Reasons for Morning Hyperglycemia

One of the most common question I hear from my clients is, "Why is my glucose high in the morning when I haven't eaten for hours?"

Maybe you can identify with this situation: You went to bed last night at 10:30 p.m. and your blood glucose was 126 mg/dL. When you woke up this morning at 6:00 a.m., it was 148 mg/dL.

What happened?

It's Probably Not Something You Ate

First, I want you to know that these circumstances aren't likely to be due to the dinner meal you ate the night before, or even to the ice cream you ate before going to bed. We know this is so because the rise in glucose caused by food is generally over within 2 to 5 hours after a meal, with this time range depending on the types of foods consumed. That is, a meal higher in fat will take longer to digest than if you ate only carbohydrates.

Other than illness and stress, possible reasons for these morning highs are

  • insufficient insulin
  • the dawn phenomenon
  • the Somogyi effect

Insufficient Insulin

If you take insulin, you might not be taking enough to cover your morning blood glucose levels. Try testing your blood glucose levels before bed and then again at around 2 a.m. If your blood glucose levels are high at 2 a.m., you might need more insulin. But be sure to talk with your doctor before making any of your own insulin adjustments.

The Dawn Phenomenon

This is defined as an early-morning rise in blood glucose levels due to the secretion of certain hormones--cortisol and growth hormone--that cause the body to release stored glucose. To determine if you are experiencing the dawn phenomenon, test your blood glucose level before bed and again at around 2 a.m. If your glucose is normal at 2 a.m. but high in the morning, you could be experiencing the dawn phenomenon. Ask your doctor about this.

The Somogyi Effect

This phenomenon is referred to as rebound hyperglycemia and is usually seen in people who take insulin. What happens is that blood glucose levels go too low late at night, which causes hormones to overcompensate by producing glucose. To determine if you are experiencing the Somogyi effect, try testing before you go to bed and again at 2 a.m. If your blood glucose levels are too low at 2 a.m. (less than 70 mg/dL is considered low), you might be experiencing the Somogyi effect. Again, let your doctor know. 

If you are experiencing morning highs, talk with your doctor or diabetes educator. Continuous glucose monitoring might be a good way to determine what is causing your morning hyperglycemia.

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