The Dawn Phenomenon: Why Morning Blood Sugar Is High
Have you ever gone to bed with blood glucose in your target range, eaten nothing overnight, and still woken up with a high reading? You are not alone. Early-morning high blood glucose is common in people with diabetes. One frequent cause is the dawn phenomenon, a natural rise in blood glucose in the early morning hours. This guide explains what the dawn phenomenon is, how it differs from other causes of morning highs, how to figure out what is happening, and ways to manage it with your care team.
What is the dawn phenomenon?
In the early morning, typically between about 3 a.m. and 8 a.m., the body releases hormones such as cortisol, growth hormone, glucagon, and adrenaline (epinephrine). These hormones help prepare the body to wake up and be active. They signal the liver to release glucose and make the body temporarily less sensitive to insulin.
In people without diabetes, the pancreas releases extra insulin to balance this rise. In people with diabetes, the body may not make enough insulin or may not respond to it well enough, so blood glucose rises. The result is a higher-than-expected fasting or wake-up glucose reading.
The dawn phenomenon can happen in people with type 1 or type 2 diabetes. It varies from person to person and from day to day.
Other causes of high morning blood glucose
Not every morning high is the dawn phenomenon. Other possible causes include:
Waning insulin or medicine
If your long-acting insulin or other medicine wears off before morning, or the dose is too low, glucose can rise overnight. The timing of evening doses matters.
Evening eating
A large dinner, a late-night snack, or a high-fat meal (which can slow digestion and cause a delayed rise) can keep glucose elevated overnight. See the glycemic index explained.
Rebound after an overnight low (Somogyi effect)
In the past, morning highs were often attributed to the "Somogyi effect," in which an overnight low triggers the release of stress hormones, causing a rebound high by morning. Research using continuous glucose monitoring suggests this is less common than once thought, and the dawn phenomenon or insufficient insulin are more frequent explanations. Still, overnight lows do happen and can be dangerous, so it's important to find out whether you are having them. See hypoglycemia.
Other factors
Illness, stress, poor sleep, missed medicine doses, insulin pump problems, and some medicines such as corticosteroids can also raise morning glucose. See stress and blood sugar and sleep and diabetes.
How to tell what's causing your morning highs
To figure out the cause, you need information about what your glucose does overnight.
Use a continuous glucose monitor
A CGM shows your glucose pattern through the night. With the dawn phenomenon, glucose is usually stable during the night and then rises in the early morning hours. With waning insulin or a late meal, glucose may rise steadily through the night. With an overnight low, you will see a drop before a rise. See checking blood sugar and CGMs.
Check overnight with a meter
If you don't use a CGM, your care team may suggest checking your glucose at bedtime, around 2 or 3 a.m., and when you wake up, for several nights. Patterns are what matter, not a single night.
- Normal at bedtime, normal at 3 a.m., high on waking: suggests the dawn phenomenon.
- Low at 3 a.m., high on waking: suggests an overnight low followed by a rebound; this needs prompt attention from your care team.
- Already high at bedtime or rising throughout the night: suggests evening food, too little medicine, or the medicine wearing off.
Keep notes
Write down what and when you ate in the evening, your medicine doses and timing, activity, alcohol, stress, and sleep. Share your records with your care team.
Managing the dawn phenomenon
Never change your medicine doses or timing on your own. Talk with your care team about options such as:
Adjusting medicines
- Changing the timing of long-acting insulin or other medicines.
- Adjusting the dose of evening or bedtime insulin.
- Switching to a different type of long-acting insulin that provides steadier coverage.
- Insulin pumps can be programmed to deliver more basal insulin in the early morning hours. Automated insulin delivery systems can adjust insulin automatically in response to rising glucose. See insulin basics.
- Other diabetes medicines may be adjusted or added for people with type 2 diabetes. See metformin and common diabetes medications.
Adjusting evening eating
- Eat dinner earlier in the evening if possible.
- Consider a smaller, lower-carbohydrate dinner or bedtime snack, or choose a snack with protein and fat instead of mostly carbohydrate.
- Be mindful of high-fat meals, which can cause delayed rises.
- If your care team has advised a bedtime snack to prevent lows, don't skip it without discussing it first.
Physical activity
Some people find that activity in the evening, such as a walk after dinner, helps lower overnight and morning glucose. Morning activity can also help bring glucose down after waking. See exercise and diabetes.
Breakfast
Eating breakfast can help some people because it stops the liver from continuing to release extra glucose. Others find their glucose rises more after breakfast than after other meals because of morning insulin resistance, and choose a lower-carbohydrate breakfast. Check your glucose after breakfast to learn your response.
Healthy habits
Consistent sleep, stress management, and regular activity support more stable glucose overall.
Is the dawn phenomenon dangerous?
An occasional higher morning reading is not an emergency. But persistently high fasting glucose contributes to a higher A1C and the long-term risks that come with it. Addressing morning highs can be an important part of reaching your goals. See A1C and blood sugar targets and how to lower A1C.
For many nonpregnant adults with diabetes, the American Diabetes Association suggests a fasting and pre-meal glucose target of 80 to 130 mg/dL, but your targets may be different. NIDDK explains how to know your blood sugar numbers, and MedlinePlus offers tips on managing your blood sugar.
When to call your care team
Contact your care team if your morning glucose is consistently above your target, if you find lows overnight, if you wake with symptoms such as sweating, headache, or nightmares, or if morning highs come with ketones or feeling unwell.
Frequently asked questions
Does everyone with diabetes have the dawn phenomenon?
No. Many people with diabetes experience some early-morning rise, but the size of the rise varies widely. Some people notice it only occasionally, while others see it most mornings.
Can the dawn phenomenon happen in people without diabetes?
The early-morning release of hormones happens in everyone. People without diabetes simply make enough extra insulin to keep glucose in a normal range, so they rarely notice it.
Will skipping breakfast lower my morning glucose?
Not necessarily. For some people, glucose keeps rising until they eat, because the liver continues releasing glucose. For others, breakfast causes a larger rise. Check your glucose and talk with your care team about what works for you.
Is a high morning reading a reason to take extra insulin?
Only if your care team has given you a correction plan. Taking extra insulin without guidance can lead to lows later in the morning, especially if you exercise or eat less than usual.
Key takeaways
- The dawn phenomenon is an early-morning rise in blood glucose caused by natural hormone release.
- Other causes of morning highs include waning medicine, evening eating, illness, and, less commonly, rebound from an overnight low.
- CGM data or overnight checks help identify the cause.
- Treatment options include adjusting medicine timing or doses, pump settings, evening meals, and activity; work with your care team.
Sources
Links to the sources cited above appear in the text. We rely on the Centers for Disease Control and Prevention (CDC), the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), and the American Diabetes Association (ADA).
Related guides: Blood sugar and treatment
- A1C and Blood Sugar Targets: Understanding Your Numbers
- Checking Blood Sugar: Meters and Continuous Glucose Monitors
- Hypoglycemia (Low Blood Sugar): Signs, Treatment, and Prevention
- High Blood Sugar and Diabetic Ketoacidosis (DKA)
- Insulin Basics: Types, Delivery, and Safety
- Metformin and Common Diabetes Medications
- Managing Diabetes When You're Sick
- How to Lower Your A1C: Proven Strategies