Blood sugar can go up at night for various reasons in people with diabetes. One potential reason is a drop in insulin.

If a person’s insulin pump does not provide enough background insulin overnight, or their long-acting insulin dose is too low or used too early, the levels may drop during sleep. This causes blood sugar levels to rise.

Blood sugar levels can also increase in the early hours of the morning due to the dawn phenomenon, which is a surge in hormones that helps the body wake up.

Hormones such as cortisol and growth hormone signal the liver to release glucose, providing the body with energy. However, in people with either type of diabetes, a lack of insulin or insulin resistance can mean they do not have enough to remove glucose from the blood.

The dawn phenomenon affects around half of people with type 1 or type 2 diabetes.

Other factors that could increase blood sugar at night include:

  • the time of day, as blood sugar can be more difficult to manage later in the day
  • eating late at night
  • insomnia or sleep disturbances
  • dehydration

Another proposed theory about difficulty managing blood sugar overnight is the Somogyi effect. This theory suggests that having low blood sugar in the evening could result in “rebound” high blood sugar to compensate.

However, researchers do not believe there is enough evidence to support the existence of the Somogyi effect. People who have high blood sugar in the morning also tend to have high blood sugar during the evening or night, too.

People who notice they have consistently high blood sugar at night should discuss this with a diabetes health professional. It may be necessary to adjust the timing or dosage of their insulin or to use a different method of administering it.