As the COVID-19 pandemic rages on worldwide, the common understanding is that people who have Type 2 diabetes are more likely to experience the severe symptoms of a COVID-19 infection, which can potentially be fatal to them.
The question is, though, how does Type 2 diabetes affect the immune system?
We tend to think of Type 2 diabetes as a lifestyle problem, and there are recommendations in place to consume less carbohydrates, exercise more, sleep better, and manage one’s stress better — all of which are contributors to a healthy immune system, too.
But let’s go into the science behind how Type 2 diabetes develops, and how it affects immune system responses. A deconstruction of this complicated process is necessary to understand how it works, and what one ought to be looking out for.
The curious case of insulin in the body
In a healthy human body, insulin is a biochemical that is produced from pancreatic beta cells and signals our cells to take in glucose from the blood at appropriate times. For the most part, each cell is obedient to the signal. Things work smoothly and are humming along. Blood glucose levels are well maintained at healthy levels — a more technical description of the entire process is found in this journal article here.
However, an unhealthy human body can be experiencing this situation known as insulin resistance.
Let’s create an analogy to understand insulin resistance better
In our younger years, most of us would have experienced the situation where our parents would tell us countless times to clean our rooms. Sometimes, we obey them and clean our rooms. At other times, we are preoccupied with doing other things (such as clearing the Big Boss level on our favourite video game, for instance), and as such, do not heed the parental orders to clean our rooms.
What if we were addicted to the game and never heeded the call of the parents to clean our rooms?
Would our parents not introduce more drastic responses, such as threatening us with grounding or taking away our video games? Would they not raise their voices (and perhaps their blood pressure too)?
What if we still refused to clean our rooms? Their responses would get even more drastic. Extreme anger can trigger heart attacks, which isn’t good for them either. They could possibly die from these extreme responses.
In the same way…
That is what is happening to our cells with insulin resistance. They resist the normal insulin signal that the beta cells are producing. As a result, the beta cells are called upon to produce even more insulin. However, if the resistance is not dealt with in time, the beta cells can die from overwork and still not be producing enough insulin. And when these beta cells die faster than they can be replaced, a Type 2 diabetes condition can be complicated into a Type 1 situation as well.
When our cells resist the insulin signal, they take in less glucose from the blood than necessary, which then results in a chronic accumulation of glucose in the blood over time. If that ain’t diabetes, I don’t know what you’re gonna call it!
Worse still, this glucose is reactive and can react with other biochemicals in the body in this chemical reaction known as glycation. Glycation is a common thing — most diabetics would have heard of the blood test that measures their HbA1c levels, for instance. What the HbA1c test does is that it determines how much haemoglobin (Hb) protein in our blood has been glycated by glucose into HbA1c. Hb is necessary for transporting oxygen through our blood to our cells — HbA1c cannot do that as effectively.
A higher HbA1c count indicates a reduced ability of our blood in transporting oxygen to our cells. Impaired oxygen supply down to our feet results in a poorer recovery from injuries, hence severely diabetic patients have to be extremely wary about foot injuries, because that could result in amputations for them.
The question is, what is causing our cells to resist the insulin signal in the first place?
This article indicates that an increased secretion of pro-inflammatory cytokines such as tumour necrosis factor alpha (TNF-α) and interleukin 1-beta (IL-1β) are responsible for triggering the insulin resistance problem. It is also possible that increased IL-1β levels also interfere with the beta cell ability to produce insulin. In fact, obesity can contribute further to insulin resistance as fat cells are known to aid in the production of IL-1β. This increased IL-1β production attracts the attention of the immune system’s macrophage cells:
This initial event may then lead to IL-1β-induced chemokines, resulting in the recruitment of macrophages. Subsequently, macrophage influx and activation within fat tissue may act as a prominent source of IL-1β secretion, triggering insulin resistance.
When the macrophages are involved in this activity (which is a vicious amplification loop where IL-1β is continuously being ramped up), their main role of “detecting, engulfing and destroying pathogens and apoptotic cells” is reduced, mainly because they are busy doing this other work of producing IL-1β. Part of the work that is conducted in the detecting, engulfing and destroying of pathogens and apoptotic cells includes the detecting, engulfing and destroying of virus-infected cells.
Does it now make more sense as to why people with pre-existing diabetes conditions are more susceptible to the effects of the COVID-19 coronavirus now? Their immune system responses to viral infections are suboptimal, and their clearance rates of virus-infected cells leave much to be desired, especially when their autophagy activity (which the macrophages contribute to) are dysregulated.
It’s always good to consume less sugar
A reduction in sugar intake may aid in the reduction of the insulin signalling intensity that is required for the cells to take in glucose. Let’s face it, though… We are constantly being bombarded by advertisements about processed foods that look oh-so-desirable. They appeal to our emotions. We consume them as “comfort foods”, and then an overconsumption of these things can lead to dire consequences down the road.
At the heart of the insulin resistance problem is the overproduction of pro-inflammatory cytokines. As inflammation is an immune system signal, it also follows that a dysregulated inflammation signal would lead to the dysregulation of immune system functions too.
Hence, diabetes (regardless of Type 1 or Type 2) is a big symptom of a poorly functioning immune system, as are other chronic inflammatory diseases where the inflammation signal is not being properly regulated.
Therefore it doesn’t really take a rocket scientist to figure out why a Type 2 diabetic is more susceptible to becoming a COVID-19 fatality.
But it does require some understanding of biochemical science to connect the dots!
Joel Yong, PhD, is a biochemical engineer/scientist, an educator and a writer. He has authored 5 ebooks (available on Amazon.com in Kindle format) and co-authored 6 journal articles in internationally peer-reviewed scientific journals. His main focus is on finding out the fundamentals of biochemical mechanisms in the body that the doctors don’t educate the lay people about, and will then proceed to deconstruct them for your understanding — as an educator should.
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