The relationship between COVID-19 infection and metabolic health, particularly blood sugar control, is a significant area of research. The question of whether the virus causes lasting changes to a person’s average blood sugar, measured by the A1C test, is complex. Research suggests that while acute infection causes temporary spikes, the virus may also contribute to sustained changes that elevate A1C levels over time. Understanding this connection requires looking at both the short-term stress of the illness and potential long-term biological damage.
What A1C Measures
The A1C test provides a look at a person’s average blood sugar control over an extended period. Also known as the hemoglobin A1C or HbA1c test, it measures the percentage of hemoglobin in red blood cells that has glucose attached to it. Hemoglobin is the protein that transports oxygen throughout the body.
When sugar enters the bloodstream, it binds to hemoglobin in a process called glycation. The resulting molecule is stable for the lifespan of the red blood cell, which is about two to three months. A higher percentage of glycated hemoglobin indicates higher average blood sugar levels over that timeframe. For diagnosis, an A1C below 5.7% is normal, 5.7% to 6.4% indicates pre-diabetes, and 6.5% or higher signifies diabetes.
Short-Term Blood Sugar Spikes During Infection
Acute illness from COVID-19, particularly in severe cases, often leads to a temporary spike in blood glucose levels, even in people who have never had diabetes. This phenomenon, known as stress hyperglycemia, is a common response to any severe physical stressor or infection. The body reacts by releasing a flood of stress hormones, such as cortisol and adrenaline.
These hormones are counterregulatory, meaning they work against insulin, making the body temporarily insulin-resistant and increasing glucose production in the liver. Systemic inflammation caused by the virus also contributes to this resistance, worsening the body’s ability to move glucose out of the bloodstream and into cells. This acute elevation often resolves once the infection passes, but the short-term spike can contribute to a higher A1C reading if the test is performed shortly after recovery.
Link Between COVID-19 and Sustained Metabolic Changes
Beyond the temporary stress response, growing evidence suggests that COVID-19 infection can cause sustained metabolic dysfunction, leading to long-term A1C elevation or new-onset diabetes. One proposed mechanism involves the virus directly affecting the pancreas, the organ responsible for producing insulin. The SARS-CoV-2 virus uses the Angiotensin-Converting Enzyme 2 (ACE2) receptor to enter cells, and this receptor is expressed on the insulin-producing beta cells.
Direct viral infection of these beta cells may lead to their damage or destruction, reducing the body’s capacity to produce insulin and resulting in lasting hyperglycemia. Another element is the massive inflammatory response, often called a “cytokine storm,” which can trigger chronic, low-grade inflammation that persists after the acute infection clears. This persistent inflammation can worsen insulin resistance, compelling the pancreas to work harder. Research indicates that people who contract COVID-19 have an increased risk of developing diabetes compared to those who have not been infected.
Treatment and Recovery Factors Influencing A1C
Factors related to the treatment and recovery from a COVID-19 infection can also significantly impact A1C levels, independent of the virus’s direct biological effects. Corticosteroids like dexamethasone, a standard treatment for moderate to severe COVID-19, are known to sharply increase blood sugar. Glucocorticoids enhance the liver’s production of glucose and decrease the sensitivity of muscle and fat tissues to insulin, potentially leading to steroid-induced diabetes in some patients.
This medication-induced rise in blood glucose can be temporary while the patient is on the drug, but it contributes to a higher A1C reading if the hyperglycemia is severe or prolonged. The lengthy recovery associated with “Long COVID,” marked by persistent fatigue, reduced physical activity, and potential weight gain, can also contribute to worsening insulin resistance. Prolonged inactivity and altered diet can raise average blood sugar levels, increasing the A1C months after the initial viral clearance.