Nearly all of the carbohydrate foods we eat get digested into the simplest form of sugar, called glucose — the body’s main source of energy. (See: What Is Glucose?) When glucose enters your bloodstream, it creates a signal that causes your cells to absorb it for energy. (Think of it as the “energy rush” you get after drinking a soda or eating after being hungry for a long period of time.) Having a normal blood glucose level is a key indicator of metabolic health, whereas abnormally high blood glucose levels are often linked to serious health issues — such as cardiovascular disease, diabetes, stroke and kidney disease. But what is a high glucose level, and how do you measure it? If you have or are worried about developing high blood glucose levels — or hyperglycemia, it’s important to be aware of the signs and preventative measures that can help you avoid the unwanted consequences of this common condition.

What impacts blood glucose levels?

Blood glucose levels are impacted by a variety of factors, including genetics, your metabolic and physical health, the amount of sleep you get, how you respond to stress, your level of physical activity and your diet: how much, what and when you eat. 

Our bodies function best when blood glucose stays within a fairly narrow range, and two hormones are responsible for maintaining control of this range: insulin and glucagon. After eating, the carbohydrates in your food break down into glucose and get released into the bloodstream. The rise in blood glucose triggers the pancreas’s beta ( β) cells to release the hormone insulin, which tells the cells throughout our body to absorb the glucose to use it for energy or store it for future use in our muscles or liver as glycogen (long chains of sugar). Any excess glucose is converted to fat and ectopically stored in liver, muscle and adipose tissues. 

What are normal blood glucose levels and how do I measure them?

Blood glucose levels are in constant flux and they’re different for everyone. While blood glucose levels rising and falling throughout the day is normal, experiencing high energy followed by a crash may mean your blood glucose is swinging within too wide of a range. However, having high blood glucose levels does not mean that you have diabetes. (Learn more: The Link Between Blood Sugar and Diabetes.)

There are a few ways to measure blood glucose levels:

• The A1C test measures your average blood glucose level over the past 2 or 3 months. 
• The Fasting Blood Sugar test measures your blood glucose level after fasting (at least 8 hours). The measurement comes out in the form of milligram of glucose per deciliter of blood. 
• The Glucose Tolerance test measures how your body responds to a glucose-heavy drink after a night of fasting. Blood glucose levels are measured before drinking the glucose solution (fasting blood glucose level) and at hourly intervals after consuming the drink. 
• A Random Blood Glucose test measures your blood glucose at any given time, without the need for fasting or drinking a glucose mixture. 
• Continuous Glucose Monitoring (CGM) is an advanced and comprehensive way to be in constant contact with your blood glucose levels. This method uses a wearable device, like we have developed here at January AI, that measures interstitial fluid (where your glucose moves after it has been through your blood vessels and capillaries) and is helpful when you want to understand a more detailed picture of what’s impacting your blood glucose levels throughout the day and night. 

It’s important to speak with a healthcare professional about the normal blood glucose range for you based on your lifestyle and health status. 

Average ranges for diabetes tests for adults

A1C Test

Normal - 5.6% or below

Prediabetes - 5.7%-6.4%

Diabetes - 6.5% or above

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Fasting Blood Sugar

Normal - 99 mg/dL or below

Prediabetes - 100-125 mg/dL

Diabetes - 126 mg/dL or above

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Glucose Tolerance Test

Normal - 140 mg/dL or below

Prediabetes - 140-199 mg/dL

Diabetes - 200 mg/dL or above

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Random Blood Sugar Test

Normal - N/A

Prediabetes - N/A

Diabetes - 200 mg/dL or above

NOTE: Results for gestational diabetes can differ.

Source: American Diabetes Association

If you are monitoring your interstitial glucose levels daily with a CGM, what’s “normal” will vary. You will have targets for where you want your glucose levels to be in the morning and at night, plus after you eat. Healthcare providers refer to this as time in range, or TIR: Those without prediabetes or diabetes, who are aiming for optimal metabolic health, would try to stay within a range of 70 to 140 mg/dl for as much of the day as possible. People with diabetes might give themselves a bit more wiggle room, aiming for a high percentage of the day in a range of 70 to 180 mg/dl. Keep in mind: These are just targets, so they aren’t personalized to your specific situation. You should always consult with a medical professional about the right TIR goals for you, which can shift for a variety of reasons, including if you’re pregnant, older, or at high-risk for complications.

What are the symptoms of high blood glucose levels?

The symptoms of high blood glucose levels, include:

• Excessive hunger and/or thirst
• Vomiting
• Headaches 
• Blurred vision
• Rapid heartbeat
• Frequent urination
• Fatigue
• Weight loss
• Stomach pain

What are the symptoms of low blood glucose levels?

While the focus of this article is high blood glucose, the opposite can happen too. Much less commonly, too low a level of blood sugar, a condition called hypoglycemia, can be caused by the presence of too much insulin or by other hormone disorders or liver disease. Symptoms may include:

• Lightheadedness
• Dizziness
• Sweating
• Confusion
• Anxiety
• Rapid heartbeat
• Pale skin
• Fainting
• Tingling lips

What causes high blood glucose levels?

There are a handful of risk factors and lifestyle behaviors that can contribute to high blood glucose levels, including:

• Current or a family history of type 2 diabetes
• Gestational diabetes (diabetes during pregnancy)
• African American, Native American, Hispanic or Asian American heritage
• Above-average weight
• High blood pressure or high cholesterol
• Polycystic ovarian syndrome (PCOS), an endocrine condition (i.e. Cushing syndrome), or pancreatic disease.
• Use of a medication that can have a poor effect on your glucose levels: steroids, diuretics, improper dosage of insulin or oral diabetes medication.
• Physical stress (surgery, trauma, an infection, the flu, a virus, etc)
• Lack of exercise and physical activity
• Emotional stress

Are high blood glucose levels dangerous?

High blood glucose levels can be dangerous. If untreated, persistently high glucose levels can be a “silent killer” and increase your risk of type 2 diabetes and infections; hinder your ability to heal wounds; and damage organs, tissues, nerves and blood vessels — which can lead to heart attack, stroke, toxin buildup in the blood, eye and kidney damage. These consequences can have a domino effect and can lead to other cardiovascular and metabolic issues. 

How do you keep your blood glucose at a healthy level?

Maintain a healthy weight and eat well: Eating a colorful and varied diet of mostly vegetables, legumes, lean meats and fruits is important for all aspects of health. Eating smaller portions more frequently may help your blood glucose levels stabilize. Smaller amounts of food require less insulin to be released. High-fiber foods are also particularly beneficial for overall metabolic health and blood glucose management. There are tools that can show you what foods are more harmful to blood sugar than others. The glycemic index (GI)  was developed to show how certain foods affect your blood sugar levels. When your blood glucose levels are too high, aim for foods with low or medium GI values, such as whole grains, fish, yogurt, sweet potatoes, most nuts and legumes. Another tool, glycemic load (GL), tells you how quickly a food causes glucose to enter the bloodstream and how much glucose you’ll get per serving. The international database created by researchers at the University of Sydney in Australia allows you to check both GI and GL.

Exercise: Consistent physical activity (unless your healthcare provider advises against it) can lower your blood glucose levels and reduce the risk of type 2 diabetes by up to a staggering 50%. Exercise has been shown to improve insulin sensitivity and glycemic control, while reducing the risk of mortality, according to a consensus paper published by the American Diabetes Association.

Mind your sleep hygiene: Get the recommended 7 hours/night.

Hydrate: Drinking more water helps remove the excess sugar through your urine. 

Limit alcohol: Alcohol disrupts your body’s process of using glucose for energy and it can negatively impact your blood glucose levels, whether they’re too high or too low.

What can you do if your blood glucose spikes to a high level?

The American Diabetes Association suggests keeping your blood glucose level below 130 mg/dL before a meal and under 180 mg/dL after eating. Most importantly, you’ll want to make sure your blood glucose level isn’t above the target range set by your doctor. (A blood glucose target range can vary from person to person and the time of day.) If your blood glucose level does veer above your upper limit, exercise and hydration can help lower your blood glucose level; however, there aren’t any foods that have the ability to lower blood glucose fast. In the event of a persistent elevated blood sugar level of 300 mg/dL, call your medical provider.

Key takeaways

Blood glucose levels are impacted by a variety of factors, outlined in this report. If untreated, persistently high glucose levels can result in a number of medical problems. If you’re concerned about your blood glucose levels, talk with your medical provider. You can monitor your interstitial glucose with a CGM and outline a plan to better manage your levels with a combination of nutrition and other lifestyle modifications.