Sunday, September 24, 2023

Early Morning Hyperglycaemia: Dawn Phenomenon or Somogyi Effect?

In diabetes, the aim of medicines and insulin is to prevent blood glucose from rising too much. However, in some situations, blood glucose increase happens not due to eating carbohydrates or taking incorrect medicines.

In this article, I will cover two interesting ways blood glucose can increase in the early mornings, a time when you are typically sleeping.

Exhibit 1. Summary of Early Morning Hyperglycaemia Causes. Image Credit: Quang Nguyen Vinh on Pexels


When your fasting blood glucose is above 125 mg/dL or two-hour post-meal blood glucose is above 153 mg/dL, experts call it high blood glucose or hyperglycaemia. Some others consider 180 mg/dL or 200 mg/dL as the cutoffs instead of 153 mg/dL. The exact number does not matter for understanding this article.

If you eat a big, high-carbohydrate meal, your blood glucose can shoot up, which can trigger your pancreas to release insulin, which then helps lower blood glucose.

In people with diabetes, insulin is either insufficient or ineffective (or both) and the blood glucose does not come down. They have to take medicines or insulin injections to lower it.

Causes of Hyperglycaemia

Hyperglycaemia can happen in:

  • Normal people due to excessive carbohydrate intake; and
  • Diabetic people due to a similar big meal or improper medicine intake.

A few other causes of high blood glucose are stress, dehydration, and infections such as colds and flu.

All of these can be monitored and controlled. However, there is a special type of hyperglycaemia which happens early morning while you are sleeping and so offers very little control.

Dawn Phenomenon

As the morning approaches, your body gets primed for the awakened state. After 3 a.m., it starts releasing hormones such as cortisol, adrenaline, glucagon, and growth hormone, which instruct your liver to increase glucose production for your body’s energy needs. So you may be fast asleep, but your blood glucose rises at the break of dawn. This is called the Dawn phenomenon.

In a normal person, increased glucose instructs the pancreas to release insulin, which brings the blood glucose level down. However, a diabetic person’s body is not able to decrease his blood glucose by itself. Since the person is sleeping, he cannot take medicines or insulin injections. So in some diabetic patients, blood glucose can reach hyperglycaemic levels.

Dawn phenomenon affects both type 1 and type 2 diabetics.

Somogyi Effect

There is another way early morning blood glucose can shoot up.

If a diabetic person has an episode of low blood glucose or hypoglycaemia overnight, the body responds to that stress with a hormone surge bigger than normal. This causes blood glucose to bounce back strongly from its lows and is called Rebound hyperglycaemia.

It is also known as the Somogyi effect, named after Dr. Michael Somogyi who first wrote about it in the 1930s.

Modern research has disputed the existence of the Somogyi effect but there is evidence on both sides of the argument: some trials have found the Somogyi effect and some recent ones have not.

Type 1 diabetics are more likely to be affected than type 2 diabetics.

The Difference Between Dawn Phenomenon and Somogyi Effect

The Dawn phenomenon occurs naturally while the Somogyi effect is due to low blood glucose overnight.

The Somogyi effect is less common than the Dawn phenomenon.

If you wake up and test your blood glucose at 3 a.m., you can find out which of the two is causing your hyperglycaemia:

  • Lower than normal blood glucose levels suggest the Somogyi effect; and
  • Normal or high blood glucose levels indicate the Dawn phenomenon.

How To Prevent Dawn Phenomenon

Since the Dawn phenomenon is natural, you cannot do much to prevent it. Neither do diabetes medicines help nor does long-acting insulin because you will need to take them before going to sleep, which can cause low blood glucose in the early part of the night.

One option is waking up at 4 a.m. and taking your diabetes medicines in anticipation. But that is not practical.

However, you can avoid eating carbohydrates before bedtime to reduce the severity of the Dawn phenomenon.

A modern option is the use of a Continuous Glucose Monitor (CGM) with an insulin pump. The former measures your blood glucose even when you are sleeping and based on its readings, the pump adjusts insulin injected into your body—the two do what you would have done if you were awake during the episode.

How To Prevent Somogyi Effect

Since the Somogyi effect is a result of low blood glucose overnight, preventive measures include:

  • Avoiding late evening exercise; and
  • Testing for blood glucose before sleeping and adjusting for your medicines and insulin to prevent low blood glucose.

The best option, once again, is the combination of a Continuous Glucose Monitor and an insulin pump.


  • Everyone gets high blood glucose in the early morning.
  • In diabetics, it can lead to hyperglycaemia.
  • The Somogyi effect can cause hyperglycaemia if a diabetic person has an episode of low blood glucose overnight.
  • Both these types of hyperglycaemia are controlled by a good CGM with an insulin pump.
  • Talk to your doctor about early morning hyperglycaemia, if your morning blood glucose is regularly high while it is in control for the rest of the day. Do not do any changes to your medicines or insulin injections on your own.

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First Published on: 9th August 2023
Image Credit: Johannes Plenio on Pexels


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