Apart from Dawn effect, a second possible cause of high blood sugar levels in the morning is the Somogyi effect, sometimes also called rebound hyperglycemia. It was named after the doctor who first wrote about it.
If your blood sugar drops too low in the middle of the night while you are sleeping, your body will release hormones in an attempt to “rescue” you from the dangerously low blood sugar. The hormones do this by prompting your liver to release stored glucose in larger amounts than usual. But this system isn’t perfect in a person with diabetes, so the liver releases more sugar than needed which leads to a high blood sugar level in the morning. This is the Somogyi effect.
How is it determined if the dawn phenomenon or Somogyi effect is causing the high blood sugar levels?
Your doctor will likely ask you to check your blood sugar levels between 2 a.m. and 3 a.m. for several nights in a row. If your blood sugar is consistently low during this time, the Somogyi effect is suspected. If the blood sugar is normal during this time period, the dawn phenomenon is more likely to be the cause.
Some additional clues that the Somogyi effect may be the cause include nightmares, restless sleep and overnight sweating as these are all signs of low blood sugar levels.