Infection can cause blood sugar levels to rise significantly even in individuals who do not have diabetes. This temporary metabolic shift is known as stress hyperglycemia. The body views any major illness, trauma, or surgery as a profound stressor, initiating a rapid and adaptive physiological response designed to provide immediate energy to fight the threat. While this blood sugar elevation is a normal part of the defense system, it can become problematic if glucose levels climb too high or persist for an extended period.
The Body’s Stress Response to Infection
Infection immediately mobilizes the immune system, requiring a massive and prompt supply of energy to fuel the inflammatory response. The body interprets this intense internal activity as a state of emergency, activating the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis, which together control the “fight or flight” mechanism. This neuroendocrine activation prepares the body for stress by signaling the need for available fuel. The resulting metabolic changes are a survival mechanism, ensuring that the brain and working muscles, including the immune cells, have a readily accessible source of glucose.
How Infection Directly Elevates Blood Glucose
The direct elevation of blood glucose is managed by a surge in counter-regulatory hormones. Primary among these are cortisol, epinephrine (adrenaline), and glucagon, all released in high concentrations during an infection. These hormones act as potent signals to the liver. Cortisol and glucagon compel the liver to increase glucose output through two separate processes. Glycogenolysis is the rapid breakdown of stored glycogen into glucose, while gluconeogenesis is the creation of new glucose molecules from non-carbohydrate sources, such as amino acids and fats. This dual action floods the bloodstream with glucose, providing the necessary energy for the immune system to function.
Simultaneously, the inflammatory state causes a temporary but significant state of insulin resistance throughout the body’s tissues. Pro-inflammatory molecules released by the immune system, such as cytokines like Interleukin-6 and TNF-α, interfere with insulin signaling at the cellular level. This means that the insulin produced by the pancreas cannot effectively unlock cells to take up the excess glucose from the blood. The combination of increased glucose production from the liver and impaired glucose uptake by the tissues results in a rapid and substantial spike in blood sugar, even in a non-diabetic individual.
Health Implications of Temporary Hyperglycemia
While temporary, high blood sugar levels can negatively affect the body’s ability to recover from illness. Elevated glucose can impair the function of immune cells, potentially slowing the body’s response to the invading pathogen. High blood sugar also reduces the efficiency of wound healing and tissue repair, which can complicate recovery. The kidneys attempt to flush the excess glucose from the bloodstream, a process that requires a large volume of water and results in frequent urination. This increased fluid loss can quickly lead to dehydration, especially if the person is also experiencing fever or reduced fluid intake due to illness. Maintaining adequate hydration is therefore an important part of managing the illness when blood sugar is elevated.
Monitoring and Resolution Post-Infection
For a non-diabetic person, stress hyperglycemia is generally transient and resolves as the underlying infection clears and the inflammatory response subsides. Once the stress hormones return to normal baseline levels, the liver reduces its glucose output and the body’s insulin sensitivity is restored. The blood glucose levels typically fall back into a healthy range without specific intervention. If high blood sugar readings persist after the illness has passed, or if the initial spike was extremely high, a doctor’s visit is advisable. Stress hyperglycemia can occasionally unmask undiagnosed pre-diabetes or new-onset Type 2 diabetes, as the extreme metabolic stress reveals a difficulty with glucose regulation. Monitoring after recovery can help determine if the high blood sugar was a temporary reaction to illness or a sign of a developing long-term metabolic condition.