Why Blood Sugar Can Be High in the Morning

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Serene man sleeping in bed in the morning

You wouldn’t expect hours of sleep and fasting to leave you with high blood sugar. But elevated morning glucose may be more common than you think. Although it’s not a major problem when it occurs from time to time, consistently high morning levels need your doctor’s attention.

Causes of Morning Hyperglycemia

High blood glucose in the morning typically occurs due to one of three distinct causes:  

Dawn Phenomenon

The “dawn phenomenon” describes high morning glucose that occurs due to a natural rise in hormone levels. During the early morning hours between about 4 and 8 a.m., your body releases hormones like cortisol and growth hormones to get ready for the day. For reasons experts don’t completely understand, your liver produces extra glucose in response to these hormones. People without diabetes secrete more insulin to handle the extra glucose. But for people with diabetes, blood glucose levels can rise too high.

Increased blood sugar due to the dawn phenomenon is usually treated with diabetes medication. If you are on insulin, your insulin levels may need to be changed.

The Somogyi Effect

It’s possible to experience low blood sugar, or hypoglycemia, while sleeping and not even know it. The potentially dangerous problem can occur for a number of different reasons—from not eating enough or taking too much insulin, to drinking too much alcohol. In some people, the body compensates for the hypoglycemia by producing a lot of hormones. This, in turn, causes blood sugar levels to rise.    

Not everyone wakes in reaction to low blood glucose levels. But being sweaty or having a headache in the morning can be a sign. If you suffer from the Somogyi effect (named after the scientist who first described the condition), your doctor may recommend that you eat a snack before bed or reduce your insulin at night.

Waning Insulin

If you take insulin and have been experiencing high blood sugar in the morning, your insulin may simply be wearing off too soon. If this is the case, your doctor can adjust your dosage or change what time you are taking the insulin to prevent high glucose levels.

Pinpointing the Cause for Effective Treatment

It’s important to understand what’s causing your morning hyperglycemia before your doctor can treat you. To pinpoint which of the three reasons is behind your high numbers, check and record your blood glucose before you go to bed, at 3 a.m., and then first thing in the morning. Although it isn’t fun to set a middle-of-the-night alarm, continue to do so for a few nights in a row.

If your blood sugar is fairly even when you go to bed and at 3 a.m. but is higher in the morning, you are probably experiencing dawn phenomenon. If your blood sugar is low at 3 a.m., but high in the morning, you probably suffer from the Somogyi effect. If your blood sugar is elevated at 3 a.m. and then higher still in the morning, you probably have waning insulin.

Even if you’ve identified the reason behind your high morning number, never attempt to correct it on your own. Instead, talk with your doctor. Together, you can find a treatment plan that gets you back on track in the morning.

Key Takeaways:

  • High blood sugar in the morning is typically caused by the dawn phenomenon, the Somogyi effect, or waning insulin.

  • To pinpoint what’s behind your high numbers, check and record your blood glucose before you go to bed, at 3 a.m., and first thing in the morning.

  • Never attempt to correct the problem on your own; instead, talk with your doctor.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2019 Jul 20
Why is my blood sugar so high in the morning? American Diabetes Association. http://forecast.diabetes.org/magazine/ask-experts/why-my-blood-glucose-so-high-morning
Rocky Morning Highs? American Diabetes Association. http://forecast.diabetes.org/magazine/features/rocky-morning-highs

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