The Type 1 diabetes online community was abuzz this week when an article from the journal Medical Hypotheses went viral. The article, authored by four Italian doctors, wonders if people with Type 1 diabetes are unusually resistant to Covid-19: Is it fair to hope that patients with Type 1 Diabetes (autoimmune) may be spared by the infection of Covid-19?
The Italian theory, as I will hereafter refer to it, wondered if people with Type 1 diabetes were experiencing a “milder course” of Covid-19 due to the unique details of their autoimmune dysfunction. Type 1 diabetes is often characterized by an imbalance of T helper cells, specifically an overabundant or overactive population of Th1 cells, which contributes to the condition’s defining Beta cell destruction. According to the authors, TH1 may be one of the body’s most effective defenses against the novel coronavirus, an unexpected silver lining for a dangerously overcharged immune system.
While many in the community happily latched onto this optimistic theory, those with a critical eye quickly found reasons to dismiss it. For one thing, the paper was submitted in early April, which was a veritable epoch ago, given how much more data we now have on the coronavirus. It seemed to rely mostly on anecdote rather than data. And the theory itself was hardly couched in the most confident of terms; it was clearly just a hypothesis that needed testing.
Perhaps most significantly, the hypothesis was directly contradicted by what is (to our knowledge) the best single analysis of the outcomes of people with Type 1 diabetes that have contracted Covid-19. In May, two papers from the United Kingdom’s National Health Service (NHS) analyzed thousands of hospital admissions to estimate the mortality of Covid-19 patients with diabetes, separately considering Types 1 and 2. The bottom line wasn’t good. As we summarized at the time, the UK data showed that people with Type 1 diabetes appeared to be roughly 3 times as likely to die of COVID-19 as those without diabetes.
It seems clear that the NHS analysis, based on a strong data set, should supersede speculation from a month previous. When I contacted Dr. Partha Kar, one of the authors of the NHS analysis, he described the Italian theory as “speculative nonsense.” A reddit thread on the Italian theory was eventually locked by moderators and stamped with an “outdated” tag.
The Authors Speak
I wondered: did the authors of the theory recognize their own hypothesis as outdated, or as supplanted by newer data? So I reached out to them.
Lead author Dr. Patrizio Tatti, representing his colleagues, told me that “We see no reason to change our opinion.”
Dr. Tatti emphasized that his team’s hypothesis covered only a very specific population: people with autoimmune Type 1 diabetes without other comorbidities under the age of 40. Readers could be forgiven for misunderstanding the scope of the theory, as these limitations were not set forth in the online versions of the article published by Medical Hypotheses.
The evidence for the Italian theory was not entirely anecdotal. The four Italian authors referred to data sets from both Italy and China, in addition to anecdotal information, including March reporting from the International Society for Pediatric and Adolescent Diabetes. (The Italian data actually prompted speculation from an entirely different group of Italian doctors, who came up with a different theory for why Type 1 patients seemed to be unaffected by Covid-19. Yet with only 1,591 patients analyzed, it seems obvious that the sample was far too small to draw any conclusions about Type 1 diabetes, a fairly rare condition.)
Dr. Tatti further explained that he suspected that the NHS study out of the UK may have been tainted by miscategorization: “many patients with Type 2 diabetes may have been shifted during the course of their disease into the T1 diabetes category, at a time when insulin treatment was initiated.” He pointed to the average age of those with apparent Type 1 who had died, 72.2, as an indication that this had likely occurred.
When I asked NHS’ Dr. Partha Kar whether or not his team’s data could have been marred by the inclusion of many patients with non-autoimmune diabetes, he acknowledged that proper categorization and diagnosis can be an issue. But he reiterated that he was confident in the quality of the NHS data, in his words “perhaps the most validated database around,” and that his team’s conclusions were “robust enough to suggest that [people with Type 1 diabetes] need priority in vaccination.”
In Dr. Tatti’s telling, the analysis performed by the NHS actually supports his hypothesis that autoimmune Type 1 diabetes can provide a “defensive effect,” at least in the absence of comorbidities. In the NHS data, deaths among T1D’s under the age of 50 were rare enough that the exact numbers were suppressed due to privacy concerns. The authors of the NHS analysis stated that “even with the additional risk associated with Type 1 diabetes or Type 2 diabetes, people under the age of 40 years with either type of diabetes were at very low absolute risk of in-hospital death with COVID-19.”
Could Type 1 diabetes create a “defensive effect” against the new coronavirus in young and otherwise healthy people? It’s impossible to say. While the NHS study certainly was not designed to ask this question, Dr. Tatti’s work remains highly speculative. Perhaps future study will show us for sure, or a successful vaccine will render the question irrelevant. But in the humble opinion of this writer, banking on a “defensive effect” seems like a dangerous type of wishful thinking.