Why Is My Fasting Blood Sugar High? Fasting Hyperglycemia

You haven’t eaten anything all night because you were sleeping. You expect your blood sugar to be lower in the morning, yet you see it’s high. If you're not diagnosed with diabetes, it's unlikely that you will measure it, but you may experience symptoms such as excessive thirst, frequent urination, and weakness.

High blood sugar levels while fasting can indicate that your body can't effectively reduce blood glucose levels to the normal range. This can be a cause of undiagnosed prediabetes (insulin resistance), diabetes, or poor blood glucose management in people with diabetes. Read more to learn about the causes, symptoms, diagnosis, and treatment of fasting hyperglycemia.

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How Does Fasting Affect Blood Sugar?

Your body is designed to produce energy even when you don’t eat for a long period, which most people experience overnight. This breaks down glycogen (glucose stored in your liver and muscles). 

When blood glucose levels drop due to certain factors, such as fasting or exercise, the liver and muscles break down glycogen and release glucose into the bloodstream to bring them back to normal. 

When glycogen stores are depleted during prolonged fasting, your body then breaks down fat and, if needed, protein in the muscles. When your body starts breaking down fat, it produces molecules called ketones for energy. However, these physiological mechanisms can have different health implications for people with normal blood glucose levels and those with prediabetes or diabetes.¹ 

Healthcare providers check your blood glucose levels after at least 8 hours of fasting. They expect your blood glucose levels not to be high due to overnight fasting. However, if you have conditions related to insulin and other hormones, the physiological mechanism mentioned above may not bring everything back to the normal range. Instead, it can cause a different problem: high fasting blood glucose levels and diabetic ketoacidosis (DKA) that requires immediate medical attention.

What Is Fasting Hyperglycemia?

Insulin is a hormone that carries blood glucose to the cells. When blood glucose rises, the body synthesizes insulin. Glucose binds to insulin and enters the cells, decreasing blood sugar levels. Hyperglycemia (high blood glucose) occurs when the body produces little or no insulin or produces insulin that doesn't function properly.

Therefore, fasting hyperglycemia can be an indicator of prediabetes, diabetes, or gestational diabetes. This can also be seen in people with poor blood glucose management. However, there could be other causes behind fasting hyperglycemia, such as hyperthyroidism, pancreatitis, tumors, and physical stress, including trauma, surgery, and heart attacks.²

<div class="pro-tip"><strong>Also Read: </strong><a href=how-long-lower-blood-sugar-spike>How Long Does It Take for Blood Sugar to Go Down? Best Ways</a></a>.</div>

What Causes High Blood Sugar Levels While Fasting?

High blood sugar levels while fasting occur due to hormone fluctuations or conditions that affect blood glucose levels. You may experience high blood sugar levels while fasting for various reasons:³

• ‍The Lack of Insulin: Hormones have a natural rhythm, meaning they follow a pattern throughout the day. Due to hormonal changes, blood glucose levels rise in the morning. In this case, hyperglycemia can occur because insulin is not present to lower the natural increase in blood glucose levels. 
  • Cortisol and growth hormones naturally rise in the morning, causing the liver to produce glucose. This helps the body have energy upon waking up. Then, increased glucose levels stimulate the pancreas to produce insulin. However, in prediabetes and diabetes, blood sugar stays high due to a lack of insulin. This is called the dawn phenomenon.‍
• ‍Decreased Insulin Release Overnight: People with diabetes are often prescribed insulin using varying methods, timing, and dosages based on individual parameters. External insulin is given to compensate for the body's lack of insulin. In some cases, medication may not fulfill its purpose perfectly. 
  • An example is insulin levels dropping overnight due to improper insulin dosages, such as a low dose of long-acting insulin or insufficient insulin release from an insulin pump. When insulin levels are insufficient, blood glucose rises, causing hyperglycemia. In addition to insulin dose, many factors affect the medication's efficiency, so that adjustments may be necessary.‍
• Overnight Hypoglycemia (Low Blood Glucose Levels): If you miss dinner, your blood glucose levels can drop going into the night. This could also happen if you take more insulin than needed after eating. As a result, not eating or having too much insulin causes your blood glucose to stay low overnight. The body then releases glucose to bring blood glucose levels back to normal, which can cause hyperglycemia. This is called the Somogyi effect.‍
• Other Conditions: Many other conditions can cause fasting hyperglycemia, including but not limited to chronic pancreatitis, tumors, cystic fibrosis, hormonal conditions, and physical stress, such as trauma, surgery, and heart attacks.

10 Fasting Hyperglycemia Symptoms

Hyperglycemia can cause symptoms such as:⁴

• Frequent urination
• Excessive thirst 
• Feeling tired or weak
• Headaches
• Blurred vision
• Weight loss
• Slow wound healing 

Fasting hyperglycemia can also lead to a severe health condition called diabetic ketoacidosis (DKA). DKA symptoms include:^{1, 4}

• Fruity-smelling breath
• Difficulty breathing (shortness of breath)
• Rapid heartbeat
• Nausea or vomiting
• Abdominal pain
• Confusion

Hyperglycemia should be taken under control because chronic hyperglycemia damages tissues over time. It can cause retinopathy (eye damage), nephropathy (kidney damage), neuropathy (nerve damage), gastroparesis (stomach damage), heart disease, and stroke.

Fasting Blood Sugar Test

Testing for diabetes involves measuring fasting glucose levels after an overnight fast of at least 8 hours. This test is used both for screening for diabetes and for monitoring blood glucose levels in people who already have diabetes.⁵ 

Test results indicate:

• Normal Blood Glucose Levels: Less than 100 milligrams per deciliter (mg/dL)
• Prediabetes (Also Called Insulin Resistance): 100–125 mg/dL
• Diabetes: Higher than 125 mg/dL

If your blood glucose test results are high, your healthcare provider may request other tests to confirm the type of diabetes. These tests include glycated hemoglobin (HbA1c), oral glucose tolerance tests, and random blood glucose tests.

Other Blood Sugar Tests

People living with diabetes are commonly prescribed insulin along with lifestyle changes such as a healthy and balanced diet and regular exercise. Adjustments will be necessary as a person's response to diabetes medications and other factors can change. That's why regular monitoring is crucial in managing blood sugar levels. 

Healthcare providers can request proper tests and adjust medications, insulin, and nutrition or exercise plans based on results to achieve better glucose management. Some of the tests used for diabetes monitoring include:⁶

Glycated Hemoglobin (Hemoglobin A1c)

Hemoglobin A1c (HbA1c) shows long-term blood glucose levels. It provides an average of the last two to three months' blood sugar levels before testing. The ADA recommends testing HbA1c twice yearly and more often if your levels are high or you’re changing your treatment.

Preprandial and Postprandial Glucose Levels

You can measure your blood glucose levels at home at home (before a meal) and postprandial (1-2 hours after your first bite). This can show how your blood glucose changes depending on fasting and eating. You can measure them with a blood glucose meter (by pricking your fingertip) or a continuous glucose monitor, automatically predicting blood glucose levels all day and night.

American Diabetes Association (ADA) recommends targeting:⁶

• A1C level: Less than 7%
• Preprandial Glucose Level: 80–130 mg/dL
• Postprandial Glucose Level: Less than 180 mg/dL

However, target levels should be individualized, as the organization (ADA) indicates. 

How to Treat High Blood Sugar Levels While Fasting

The treatment of fasting hyperglycemia depends on determining the cause of high blood sugar levels while fasting. Is it due to a lack of insulin, improper medication dosage or timing, nutrition, or other lifestyle factors? Depending on the cause, your healthcare provider can recommend: 

• Changing Medication Type, Dosage, and Timing: Improper insulin type, timing, and dosage can cause fasting hyperglycemia and poor blood glucose control. After testing and assessment, your healthcare provider can advise changing your medication.‍
• Follow a Personalized Nutrition Plan Based on Your Needs: How much you eat affects blood sugar levels. A healthy and balanced nutrition plan can make it easier to use medication properly and contribute to overall health. Therefore, your healthcare provider may advise you to follow certain nutrition plans so your medication can be adjusted to fit your lifestyle or vice versa.‍
• Managing Exercise and Timing for Better Glucose Control: Regular exercise should be part of treatment and nutrition. Movement also affects blood glucose levels, so knowing when to exercise and adjusting the timing with medication and nutrition is key. Your doctor can advise you on the right timing and intensity of exercise for better blood glucose management.‍
• Regularly Checking Blood Glucose Levels: Diabetes treatment should be individualized. This requires having individual data on how your body responds to medication and lifestyle changes. As your doctor advises, you can use a blood glucose meter and visit your healthcare provider regularly. 
  • A continuous blood glucose meter can help collect data on how your blood glucose levels respond to various activities. This can make it easier to identify potential changes that can improve diabetes management.‍
• Educating Yourself on Blood Glucose Management: Even if your blood glucose is under control, you may experience hyperglycemia in unusual situations, such as sickness or a cold. Knowing how your blood glucose can change based on your actions or situations can help you take preventive measures beforehand.

You should consult your healthcare provider for proper treatment of fasting hyperglycemia. They can order tests and guide you through the appropriate treatment and lifestyle changes.

Learn More About Signos’ Expert Advice

Diabetes management involves proper medication and lifestyle factors (nutrition, exercise, stress, sleep) that vary from person to person. Therefore, finding medication, nutrition, and exercise tailored to your needs can improve blood glucose control. Signos’ experts can provide different solutions to help you choose the best ones for yourself.

A continuous glucose monitoring system (CGM) provides your blood glucose levels throughout the day. Your healthcare provider can see factors affecting your blood glucose levels: medication, nutrition, sleep, exercise, stress, and so on. This can help you choose the proper medication, doses, and personalized lifestyle interventions for you.

Learn more about diabetes management by following Signos' blog. Take a quick quiz to determine if Signos is a good fit for you. 

<div class="pro-tip"><strong>Learn More: </strong><a href=average-glucose-ranges>What Are Normal Glucose Levels for People Without Diabetes</a>.</div>