytokines act on the brain in various ways and can trigger the natural symptoms of "sickness", such as fatigue, pain, aches and loss of energy.

While those symptoms are normal during an acute infection, they are not normal when they become chronic and are labelled "fibromyalgia" or "chronic fatigue syndrome". Such level of background inflammation may make it more likely that the immune system, when presented with a new infection, reacts even more vigorously, potentially causing a cytokine storm as seen in COVID-19.

It would be interesting to know how severely sufferers of fibromyalgia, CMS/MS and similar conditions reacted to COVID-19.