Why even mild cases of Covid increase the risk of diabetes

For Eurípedes Donizeti Donzeli, 66, Covid came in a double dose: in February 2021, he was diagnosed with the disease for the first time. Ten months later, a new test confirmed that he had coronavirus again.

“In both situations, I didn’t have any symptoms. In the first episode, I only took the exam because my wife had a fever. In the second, I participated in an end-of-year get-together and discovered that some people present had tested positive”, reports the resident. de Franca, in the interior of São Paulo.

But the surprises didn’t stop there: after recovering from the second frame of Covid, Donzeli was guided by the doctor to do some routine exams, the popular check-up. “That’s when I found out my glucose was at 146 and I was diagnosed with diabetes afterwards,” he says.

Ideally, glucose should be below 100 milligrams per deciliter (mg/dl) of blood when fasting.

“I had no family history of diabetes and I didn’t expect this one now,” he continues.

And donzeli’s story is far from a rarity: research carried out in recent months shows that endocrinologists should add Covid-19 as a new risk factor for diabetes.

The latest study to prove a link between coronavirus infection and the later development of this disease, marked by uncontrolled glucose levels, was recently published in the specialized journal The Lancet Diabetes & Endocrinology.

In it, scientists at the St. Louis and Washington University, in the United States, compared the data of 181,000 individuals who had Covid between March 2020 and September 2021 with those of 8 million people who did not become infected with the coronavirus in the same period.

The difference with this investigation is that the researchers had already compiled the health information of all these participants between 2018 and 2019, before the pandemic started. In practice, this allowed estimating how many cases of diabetes were expected each new season – and how Covid-19 influenced this scenario.

In summary, the results show a 40% increase in the risk of diabetes among those who have been infected by the coronavirus. Of every 100 participants who caught Covid, two had the endocrinological disease soon after.

Dr Ziyad Al-Aly, lead author of the research, says he was surprised to find that this risk was seen even in people who had no other risk factors for developing diabetes, such as obesity, cardiovascular disease or a family history.

“Another thing we didn’t expect is that the disease can appear even in patients with asymptomatic or mild cases of Covid-19”, he tells BBC News Brasil.

It is worth noting that, in the study in question, the risk of having diabetes was higher in the most severe cases of infection, but this relationship was also observed in individuals who caught the coronavirus and did not develop such serious discomfort.

Doctor Hermelinda Pedrosa, former president of the Diabetes Department of the Brazilian Society of Endocrinology and Metabology, who did not participate in the American study, believes that the results obtained are even sufficient to face Covid-19 as an additional risk factor for diabetes.

“These data come from a job very well done, with a robust methodology and a comparison that took into account the pre-pandemic history and the diagnosis of Covid”, he praises.

“People who have had Covid should be aware and eventually even undergo a medical evaluation, especially if they already have obesity, hypertension, high cholesterol, cardiovascular diseases or have a family history of diabetes”, guides the endocrinologist, who also coordinates one of the centers of research at the Taguatinga Regional Hospital, in the Federal District.

Many suspicions, few definitions

First of all, it must be made clear that these studies linking Covid and diabetes are observational and do not allow a cause and effect relationship to be established.

Translation: what these surveys do is check what happened to a certain group of people after an event or an intervention.

In the specific case of this American research, the objective was to verify if there was and what was the risk of diabetes after Covid.

Even confirming that there is something that links the two phenomena, this model is not able to explain the mechanisms behind this relationship. Therefore, everything you will read in the next paragraphs must be seen as a possibility, which still lacks more scientific evidence.

“There are a number of hypotheses to explain this increased risk, including the persistence of the coronavirus in the body, which can cause a chronic inflammation behind the decrease in insulin sensitivity”, suggests Al-Aly.

Insulin, cited by the doctor, is the hormone produced by the pancreas that has a primary function for the functioning of our body: allowing glucose (a type of sugar, obtained through food) to enter each cell of the body, where it will be used as a source of energy.

If there is a problem with the functioning of the pancreas, or if the insulin stops working as expected, the glucose is “stranded” in the blood. This imbalance in the amounts of sugar in the bloodstream causes a number of health problems. We are talking here about a classic picture of diabetes.

Endocrinologist Carlos Eduardo Barra Couri, a researcher at the University of São Paulo in Ribeirão Preto, draws attention to other possible explanations for the likely link between Covid and diabetes.

“In addition to the inflammation of Covid itself leading to an increase in insulin resistance, the treatment of severe cases of infection involves the use of corticosteroids, anti-inflammatory drugs that increase the risk of diabetes”, he recalls.

“There is also a possibility that the coronavirus will directly attack the pancreas, but this is still speculation.”

“Although the exact mechanism is not yet known, we know very well that Sars-CoV-2, the cause of Covid, is far from being a virus that only affects the respiratory system”, completes the specialist.

Endocrinologist Denise Franco, who is a member of the board of the Brazilian Society of Diabetes, believes that the coronavirus infection would act as a kind of “drop of water”, the last element that was missing for insulin resistance to show up.

“It is as if the patient already had a series of risk factors for diabetes, such as overweight, obesity and sedentary lifestyle, among others, and the inflammatory condition of Covid acted as a final trigger for the development of the disease”, he interprets.

So what to do?

As science advances and tries to understand the details of this unusual relationship, doctors already have some recommendations for those people who have had Covid and are concerned about glucose balance.

The first, of course, is to seek a medical evaluation and check if there is a need to perform tests to diagnose (or rule out) diabetes.

“In short, it is possible to measure fasting blood glucose, glycated hemoglobin or do the oral glucose tolerance test”, lists Couri.

“We are talking about simple and easily accessible tests”, adds the doctor.

There is still no clear guidance on whether everyone who has had Covid really needs to go through a check up of the type, but the experts heard by BBC News Brazil think that at least those who already have other risk factors should take these tests. This includes patients with a family history of diabetes, the elderly, obese or overweight individuals, hypertensive individuals and those with other cardiovascular diseases.

“People with pre-diabetes, when the blood glucose is between 100 and 125 mg/dl, should also be careful”, adds Pedrosa.

It is worth remembering here that diabetes is a silent disease, in which the typical symptoms (excessive thirst, a lot of urge to pee, weight loss…) are very subtle or only show up at a later stage.

If the diagnosis is confirmed, the treatment of diabetes follows what endocrinologists usually prescribe for cases where there is no relationship with Covid.

“It is up to each professional to identify whether it is type 1 or 2 diabetes and indicate therapies to control the condition”, informs Couri.

Type 1 diabetes is an autoimmune disease, in which the body’s own cells attack the pancreas, which struggles to manufacture insulin.

Type 2 begins with insulin resistance: the hormone is there, but it can no longer get glucose into the cells. As the condition progresses, there may also be an exhaustion of the pancreas itself.

To close, there is one last mystery that surrounds the relationship between Covid and diabetes. Could it be that, in these more recent cases, the lack of control of blood glucose levels is transitory and will it resolve naturally after some time? Or will patients live with this problem for the rest of their lives?

“The most honest answer we can give now is that we just don’t know,” Couri replies.

“I prefer to wait for long-term studies to understand if this diabetes condition is a transient sequel or if it was anticipated by Covid and is here to stay”, he adds.

Al-Aly points out that his research has some limitations, such as the fact that it only included US war veterans and had a limited twelve-month follow-up. “We still don’t have a full understanding of what can happen after a year. [após a recuperação da Covid]”, he ponders.

“We also need to understand what effect Covid vaccination can have on these long-term post-Covid manifestations,” he says.

“That’s exactly what we’re doing now: check the impact of immunizations in this scenario, follow patients for two years or more and understand the type of diabetes that is affecting these individuals and the best ways to treat them”, concludes the doctor.

According to the International Diabetes Federation, approximately 537 million adults have the disease worldwide, a number that is expected to increase to 643 million in 2030 and jump to 783 million in 2045.