This study analyzed clinical data from a global registry of 795 cases of diabetes associated with COVID-19, including 537 cases of newly diagnosed diabetes and 258 cases of acute metabolic complications of pre-existing diabetes. We specifically assessed cases of newly diagnosed diabetes for evidence of new onset of the disease in close temporal relationship with the episode of COVID-19. The results of this analysis provide clinical plausibility for a diabetogenic effect of COVID-19.
In this study, most patients who received a new diagnosis of diabetes in association with COVID-19 exhibited levels of HbA1c above thresholds used for diabetes diagnosis at presentation, suggesting that diabetes likely preceded the infection. This finding is not surprising, considering that about 46% of all global cases of diabetes in adults are undiagnosed.14
However, our study also shows that newly diagnosed diabetes associated to COVID-19 cannot be entirely explained by pre-existing disease. In fact, we were able to verify new-onset diabetes in at least 102 cases of newly diagnosed cases associated with COVID-19. These patients exhibited glycemic levels above thresholds for diagnosis of diabetes with HbA1c levels still in the non-diabetic range, consistent with onset of hyperglycemia during SARS-CoV-2 infection.
We have also documented persistence of hyperglycemia beyond the resolution of COVID-19 in at least 39 cases of new-onset diabetes with follow-up data available (45%).
We acknowledge that HbA1c levels above 6·5% at time of diagnosis may still be compatible with new-onset diabetes. Our strict definition of “new onset-diabetes” in this study may therefore underestimate the phenomenon; however, this approach reduces the likelihood of pre-existing disease. On the other hand, HbA1c between 6·0% and 6·5% could indicate that a state of pre-diabetes preceded the infection. However, acute progression from pre-diabetes to diabetes would still suggest a negative effect of COVID-19 on glucose metabolism.
In the aggregate, these results provide evidence of clinically relevant alterations of glucose metabolism acutely occurring with COVID-19 infection. Although these data do not prove that SARS-CoV-2 causes diabetes, the findings are the most meaningful clinical evidence to date in support of a possible diabetogenic effect of SARS-CoV-2. Confirmation of a cause-effect relationship between COVID-19 and diabetes will require further, consistent, and complementary evidence from epidemiologic, biologic, and clinical investigations.
While a potential viral etiology has been generally associated with T1D,22 our study shows that T2D is the dominant subtype among patients with new-onset diabetes in the acute phase of COVID-19. This finding is consistent with other reports showing that T2D also accounts for the majority of newly diagnosed cases of diabetes associated with the post-acute phase of COVID-19.8,9,11,12
Also, a small clinical study using continuous glucose monitoring and hormone level assessment documented various alterations of glucose metabolism, including dysglycemia, insulin resistance and abnormal cytokine profile in association with COVID-19 infection, resembling pathophysiologic characteristics of T2D.23
These observations suggest a complex pathophysiology, consistent with evidence that SARS-CoV-2 can infect not only the pancreas16–18 but also other metabolic organs such as the adipose tissue, the liver and the small intestine.19,20
The association between COVID-19 and T2D in this and other studies raises the intriguing hypothesis that other viruses, globally endemic over the last several decades, may have contributed to the recent epidemic of T2D. Although the hypothesis needs verification, it may provide new impetus and direction for the search of the elusive cause of T2D and the understanding of its pathophysiology.
Our analysis could only rule out pre-existing disease in two pediatric cases and one adult case of newly diagnosed T1D. However, we cannot exclude that this subtype may develop more often in association with COVID-19. In fact, definitive diagnosis of diabetes subtype was not feasible or available in 41% of adult cases with new-onset diabetes in this series. Moreover, this study was not designed to look at potential long-term consequences of COVID-19 on diabetes. Despite such caveats, our findings seem reassuring in regard to the previously hypothesized risk that COVID-19 may induce a large, epidemic wave of T1D.8,24
Stress-induced, temporary hyperglycemia can occur with acute illnesses or corticosteroid therapy, especially pneumonia, both inherently associated with COVID-19.14,25 It is therefore not possible to rule out that stress hyperglycemia might explain at least some of the observations of new-onset diabetes associated with an acute episode of COVID-19. In this study, however, hyperglycemia persisted beyond the acute episode of COVID-19 in about half (45%) of all cases of new-onset diabetes and durability of diabetes was documented for at least three months in more than 80% of cases where hyperglycemia survived the infection. These data suggest that COVID-19 can induce durable alterations of glucose metabolism. Our results are consistent with reports of persistent hyperglycemia in patients with newly diagnosed diabetes occurring during or after COVID-197,11,12 as well as with findings from other studies showing sustained alterations of glucose metabolism even in patients who do not develop diabetes during COVID-19.23
Although about half (55%) of patients with new-onset diabetes in this study experienced remission of hyperglycaemia with the resolution of the infection, it remains unclear if these patients remain at risk of disease recurrence or development of new diabetes in the future, similarly to gestational diabetes.
Altogether, these observations warrant follow-up studies to understand the evolution of diabetes and the risk of future diabetes after COVID-19.
There are several strengths of this study. By collecting data of clinical observations of new-onset diabetes associated with COVID-19 from 25 countries, our study confirms this phenomenon across multiple world’s regions and ethnicities. The global outreach of CoviDIAB also allowed us to gather the largest series of clinically documented new-onset diabetes associated with COVID-19 or any viral infection to date. Furthermore, the close temporal association between SARS-CoV-2 infection and the onset of diabetes in this series makes the study more relevant for inference of cause-effect relationship.
This study has several limitations. As an international registry that relies on voluntary contribution from clinicians across many hospitals and countries, CoviDIAB data inherently reflect heterogeneity in practice and clinical judgement of contributing clinicians. Information about pathophysiology (e.g., C-peptide, antibodies, etc.) is limited, since these tests are not part of standard clinical practice in many countries. Hence, we could not independently confirm assessment of diabetes subtypes and must rely on clinical assessment by contributing clinicians.
Our follow-up data are also still limited. Most of the observations in this study relate to earlier phases of the pandemic and may not reflect effects of newer variants of SARS-CoV-2.
In conclusion, our study provides clinical plausibility for a diabetogenic effect of SARS-CoV-2. This finding warrants further research to confirm a possible etiologic role of SARS-CoV-2 in diabetes and to investigate the mechanisms of viral interference in glucose metabolism. Our data support screening for diabetes during the acute and post-acute phase of COVID-19.