In this study, we discovered that patients with diabetes who were hospitalised because of COVID-19 had an increased risk of CVD incidence and all-cause mortality, as compared to those without COVID-19. Depending on the CVD subtype, CHD incidence and stroke incidence were significantly higher in patients hospitalised due to COVID-19 infection as well. From the results of subgroup analysis according to sex and age, patients with diabetes hospitalised due to COVID-19 showed a significantly higher risk of CVD and all-cause mortality than uninfected patients for all categories of subgroups, including men, women, middle-aged adults, and older adults. The risk of all-cause mortality in the middle-aged adults was significantly higher in patients with diabetes hospitalised because of COVID-19 than uninfected patients.
In a previous study, the results indicated that there was no statistically significant difference in risk of stroke and ischaemic heart disease between influenza-infected patients with diabetes and patients with diabetes hospitalised due to COVID-19 for both diabetes types 1 and 2; however, the risk of death was significantly higher in patients hospitalised for COVID-19. (20) We defined the control group as patients with diabetes but without COVID-19, and we showed that the risk of CVD incidence, including CHD and stroke, was increased in patients with diabetes hospitalised due to COVID-19. These results regarding the incidence of CVD could be due to differences in the definition of the control group.
Several previous studies have examined the association between diabetes and CVD, along with the relationship between COVID-19 and CVD. In a previous study, the risk of stroke increased in COVID-19 patients, and a link between severe COVID-19 and stroke incidence was reported. (4–8) These results suggest that the risk of stroke could be increased in patients with severe COVID-19 compared to uninfected individuals, especially those with known risk factors such as diabetes, which we discussed in this study. Another study that investigated the association between COVID-19 and CVD showed an increased risk of CVD, such as cerebrovascular disorders, myocarditis, and heart failure, 30 days after COVID-19 infection, indicating that follow-up management should be conducted in COVID-19 patients with cardiovascular disease. (8) Coagulopathy generally occurs in patients with severe COVID-19 and is associated with inflammatory reactions caused by the viral infection. It increases the risk of stroke, and cytokine responses due to an abnormal immune system can cause brain damage. In addition, the renin-angiotensin system, which is related to the regulation of the kidney, heart, and vascular physiology, is downregulated due to COVID-19, which can cause abnormalities in the function of organs such as the heart and brain. (4–8)
Diabetes is known to be a risk factor for mortality in COVID-19 patients, and our study observed an increased risk of all-cause mortality among patients with diabetes who were hospitalised due to COVID-19, as compared to those who were not infected COVID-19. (11–15) This could be due to reasons such as a weakened immune system, inflammation, and control of blood sugar. (11–15) From this perspective, our findings indicate that COVID-19 prevention and management are necessary to reduce mortality and CVD incidence in patients with diabetes.
This study had some limitations. First, our database contained no information on some parameters that affect the incidence of CVD and mortality, such as body mass index, smoking status, blood pressure level, and area of residence. Disease prognosis is often affected by health behaviours, including smoking and exercise, as well as medical accessibility such as income level and area of residence. Our findings are the results of not controlling for these factors. Second, we could not control for the vaccination effect, which affects the severity of the COVID-19 infection. Although we defined the control group as hospitalised patients with COVID-19 to reflect the severity of the COVID-19 infection, the vaccination status of every study participant was unknown and this may have affected the analysis results. Third, our database was limited to the Korean population. Further studies are needed to examine our findings in other countries and ethnic groups.