Why does my blood sugar go up when I'm sick?

Your blood sugar rises when you are sick because the body secretes of variety of hormone and other substances in the process of fighting infection that either raise blood sugar directly or make the body resistant to the actions of insulin. Cortisol is the body’s main “stress” hormone, and cortisol makes the body more resistant to insulin action. In other words, insulin will not lower blood sugar as well in the presence of high levels of cortisol as it does when cortisol levels are lower. This is the same reason that man-made anti-inflammatory steroids, like prednisone, which are all patterned after cortisol, will raise blood sugar. Many people who have autoimmune or inflammatory disorders will see a dramatic rise in their blood sugars when they are given prednisone. Other hormones, like adrenaline (also called epinephrine) will cause the liver to release glucose directly into the bloodstream. This is why certain asthma medications which mimic adrenaline action (a common example being albuterol) will also raise blood sugar levels.

Think of the person who has diabetes and asthma who gets pneumonia which is severe enough to require hospitalization. Between the body’s rise in cortisol and adrenaline, and the administration of large doses of prednisone and albuterol to combat airway constriction, you can see how complex the interactions become in treating diabetes in combination with other medical problems!