The Dawn Phenomenon


This content was made possible with support from Medtronic Diabetes, an active partner of Beyond Type 1 at the time of publication.

Editor’s Note: This content was verified by Nalani Haviland MCMSc, PA-C, lead clinician, Pediatric Diabetes. 

“A high morning reading ruins my whole day!”

As a physician assistant specializing in diabetes, I hear this quite often. It’s my job to help, but it can be a tough one to figure out. Frequently, early morning highs are caused by reactive (post-meal) hyperglycemia, overnight snacking (without covering), or a weak overnight basal. But sometimes these high patterns are caused by a more mysterious physiologic mechanism called “dawn phenomenon.” We’re going to discuss that more here, but first, let’s talk “normal” physiology and how some commonly used formulations of insulin work.

What is the dawn phenomenon?

People without diabetes have very stable levels of circulating plasma insulin and subsequent blood glucose levels overnight. Between 2-8 a.m., these plasma insulin levels increase in response to an increase in circulating growth hormone which causes a release of glucose and increased insulin resistance. This automatic increase in insulin secretion isn’t possible in people with diabetes, and can result in a noticeable rise in blood glucose levels during this overnight time period.

Dawn phenomenon is most common in teens and early adults. Work with your clinician to understand and evaluate. An evaluation for dawn phenomenon is best done using a continuous glucose monitor (CGM) over multiple nights. A rise of approximately >20mg/dL from the lowest CGM reading to the time of waking is indicative of dawn phenomenon.

Ultimately, dawn phenomenon is tricky. It is inconsistent and often misdiagnosed. There are many other reasons it can occur. For instance, an inappropriately low basal dose would lead to a noticeable rise overnight. This is likely happening during the day too, but is less noticeable because of mealtime insulin use and increased activity.

A high fat, high carb dinner may also be the cause of that those pesky morning highs. Fat delays gastric emptying resulting in the delayed digestion of carbohydrates and a later post-prandial rise. Think pizza…

It is important to rule out the Somogyi effect when evaluating for the cause of morning hyperglycemia. This phenomenon is described as hyperglycemia caused by the body’s hormonal response to a significant overnight low.

Tips for pump users

For pump users, the dawn phenomenon is much easier to counteract, as basal rates can be adjusted depending on time of day. The dawn phenomenon can often be counteracted with a basal increase of 20-30 percent. When on an insulin pump, basal rates can simply be increased, helping to prevent dawn phenomenon. It is recommended to change basal rates two to three hours prior to a rise in blood glucose, and approximately five hours prior to the high blood glucose (BG) event. When it comes to changes in basal insulin, the timing of the change is just as important as the amount! Always consult your diabetes care team before making any changes in your basal rates!

Tips for MDI users

If you aren’t pumping, things can get much more complicated. But there can be a solution—again, work with your clinician. There are many basal insulins available; Levemir, Lantus, Basaglar, Tresiba and Toujeo. To best understand how to fend off dawn phenomenon, we need to understand the mechanism of action of each.

Levemir, Lantus and Basaglar

Levemir, Lantus and Basaglar are made up of different components, but act very similarly.  All can be taken between one to two times a day. Levemir begins working within one to three hours, peaks between 8-10 hours, and has a duration of 18-26 hours. Lantus and Basaglar begin working in one to two hours, peak at six hours (less peak than Levemir) and have a duration of 18-24 hours.

These three insulins, when given at the correct time, can counteract dawn phenomenon with their peaks; Levemir given at 6 p.m. can help prevent dawn phenomenon at 2 a.m., for example. This can be difficult to time, however. For instance, a peak of long-acting insulin at 12 a.m. may be the cause of nighttime lows. Also, dawn phenomenon can happen in different times of the night in different people, or in the same person, it doesn’t happen to everyone, and it is not always consistent.

Lantus, Basaglar and Levemir can be split into two doses if they are not lasting a full 24 hours. Lantus given at bedtime may lose its efficacy around dinner the next day.  The prandial (mealtime) insulin given for dinner will work for four to five hours after that, but since Lantus takes one to two hours to kick in, there would be a gap in coverage leading to elevated morning blood glucose levels. This is often misinterpreted as dawn phenomenon and people who experience this should try splitting their doses. Analysis by using a CGM over several nights and looking at the results with your clinician can lead to better understanding.

Toujeo and Tresiba

The newest basal insulins available include Toujeo and Tresiba, both of which require one injection/day and have no true peak. This leads to very stable blood glucose levels but cannot be timed to fight dawn phenomenon. Toujeo begins working after two hours and has a duration of 36 hours. Tresiba begins working after two hours and has a duration of > 42 hours.  These longer acting insulins provide a very flat and consistent profile, great for minimizing variability, but difficult to counteract dawn phenomenon. A comprehensive table of the timeframes mentioned above can be found here.

Because of the many variables involved, episodes of dawn phenomenon are difficult to eliminate entirely. If you are having those discouraging morning highs, it’s worth it to get together with your clinician to analyze and develop solution strategies. We all like to get our days started on the right foot and feeling good!

Nalani is a Medtronic product user.