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Dawn Phenomenon: What It Is, Causes & How to Fix It

November 27, 2017
February 28, 2022

Are you noticing that your blood glucose is highest in the morning when you wake up and you haven’t even had anything to eat yet? Don’t worry! This is a very common effect known as the dawn phenomenon. Let’s take a look at the science behind this phenomenon and explore strategies to help you reduce your fasting glucose.

What causes the dawn phenomenon?

The dawn phenomenon, sometimes referred to as the “dawn effect,” has earned its name from the recurrence of elevated blood glucose (a.k.a. sugar) around the hours of waking, roughly between 4-8 AM. Although the exact underlying causes of the dawn phenomenon are still unclear, it is known that hormones, including adrenaline, cortisol, glucagon, and growth hormone, play a large part. These hormones follow a circadian rhythm, or a daily cycle, and tend to be found in higher concentrations in the blood in the morning to help prepare us for the day ahead.

The hormones that promote glucose release into the blood include:

  • Adrenaline: Known as the “fight or flight” hormone, adrenaline increases blood flow to the muscles and promotes the release of glucose into the blood.
  • Cortisol: Known as the “stress hormone”, cortisol also plays a role in increasing blood glucose.
  • Glucagon: Signals the liver to release glucose into the blood.
  • Growth Hormone: Important for repair and regeneration and promotes the release of glucose into the blood.

Two key processes occur in the liver overnight that result in the release of glucose into the bloodstream and contribute to increased morning blood glucose:

1) Glycogenolysis, the breakdown and release of stored glucose (a.k.a. glycogen)

2) Gluconeogenesis, the creation of glucose from components of protein (i.e. certain amino acids) or fat (i.e. glycerol)

One more hormone that plays an important role is insulin. When blood glucose rises, insulin is released and helps move glucose out of the blood and into cells for energy use or storage.

Does the dawn phenomenon occur only in people with prediabetes and type 2 diabetes?

The physiological processes that underlie the dawn phenomenon occur in everyone regardless of whether they have diabetes or not. The difference lies with insulin and how our bodies react to it. Healthy individuals secrete enough insulin and are insulin sensitive enough to counteract a rise in morning blood glucose. However, someone with prediabetes or type 2 diabetes is insulin resistant and/or may not secrete enough insulin, which allows blood glucose to rise. This may be further compounded in the early morning hours because our body is more insulin resistant compared to the rest of the day (1) causing an elevated fasting glucose to remain elevated longer. Progression of prediabetes and type 2 diabetes is likely to result in a worsening of the dawn phenomenon as insulin function and sensitivity continue to diminish.

Is the dawn phenomenon something I need to fix?

The dawn phenomenon is not necessarily something that needs to be fixed. It’s important to keep in mind that even though your fasting glucose may be elevated, you may have lower or normal glucose values throughout the rest of the day. Additionally, it’s not uncommon for patients reversing their diabetes through nutritional ketosis to experience the dawn phenomenon and still see improvements in their HbA1c. Why? Because HbA1c is a measure of your blood glucose over the last 3 months. The average value matters more than any individual blood glucose value.

Example blood glucose curve of someone controlling their type 2 diabetes through nutritional ketosis who experiences the dawn phenomenon (2)

Dawn phenomenon blood sugar graph

How can I combat the dawn phenomenon? Will reducing my carb intake help?

If you want to understand if elevated morning blood glucose numbers are a result of the dawn phenomenon or from too many dietary carbohydrates, all you need to do is test at multiple times throughout the day. First and foremost, you should be familiar with what your fasting glucose looks like. Whether it be your most recent lab values from the doctor or checking your glucose with a meter, the best way to know where your fasting glucose falls is to measure it, and to test it on a few different days. Similarly, testing your glucose throughout the day, before and after meals, and before you go to bed can help you understand how your body responds to the food you eat.Once you’ve tested enough that you understand your baseline glucose with your current habits, try incorporating each of the strategies outlined below into your routine. Continue testing your blood glucose and you’ll see what impact each change has on your morning fasting glucose.

Strategies that may help mitigate the Dawn Phenomenon:

  • Get a good night of sleep—6 to 8 hours each night—and go to bed before midnight to help reduce cortisol and improve one’s ability to tolerate glucose. (3)
  • Reduce your overall carbohydrate intake* (always with medical supervision) to lower blood glucose.
  • Eat dinner earlier in the evening and avoid late night snacks to reduce blood glucose in the evening.
  • Have your last meal of the day contain the least amount of carbohydrates to minimize the rise in blood glucose.
  • Do something active after dinner, such as a walk, to help lower blood glucose.
  • Eat a breakfast a lower in carbohydrates since blood glucose is high and you have greater insulin resistance in the morning.
  • Don’t wait too long to eat breakfast when you wake up. Eating food early in the morning can help release insulin which can lower blood glucose

A note about safety

*I do not recommend that people with diabetes or prediabetes make large-scale dietary changes without medical supervision, especially if taking medications for diabetes or blood pressure. Reducing carbohydrate consumption can decrease blood glucose and blood pressure, and a physician can help safely adjust medications so that blood glucose or blood pressure don’t get too low. Hypoglycemic (low blood sugar) and hypotensive (low blood pressure) episodes can be very dangerous.

To learn more about how food affects blood sugar, check out Dr. Sarah Hallberg's video series here:

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  1. Porcellati F, Lucidi P, Bolli GB, Fanelli CG. Thirty Years of Research on the Dawn Phenomenon: Lessons to Optimize Blood Glucose Control in Diabetes. Diabetes Care. 2013;36(12):3860-3862. doi:10.2337/dc13-2088.
  2. Monnier L, Colette C, Dejager S, Owens D. Magnitude of the Dawn Phenomenon and Its Impact on the Overall Glucose Exposure in Type 2 Diabetes: Is this of concern? Diabetes Care. 2013;36(12):4057-62: doi: 10.2337/dc12-2127
  3. Spiegel K, Leprouit R, Van Cauter E. Impact of Sleep Debt on Metabolic and Endocrine Function. Lancet. 1999;354(9188):1435-9: doi: 10.1016/S0140-6736(99)01376-8