People usually have slightly higher blood sugar levels in the morning. However, in some people with diabetes, these levels can be significantly higher.

Diabetes is a condition that impairs the body’s ability to process blood glucose. Without careful management, blood sugar levels can become too high, which is known as hyperglycemia. Long periods of high blood sugar levels can result in health complications.

Even when a person carefully controls the condition, they may notice blood sugar spikes in the morning. There are three main causes of high blood sugar in the morning:

It is important to note that this article refers to effects experienced in the morning, but these effects may occur anytime a person sleeps for a long period. People who work at night and sleep during the day can also experience these effects.

In this article, we will explore these causes, including what they can mean for a person’s health and when to see a doctor.

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The dawn phenomenon refers to periods of hyperglycemia that occur during the early morning hours. The shift in blood sugar levels happens as a result of hormonal changes in the body.

Hormones, such as cortisol, glucagon, epinephrine, and growth hormone are known as counter-regulatory hormones. They can cause blood sugar levels to rise. The activity of cortisol and growth hormone normally increases each day to stimulate the liver to produce glucose at dawn.

This is why everyone experiences a slight rise in their blood glucose levels to some extent in the morning. A person without diabetes will not experience adverse effects, as their body can produce insulin to adjust. However, a person with diabetes is unable to produce sufficient or effective insulin. As such, this can cause a spike in their blood sugar levels and may require treatment to adjust their levels.

When the dawn phenomenon occurs, it may coincide with when nighttime levels of insulin begin to taper off. Reasons for the drop in insulin can vary. However, it often occurs when a person administers too little basal insulin, or when they inject it too early, causing its effects to wear off earlier than desired.

Different types of insulin work at different speeds and durations. Most types reach a peak when they are most effective. After the peak, the insulin’s effect begins to wear off. If people notice their blood glucose increasing overnight, then they may need to adjust their basal insulin and increase the dosage.

Some scientists believe there is another cause of high blood sugar in the morning: the Somogyi effect, also called rebound hyperglycemia. Named after Dr. Michael Somogyi, this theory suggests that blood sugar levels rise in response to a bout of late night hypoglycemia, or low blood sugar. This could occur if a person administers too much insulin or does not eat enough food before bed.

Not all experts agree on the Somogyi effect, and the scientific community still debates the theory. However, a 2015 study shows that the Somogyi effect was the most common cause of fasting hyperglycemia in individuals with type 1 diabetes and poor glycemic control.

If a person begins to notice a frequent occurrence of morning hyperglycemia, then they should check their blood sugar levels at bedtime, in the middle of the night, and upon waking to better understand their glucose patterns and identify the cause.

A person can use a continuous glucose monitor (CGM) to help them track and monitor their blood glucose throughout the night and day. This wearable medical device can collect data on a person’s blood sugar levels while they sleep.

Treatment options will vary depending on the data the CGM or individual glucose checks provide. By tracking when the highs and lows occur, a doctor will be able to recommend suitable strategies.

If the data shows that a person has high blood sugar at bedtime, then it is likely that food and medication are responsible. If a person has hyperglycemia before they sleep, it can persist until morning. Either a large meal close to bedtime or using too little insulin may be the cause. A person can adjust this by changing what and when they eat and slightly increasing their insulin dosage.

If a person is within their target range at bedtime but wakes with high blood sugar, they may be using too little basal medication or using it too early. Changing the timing of the long-acting dose, switching to a twice-daily basal insulin, or using an ultra-long-acting basal insulin may be beneficial.

Data demonstrating that a person has high blood sugar between roughly 3–8 a.m. suggests the dawn phenomenon. In this case, a doctor may recommend that a person does not increase their long-acting insulin, as this could cause hypoglycemia during the night. It may be advisable to consider an insulin pump, as a person can program it to automatically deliver more insulin in the early morning hours.

Some research also indicates that the following lifestyle changes may help control morning glucose levels.

  • exercising in the evening
  • increasing the proportion of protein to carbohydrates in the evening meal
  • eating breakfast every day

Anyone who experiences high blood sugar levels in the morning should speak with a healthcare provider, who will identify an effective way to manage these levels.

If a person does not receive appropriate treatment, regularly experiencing high morning glucose levels can increase their risk of:

It is important for a person with diabetes to be aware that their blood sugar levels may rise in the morning and to receive treatment if this occurs.

If high glucose levels persist and get worse, complications can arise. For example, in people with type 2 diabetes, insulin resistance will increase, and the condition can progress more rapidly, which can increase the risk of potential health complications.