Understanding the Somogyi effect and dawn phenomenon

Diabetes nurse educator, Christine Manga, explains the causes behind elevated fasting blood glucose readings in the morning: Somogyi effect and dawn phenomenon.

Both the Somogyi effect and dawn phenomenon will lead to elevated fasting blood glucose (glucose level after an overnight fast) readings in the morning. The target for fasting blood glucose levels is <= 7mmol/L. This said, the causes are very different.

Dawn phenomenon

The dawn phenomenon occurs in everyone. However, people without diabetes will not notice it because their body is able to counteract the effects. It is caused by natural body changes during sleep.

During the night, less insulin is produced and in the early hours of the morning, hormones, such as cortisol, growth hormone, epinephrine and glucagon, are all released. These hormones all act in the opposite way to insulin, resulting in elevated blood glucose levels.

Towards the early hours of the morning, the body releases stored glucose from the liver into the bloodstream to provide energy for the coming day. This will cause a further rise in blood glucose levels. According to the American Diabetes Association, the dawn phenomenon occurs between 5:00am – 8:00am. The dawn phenomenon is a natural phenomenon.

Somogyi effect

The Somogyi effect is usually management related and is a rebound hyperglycaemia (high blood glucose). It happens in response to a nocturnal hypoglycaemia (low blood glucose).

This hypoglycaemia can be caused by giving too much insulin at night, not having an evening snack, or from doing vigorous exercise in the evening hours. In response to the hypo, the body releases hormones to raise the blood glucose levels. These include cortisol, growth hormone, glucagon and adrenaline. When you wake, you will have elevated fasting blood glucose level.

So, which one do you have: Somogyi effect and dawn phenomenon?

Due to the causes being different, the management will also differ. To establish what is causing your elevated fasting reading, you will need to do some extra blood glucose testing.

Testing your blood glucose levels between 2:00am – 3:00am on a few consecutive nights will give you an answer. If you are experiencing hypos at this time of night, then you are experiencing the Somogyi effect.

If on the other hand, your blood glucose levels are normal at this time, then you are experiencing the dawn phenomenon.

The use of continuous glucose monitoring (CGM) would be extremely useful in detecting the cause of your elevated blood glucose readings. CGM is now becoming more affordable, but definitely is still not cheap. Speak to your doctor about wearing a sensor to assist you in making management decisions.


Dawn phenomenon

To prevent the dawn phenomenon, you could:

  • Increase the amount of vigorous physical exercise in the evening hours.
  • Wear an insulin pump to administer extra insulin in the early morning hours. This would work well.
  • Reduce the amount of carbs and evening snacks.
  • Change insulin formulations to more concentrated ones. This can lead to improved fasting blood glucose levels.
  • Administer insulin later at night. This may also be beneficial.
  • There may be a need to change some of your diabetes medications, or possibly even add more.

Somogyi effect

Here are ways to prevent the Somogyi effect from occurring:

  • Reduce the amount of insulin given in the evening.
  • Once again, changing your insulin to a stronger concentration can prevent nocturnal hypos.
  • Giving the insulin earlier may also prove helpful.
  • Getting assistance with carb counting will help you to match the amount of insulin to the amount of carbs you eat, preventing overdosing of insulin.
  • Your doctor may need to assess your medication and reduce, or discontinue some.
  • Try to reduce the amount of vigorous physical activity in the evening.
  • It may also be necessary to have an evening snack before bedtime. The down side to this is that it may cause long-term weight gain.

The most important thing is that you know which one, the dawn phenomenon or the Somogyi effect, is causing your elevated fasting readings. You can only manage what you know.

eating time budget


Christine Manga (Post Grad Dip Diabetes and Msc Diabetes) is a professional nurse and a diabetes nurse educator. She has worked with Dr Angela Murphy at CDE Centre, Sunward Park since 2012.

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