The connection between viral infection, particularly with SARS-CoV-2, and glucose metabolism is complex and often bidirectional. An active COVID-19 infection can significantly disrupt the body’s ability to regulate blood sugar, leading to temporary or lasting changes in metabolic health. This disruption can worsen existing diabetes or trigger new-onset diabetes in previously healthy people. Conversely, pre-existing high blood sugar levels substantially increase the potential for a severe course of the viral illness.
Acute Glucose Dysregulation During Illness
Active infection with SARS-CoV-2 often causes temporary high blood sugar, known as acute hyperglycemia, even in patients with no prior history of diabetes. This metabolic change results from the body’s systemic inflammatory response. The body releases high levels of stress hormones, specifically cortisol and adrenaline, to fight the virus.
These counter-regulatory hormones mobilize energy reserves by causing transient insulin resistance in the body’s tissues. Insulin resistance means cells become temporarily less responsive to insulin, the hormone responsible for allowing glucose to enter cells for energy. The resulting elevated blood glucose levels provide fuel for the immune system but can worsen the overall prognosis of the illness.
Inflammatory molecules, or cytokines, released during the infection also directly interfere with insulin signaling and action. This combination of stress hormones and inflammation causes the liver to produce more glucose than usual, while muscles and fat cells are less able to use it. For many individuals, this acute metabolic disturbance resolves once the infection clears.
COVID-19 as a Trigger for New Metabolic Conditions
A concerning long-term effect of the virus is the potential to trigger the onset of chronic diabetes (Type 1 or Type 2) in individuals who were metabolically healthy before infection. The virus gains entry into human cells by binding to the Angiotensin-Converting Enzyme 2 (ACE2) receptor, which is abundant throughout the body. The ACE2 receptor is also found on the beta cells in the pancreas, the cells responsible for producing insulin.
This suggests a pathway through which the virus may directly invade or damage the insulin-producing beta cells. Direct viral replication could lead to their destruction, permanently impairing insulin production, which is the hallmark of Type 1 diabetes. Additionally, the intense systemic inflammation caused by the virus can indirectly damage pancreatic function or severely compromise insulin sensitivity, a mechanism seen in Type 2 diabetes development.
Studies indicate that individuals recovered from COVID-19 have an elevated risk of being diagnosed with new-onset diabetes compared to non-infected individuals. This new condition may result from acute stress-induced hyperglycemia failing to resolve, or from the virus initiating an autoimmune response targeting pancreatic cells. The evidence suggests that SARS-CoV-2 infection can leave a lasting imprint on glucose regulation.
The Impact of Existing Diabetes on Viral Severity
The relationship between COVID-19 and blood sugar is bidirectional, as pre-existing diabetes significantly influences the course and severity of the viral infection. Individuals who manage diabetes, especially with poor blood sugar control, face a substantially higher risk of severe illness, hospitalization, and increased mortality from COVID-19. Research indicates that pre-existing diabetes is associated with an approximate twofold higher risk of severe illness and a three-fold increased risk of in-hospital mortality.
Chronic high blood sugar impairs the immune system, making it less effective at fighting the viral threat. Uncontrolled glucose levels promote chronic, low-grade inflammation and a pro-coagulant state. This contributes to the harmful blood clots and widespread inflammation characteristic of severe COVID-19, predisposing the patient to worse outcomes, including acute respiratory distress syndrome.
Diabetes often comes with other related health problems, such as high blood pressure and heart disease, which are themselves risk factors for severe COVID-19. When a diabetic patient becomes ill, the stress of the infection can cause blood sugars to spike dangerously high. This can precipitate serious complications like Diabetic Ketoacidosis (DKA), further worsening the prognosis. Maintaining optimal glycemic control is a powerful protective measure against severe outcomes.
Practical Steps for Monitoring Blood Sugar
Individuals with diabetes must maintain heightened vigilance regarding blood sugar control during and after any illness, including COVID-19. Diabetic patients should have a “sick day plan” established with their healthcare team, including guidance on medication adjustments and increased monitoring frequency. They should check their blood glucose more frequently than usual, even if eating less, and should not stop taking insulin or other prescribed medications without medical advice.
Monitoring for signs of hyperglycemia and DKA is necessary, especially for those with Type 1 diabetes. Symptoms include frequent urination, excessive thirst, nausea, or abdominal pain. For non-diabetic individuals who experienced acute hyperglycemia during the infection, or those with risk factors like prediabetes, follow up with a physician for metabolic screening post-recovery is advisable. This screening should include checking hemoglobin A1c (HbA1c) levels to determine if the acute glucose disruption has transitioned into a chronic condition.