What causes high morning blood sugar, and how can you lower it?

If you have high blood sugar first thing in the morning, before you’ve eaten, there are a few possible reasons.

It could be due to hormones telling your liver to wake you up by releasing blood sugar (glucose). 

It could also be a sign that your body is becoming resistant to a hormone called insulin, which tells your cells to absorb sugar from your blood.

Making changes to when and what you eat before you go to bed could be one way to manage high morning glucose levels. Exercise can also help.

ZOE runs the world’s largest scientific study of nutrition and blood sugar responses in the world, with over 15,000 participants so far. Our research shows that everyone responds differently to food.

Managing morning blood sugar involves some trial and error, which is why it helps to have a clear picture of your body’s blood sugar and responses to different foods. 

Our at-home test analyzes your blood sugar and blood fat levels before and after eating — as well as your unique community of gut bacteria — to help you understand which foods are best for you.

You can find out more by taking our free quiz.

Read on to learn more about why you may have high morning blood sugar.

Why your blood sugar is high in the morning

According to the American Diabetes Association, there are three main causes of high blood sugar in the morning:

  • the dawn phenomenon

  • low overnight insulin levels

  • the Somogyi effect

The dawn phenomenon

Everyone has fluctuations in the hormones that control blood sugar levels, including cortisol and insulin, and your blood sugar levels vary throughout the day. 

In a complex cascade of interactions between different parts of the body, a surge of the hormone cortisol in the morning hours tells your liver to release glucose into the bloodstream. 

This high blood sugar — known as hyperglycemia — triggers your body to release more insulin, which will usually keep blood glucose levels in the bloodstream within a normal range in individuals without diabetes.

In people with prediabetes or diabetes, morning blood sugar can remain high as the body becomes less sensitive to insulin or produces smaller amounts of insulin.

This is known as the “dawn phenomenon.”

High blood sugar in the mornings affects roughly half of all people with type 1 and type 2 diabetes.

Low insulin levels during the night

You may experience low insulin levels during the night if you take supplemental insulin, either from a pump or daily injections. Most often, there are three reasons that insulin levels might be too low overnight, leading to raised morning blood sugar:

  • Your insulin pump is not set to give you a high enough dose of background insulin (or basal insulin) overnight.

  • Your injection of long-lasting insulin doesn’t provide a high enough dose. 

  • You injected the long-lasting insulin too early in the day, and its effects have reduced overnight.

The Somogyi effect

The Somogyi effect is named after chemist Michael Somogyi, who first described it in the 1930s.

If you are taking supplemental insulin but skip dinner without adjusting your insulin, your blood sugar can dip too low while you sleep. 

Occasionally, your liver makes up for this by releasing more glucose, meaning that you wake up with raised blood sugar. 

This can also happen when a person living with diabetes takes too large a dose of insulin after dinner. Taking too much insulin suppresses blood sugar levels too far while you’re asleep, triggering the liver to release glucose.

What are normal and high morning blood sugar levels?

The term “morning blood sugar” describes your blood sugar level after you wake up but before you eat anything. This “fasting” measurement shows how well your body controlled your blood sugar overnight.

When you eat, it leads to a rise in blood sugar. Insulin lets the sugar leave your blood and enter the cells in your body, converting it into useful energy.

If you don’t regularly monitor your blood sugar to manage a condition like diabetes, you may not be aware of your fasting blood sugar level. But you might want to understand what your levels mean if you get a result back from your regular physician’s checkup.

Consistently high blood sugar can cause tiredness and mental fogginess and can lead to serious health problems if untreated, but most mild cases cause no noticeable symptoms at all. 

Most people learn they have high blood sugar after seeing a doctor about something else.

What units are used for measuring blood sugar levels?

Doctors measure blood sugar differently depending on where you live:

  • In the U.S., your blood sugar reading mostly shows as milligrams of glucose in 1/10th of a liter of blood, also known as milligrams per deciliter (mg/dL).

  • In the U.K., doctors often measure your blood sugar levels in millimoles of glucose per liter of blood (mmol/L). 

Whichever measurement a test uses, it’s to compare your level to a normal blood sugar range. 

If you live with diabetes, you’ll have higher blood sugar levels than someone who doesn’t have diabetes. So, a “normal” blood glucose level for a person with prediabetes or diabetes is higher.

There are other ways to measure blood sugar, such as a hemoglobin A1C (HbA1C) test that estimates the average blood sugar levels over the last 3 months. 

What should my blood sugar levels be when I wake up?

Your blood sugar levels should be below 100 mg/dL (5.6 mmol/L) if you don’t have diabetes.

Recent ZOE research found that the average fasting glucose of participants without diabetes was 91 mg/dL (5.05 mmol/L). 

If your fasting glucose before breakfast is 100–125 mg/dL (5.6–6.9 mmol/L), it’s higher than doctors would expect in a person with healthy blood sugar control. 

Fasting blood glucose in this range means you could have prediabetes — a health condition that significantly increases your risk of developing type 2 diabetes, heart disease, and stroke. 

What fasting blood sugar level means you have diabetes?

A doctor will make a diagnosis of diabetes when someone has a fasting blood sugar level that’s 126 mg/dL (7 mmol/L) or higher on at least two different occasions

It’s a sign that your body either isn’t sensitive enough to insulin or doesn’t produce enough insulin to control blood glucose appropriately.

How blood sugar testing could help you

Whenever you eat, your blood sugar level rises, before dropping again some time later. This is called a postprandial, or post-meal, response and is perfectly normal. 

However, some foods cause your blood sugar to rise much higher than others, such as simple carbohydrates. These “spikes” can lead to bigger dips afterward due to large amounts of insulin released in response to the sugar spike. This can leave you feeling tired or lacking in energy.

Over time, this pattern can increase your risk of metabolic diseases like heart disease and type 2 diabetes. 

Importantly, ZOE’s research has shown that everyone responds differently to foods. This means a food that’s fine for one person’s blood sugar may cause others to spike, and vice versa.

ZOE’s at-home test uses a sensor called a continuous glucose monitor (CGM) to measure your blood sugar levels throughout the day and night, before and after you eat. This helps us to see how different foods affect your levels.

But unlike having just a CGM, our tests also look at your blood fat levels and your gut microbiome — the bacteria and other microorganisms that live in your gut. These are both linked to your metabolic health, too.

The ZOE program analyzes all of this information to give you personalized recommendations that can help you eat the best foods for your unique metabolism and avoid the responses associated with worse metabolic health.  

You can take a free quiz to find out more.

How to lower high morning blood sugar

Diet changes, weight management, and regular exercise are helpful for managing morning blood sugar levels. 

1. Build a clear picture of how your blood sugar works by using a CGM

As we’ve seen, everyone’s blood sugar control works differently, so it can be helpful to know whether morning spikes are a problem for you. 

Unless you have diabetes, it is unlikely that you check your glucose regularly. 

Checking your glucose a few times throughout the day or continuously via CGM can help to show how your body is handling changes in glucose levels during fasting or after meals. 

2. Spot the pattern

Look at the information coming from your blood sugar sensor and when your spikes happen. If it shows that you consistently wake up with mildly high blood sugar or experience it overnight, what or when you eat may have a role to play.

For people with diabetes, it could also mean that you’re not using enough insulin or are injecting at the wrong time of day. 

But for people without the condition, it mainly points to the need for making important but simple diet and meal schedule changes.

3. Avoid late-night meals and snacks

If you’re producing enough insulin and your cells are responding to it, the dawn phenomenon isn’t a likely culprit for your high morning blood sugar levels. 

In a recent study, researchers found that eating dinner at 6 p.m. improved 24-hour blood glucose results, while eating at 9 p.m. made them worse. 

The results don’t necessarily confirm that eating later makes your personal blood sugar high after you wake up, but they do suggest that late dining could make it harder to control your levels. 

Even one late-night meal seemed to make a difference in glucose control over a 24-hour period the next day. 

Timing is important as seen above, but the type of food is also important to keep your glucose in check. 

Knowing the relationship between different foods and how your body responds to them can be a key to balancing glucose levels. 

4. Try doing more exercise

Working out uses blood glucose for fuel, moving it from your blood to your muscles. A 2021 review found that exercise helped people living with and without diabetes control their fasting blood glucose.

If you find that you tend to wake up with high blood sugar, try going for a run, following a YouTube workout, or booking yourself into gym classes. This could help you bring down your morning blood sugar spikes.

5. Weight management

Weight loss has been shown to decrease insulin resistance. This helps improve glucose control, and it likely reduces the risk of developing diabetes in those who don’t already have the condition.

But losing weight can be challenging. Work with a healthcare professional to find out what weight range to aim for to support your individual health. 

Our unpublished research found that people who closely followed their personalized ZOE nutrition program lost 9.4 pounds on average, and over 80% said they had more energy and didn’t feel hungry.

When to speak to your doctor

If you try eating earlier, sticking to healthier meals, and exercising without seeing a drop in your fasting blood glucose, it might be time to speak to your doctor about further testing and treatment options. 

Tests like the HbA1c can help your doctor confirm whether you’d benefit from medical treatment. This test shows your average blood glucose levels over the last 3 months. 

Your doctor may recommend controlling your fasting blood sugar level through diet or exercise if it’s high enough to suggest prediabetes. 

If type 2 diabetes is developing, they may prescribe medication or insulin injections if it becomes moderate to severe, but it’s possible for many people to manage type 2 diabetes with exercise and diet alone.

If you already have a diabetes diagnosis and take insulin, speak to your healthcare provider about whether they can change your dose or type of insulin or recommend a shift in your medication schedule.


If you live with diabetes and have high blood sugar when you wake up, it’s usually for one of two main reasons: the dawn phenomenon or an insulin schedule or dosage that isn’t working for you. Your body might also be overcorrecting low blood sugar from during the night.

Doctors suggest that a normal fasting blood sugar range is between 70–100 mg/dL (3.9–5.6 mmol/L). If your fasting blood sugar is consistently over 126 mg/dL (7 mmol/L), your doctor will diagnose diabetes.

You can reduce your risk of high fasting blood sugar by eating your dinner earlier the night before. If you use insulin, it’s important to take the right dose at the right time to keep your blood sugar regular overnight.

Repeated blood sugar spikes and dips after you eat can increase your risk of type 2 diabetes and other metabolic diseases. 

ZOE’s at-home test helps you to understand your personal responses to food and choose the best foods for you. 

Take our free quiz to find out how ZOE could benefit your health.


Acute effect of late evening meal on diurnal variation of blood glucose and energy metabolism. Obesity Research & Clinical Practice. (2011). https://www.sciencedirect.com/science/article/abs/pii/S1871403X1100007X

All about your A1C. (n.d.). https://www.cdc.gov/diabetes/managing/managing-blood-sugar/a1c.html

Antidiabetic effects of physical activity: how it helps to control type 2 diabetes. Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy. (2020). https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC7443456/ 

Blood glucose monitoring. StatPearls. (2021). https://www.ncbi.nlm.nih.gov/books/NBK555976/ 

Diagnosis. (n.d.). https://www.diabetes.org/diabetes/a1c/diagnosis

Eating dinner early improves 24-h blood glucose levels and boosts lipid metabolism after breakfast the next day: a randomized cross-over trial. Nutrients. (2021). https://pubmed.ncbi.nlm.nih.gov/34371933/ 

Enhanced insulin sensitivity in successful, long-term weight loss maintainers compared with matched controls with no weight loss history. Nutrition & Diabetes. (2017). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5519190/

High morning blood sugars. (n.d.). https://www.diabetes.org/diabetes/treatment-care/high-morning-blood-glucose 

Hyperglycemia. StatPearls. (2021). https://www.ncbi.nlm.nih.gov/books/NBK430900/ 

Insulin resistance & prediabetes. (2018). https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance

Measures of optimal glucose “time in range” and variability using continuous glucose monitors in 4,805 healthy non-diabetic individuals is discriminatory of cardiovascular health risk. Proceedings of the Nutrition Society. (2022). https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/measures-of-optimal-glucose-time-in-range-and-variability-using-continuous-glucose-monitors-in-4805-healthy-nondiabetic-individuals-is-discriminatory-of-cardiovascular-health-risk/C5E2BB7C6B3CFCCDC428801C97EE3C33 

Millimoles per liter. (2021). https://awog.org/womens-health/health-library?DOCHWID=stm159571 

Prediabetes — your chance to prevent type 2 diabetes. (2021). https://www.cdc.gov/diabetes/basics/prediabetes.html

The Dawn Phenomenon revisited: Implications for diabetes therapy. Endocrine Practice. (2005). https://www.sciencedirect.com/science/article/abs/pii/S1530891X20399572