New Study Shows Covid-19 Risk Higher in Type 2 Diabetes than Type 1


A new study of people with diabetes hospitalized with COVID-19 has found that Type 1 diabetes may be significantly less dangerous than Type 2 diabetes.

The paper, titled “Type 1 Diabetes in People Hospitalized for COVID-19: New Insights From the CORONADO Study” (PDF), analyzed hospital admissions in France during the final weeks of March, around the time when COVID-19 infections appeared to peak in that country. Researchers identified 2,608 patients with some form of diabetes, of whom 56 patients (2.1%) were found to have Type 1 diabetes.

That number was surprisingly low, suggesting that people with Type 1 diabetes (T1D) are comparatively underrepresented among people with diabetes that the novel coronavirus made ill enough to require hospital admission. Epidemiological studies have shown that 5.6% of people with diabetes in France have Type 1 (the CDC reports a similar ratio in America). And the risk of death for patients with T1D was only half that of patients with T2D.

Ever since the earliest days of the pandemic it has been known that people with “diabetes” were more likely to suffer severe illness and death from COVID-19. For months, however, the precise risk to people with Type 1 diabetes has been far less certain. The most comprehensive study to date, by scientists associated with the United Kingdom’s National Health Service, found that people with Type 1 were at a somewhat higher risk of death than those with Type 2.

The CORONADO Study was a major effort to study people with diabetes, encompassing data from 53 different French health centers. Initial analysis of the CORONADO data, published in May, showed that the overwhelming majority of those patients had Type 2 diabetes—only 3% were identified as patients with Type 1. At that time, the study designers did not analyze the Type 1 results in detail, but a cursory discussion of the topic was optimistic: “our data can be considered reassuring for the majority of people living with type 1 diabetes.” The study found no instances of death “in participants with type 1 diabetes younger than 65 years.”

Now that the researchers have taken a closer look at the data, their conclusions remain largely the same. Remarkably, only one single clinical characteristic was found to be strongly correlated with severe COVID-19 outcomes (tracheal intubation and/or death): advanced age. Of the patients with Type 1 diabetes over the age of 74, 50% died or were intubated. By contrast, only 12% of T1D patients under the age of 55 were intubated, and zero died.

Two of the missing correlations were striking. Contrary to expectations, T1D patients that experienced severe negative outcomes were not significantly heavier than those that did not, as measured by either BMI or obesity prevalence. And perhaps most surprisingly, doctors found no correlation between blood sugar control and outcomes. (In fact, those most severely afflicted actually exhibited superior blood sugar control, but not to a statistically significant degree). We have previously reported that blood sugar control appears to be a highly meaningful factor in the progress of the disease caused by the novel coronavirus (“COVID-19: Why Blood Sugar Matters”).

It is likely that the lack of other identifiable risk factors is an artifact of the small size of the study. While the 13 patients that experienced death and/or intubation were more likely to suffer from comorbidities such as hypertension and long-term diabetes complications, and were more heavily medicated, the sample was just too small for any of those correlations to achieve statistical significance.

While we obviously need to take these results with a grain of salt, the study can be considered another piece of evidence that even for people with Type 1 diabetes, advanced age remains probably the single most significant risk factor. Even the United Kingdom study, which did show a dramatically increased risk of death among those with T1D, also found that younger people with Type 1 diabetes were relatively safe: in a much larger sample, deaths under the age of 49 were so rare that the exact number was suppressed due to government privacy regulations.

It is possible that the CORONADO Study, while comparatively small, more accurately identified patients with Type 1 diabetes than did the United Kingdom study, which has been criticized for potential categorization errors. Even at the best of times, it can be difficult to distinguish between Type 1 and Type 2. The UK registry appears to categorize 7.7% of people with diabetes as having T1D, compared to France’s 5.6%, which could indicate a truly different prevalence or more expansive standards for defining “Type 1.” The CORONADO researchers also appear to have applied an extra measure of rigor in their attempt to accurately identify Type 1 diabetes status: all cases noted as T1D were carefully reviewed by local investigators,” and diabetes classifications for many were “systematically reviewed.” In addition, the study excluded patients that were diagnosed with diabetes upon admission with COVID-19, a phenomenon of shocking frequency that probably doesn’t shed much light on the odds of people with long-term diabetes.

It is important to remember that the new CORONADO study doesn’t compare T1D outcomes to those of people without diabetes. People with Type 1 diabetes still must be considered “higher risk” individuals. Nevertheless, we can hope that the new study accurately identifies that the risk to people with T1D is somewhat less than the very high risks to people with T2D, which by now are unfortunately beyond dispute.

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