Information for those Newly Diagnosed with Diabetes
Hyperglycemia from the
Dawn & Simogyi Effects

What is the Dawn Effect?
(also called Dawn Phenomenon)

The dawn effect is an increase in insulin resistance (decrease in insulin sensitivity) caused by hormones released about two hours before you wake. These hormones are under the control of the pituitary gland in the brain. The dawn effect is also influenced by testosterone and tends to be more significant in men and women with polycystic ovarian syndrome who may have elevated testosterone levels.

This resistance to insulin can cause you to need more at certain times during the night.  The Dawn Effect occurs in nondiabetics as a means to elevated blood glucose to prepare for the day.  In persons without diabetes, the body adjusts so that blood glucose levels do not go too high.  In persons with diabetes, however, the Dawn Effect can cause blood glucose levels to rise too high and lead to morning fasting hypoglycemia.

Your overnight insulin is taken to counter the Dawn Effect, and on average, diabetics take 20% of their total daily insulin overnight due to an increase in metabolic needs during the night.  People using on insulin pumps often have increased basal rates after 3 a.m. for this reason.

It is a normal occurrence in all people to experience a slight rise in blood glucose levels before rising, but this phenomenon is more pronounced in persons who need to take insulin.  The Dawn Effect is also the most common cause of nighttime highs.

What is the Simogyi Effect?
(also called Rebound Hyperglycemia)

The Simogyi Effect occurs after a rapid drop in blood glucose levels sometime during sleep.  The body responds by releasing stored glucose (released from glycogen stores) from the muscles and liver in an attempt to elevate blood glucose levels. The body may overcompensate, releasing large amounts of glycogen which results in a "rebound" effect, causing hyperglycemia termed "Simogyi Effect."

This may happen anytime during sleep, but hypoglycemia usually occurs around 3 a.m.  The hypoglycemic (low blood glucose) episode is followed by an elevated is followed by an elevated blood glucose level towards morning.  Going to bed without a snack or low blood-glucose, inadequate food eaten for exercise, and too much insulin contribute to this response.


The Dawn Effect is the early-morning increase in blood glucose, usually between 4 a.m. and 8 a.m. in persons with diabetes.  The exact cause isn't known, however, it can be responsible for persistently elevated fasting blood glucose and HbA1c levels.  It is not caused by a previous low during the night and treatment involves limiting fat in the diet at dinnertime and in bedtime snacks.  Changes in insulin doses during the night are often required and should be made by your doctor.

The Simogyi Effect is triggered by low blood glucose that causes a release of hormones including glucagon that raise blood glucose too much.  Low blood glucose occurs most often near an insulin peak so you may need to test your blood glucose levels more often for a few days to see where your lows are beginning.

To prevent or correct high blood glucose levels in the morning, your doctor may recommend:

  • Adjusting your dosage of medication or insulin
  • Switching to a different medication
  • Changing the time or fat content of your dinner and bedtime snack
  • Testing your blood glucose around 3.a.m.