High blood sugar in the morning is often caused by natural hormone changes that happen before you wake up. This is known as the dawn phenomenon. It can also occur if there is not enough insulin working overnight or if blood sugar was already elevated at bedtime.
In the early morning hours, hormones like cortisol and growth hormone rise. These hormones signal the liver to release more glucose into the bloodstream. If insulin levels are not sufficient to balance this increase, blood sugar may be high upon waking. High blood sugar in the morning caused by your blood sugar dropping too low overnight, sometimes called the Somogyi effect, seems to be less common than doctors once believed.
Late or high-carbohydrate evening meals can also raise fasting glucose levels. Poor sleep quality has been linked to stronger early-morning glucose rises in people with type 2 diabetes. Checking bedtime, overnight, and morning readings can help identify the pattern.
Do not adjust insulin or other diabetes medications on your own. A primary care doctor or endocrinologist can review your glucose trends and make safe treatment changes if needed.