Anna Evans

Blood Glucose: What Is It and Why It Is Important

Glucose is your body’s fuel, but you don't want too much of it in the blood. Read the article to learn all about blood sugar levels.


Glucose plays a key role in keeping the body in perfect working order. It’s essential for metabolic processes, such as providing energy to cells. You may know blood glucose by another name – blood sugar.

If you are a healthy adult person with a blood volume of 5 L (1.3 gallons) there is about a teaspoon of sugar in your bloodstream. Although this seems low, your body knows exactly how much it needs and regulates it through complex processes. When your glucose levels are well controlled, they often go unnoticed. However, when glucose levels fall too low or rise too high, the daily functioning of the body can be affected. Let’s learn how the system works and how you can help your hardworking body maintain normal levels of glucose.

Glucose: A fuel for all your cells

Glucose is the simplest type of carbohydrate – a monosaccharide, which means ‘one sugar’. It is the key source of energy for our organs, particularly for the brain and muscles. Glucose is carried by the bloodstream to the cells, where it is transformed into different substances and used for energy just like fuel.

People can get glucose from sources of complex and simple carbohydrates. It is also produced by the body. When your bloodstream has more than enough glucose the excess can also be stored for later use.

There is a glucose factory in your body: your liver

Your liver is one of the main organs involved in the production and regulation of glucose in the body. The liver has the ability to produce glucose from a variety of sources, including amino acids (the building blocks of proteins), lactate, and certain fats. This process, called gluconeogenesis, is important for maintaining normal blood glucose levels, especially during periods of fasting or when the body’s carbohydrate stores are low.

In addition to producing glucose, the liver also stores glucose in the form of glycogen, a complex carbohydrate that can be broken down and converted back into glucose when the body needs additional energy.

Two ‘General managers’ of blood glucose

Imagine your inner organs as factory workers – your hormones would be their managers. These chemical bosses use their own signals to order different organs to raise or lower levels of glucose in your body. Blood sugar levels are regulated by several hormones, the main two are insulin and glucagon. Both of them are produced by the pancreas.

Glucose & Glucagon

When blood glucose levels are low, the pancreas releases a hormone called glucagon. This happens, for example, when you’re exercising and your muscles need more energy than usual. Glucagon targets your liver to break down stored glycogen and release glucose into the bloodstream. This way your body gets the amount of energy it needs.

Glucagon can also trigger gluconeogenesis in the liver so it can produce new glucose from proteins or other chemicals.

Glucose & Insulin

The opposite in effect to glucagon, insulin helps to lower blood sugar levels.

When you eat foods that contain carbohydrates, your body breaks down the carbohydrates into glucose, which is absorbed into the bloodstream. As blood glucose levels increase, the pancreas senses it and releases insulin. Insulin targets the liver and muscles to absorb glucose from the blood. When this happens liver stores glucose molecules in the form of glycogen and the muscles take up the glucose for energy. Then blood sugar levels get back to normal.

If the body does not use glucose for energy but keeps getting more of it with food, the levels of blood sugar remain chronically high. This causes resistance to insulin signals in muscles and the liver. To keep up with high sugar intake, the pancreas has to produce more and more insulin. Eventually, it wears out and the natural process of controlling blood glucose levels gets damaged. This condition is called type 2 diabetes.

When the pancreas stops being able to produce insulin, the liver or muscles don’t get signals to use up glucose. Because of that, the blood glucose remains high, and a person has to use synthetic insulin. This condition is known as type 1 diabetes.

Not only does insulin regulate glucose levels, but it also serves a pivotal role in the metabolic process of fats and proteins. It encourages protein synthesis while curbing fat breakdowns in body tissue – two crucial aspects to healthy weight maintenance.

Overall, insulin is the essential hormone and when we are monitoring blood sugar levels, we are actually checking if our pancreas works and if insulin being produced properly.

What blood glucose is measured in

There are two ways of measuring blood glucose levels used in different countries: millimoles per liter (mmol/L), which is a standard in the UK, and milligrams per deciliter (mg/dL) – a standard measure for the U.S.

Millimoles per liter (mmol/L) unit is based on the International System of Units and is commonly used in medical laboratories around the world.

Ways to find out your blood glucose level

Measuring blood glucose is an important way to monitor how your insulin works and manage diabetes. It can also be useful for people without diabetes to track their blood sugar levels to help prevent the development of diabetes and other related conditions. Here are some ways to measure blood glucose:

  • Laboratory testing This method involves professionals checking a sample of blood from your vein. Usually, it is recommended to do fasting for at least 8 hours before the test.

  • Self-monitoring blood glucose (SMBG) This method involves using a small device called a glucometer to measure your blood sugar levels at home. The device uses a drop of blood from a finger prick or another part of the body to determine your blood sugar level.

  • Continuous glucose monitoring (CGM) This very recent method involves wearing a small sensor under your skin that continuously measures your blood sugar levels throughout the day and night. The sensor sends the data to a device that displays your blood sugar levels in real-time.

Blood glucose levels – what is normal and what’s not

Blood sugar levels are considered normal when they are within the range of 4.0 to 5.4 mmol/L (72 to 99 mg/dL) before a meal and less than 7.8 mmol/L (140 mg/dL) two hours after a meal.

In people with type 2 diabetes, the body may not use insulin effectively, leading to high blood sugar levels. Blood sugar levels may be consistently high or may fluctuate, sometimes reaching levels above 200 mg/dL (11.1 mmol/L).

In people with type 1 diabetes, the body does not produce enough insulin. As a result, blood sugar levels may be consistently high, often above 200 mg/dL (11.1 mmol/L).

Symptoms of abnormal blood glucose levels

It is very important to monitor your blood sugar, as uncontrolled levels can have serious consequences. Conditions to beware of:

  • Hyperglycemia – high levels of blood sugar in the blood.

Symptoms of hyperglycemia can include increased thirst, frequent urination, fatigue, and blurred vision. In severe cases, high blood sugar can lead to complications such as kidney damage, nerve damage, and blindness.

  • Hypoglycemia – the level of glucose in the blood is low.

Symptoms of hypoglycemia can include dizziness, tremors, sweating, hunger, irritability, and difficulty concentrating. In severe cases, low blood sugar can cause fainting or seizures.

  • Unconscious hypoglycemia – a severe case of hypoglycemia or hypoglycemic coma, is a serious condition in which the level of glucose in the blood becomes dangerously low, leading to unconsciousness.

Symptoms of unconscious hypoglycemia can include difficulty speaking, seizures, and loss of consciousness. If left untreated, unconscious hypoglycemia can be life-threatening.

If you suspect you have problems with your blood sugar, discuss your symptoms with your doctor.

Let’s sum up: why blood glucose is important

Blood glucose is a source of your energy and it can provide insight into your health. Our body can absorb glucose from food, use it as fuel, and store it or produce new glucose in the liver. Glucose levels are controlled by hormones with the main ones being insulin and glucagon. High blood glucose can be a sign of insulin resistance, which may lead to diabetes and other serious health conditions if left unchecked. Low blood glucose can also be a cause for concern as it can lead to lightheadedness, confusion, and other symptoms that affect your day-to-day life. Monitoring your blood glucose gives you the chance to catch any issues early on and take steps to manage them, such as making changes in your diet or lifestyle.

Hungry for knowledge? Here’s more

This simple video by the non-profit organization Khan Academy explains the connections between blood glucose and insulin, and what’s the difference between different types of diabetes.

Healthypedia FAQ

Normal blood sugar levels are typically between 4.0 to 5.4 mmol/L (72-99 mg/dL) before a meal and less than 7.8 mmol/L (140 mg/dL) two hours after a meal.

High blood sugar levels, also known as hyperglycemia, can be caused by a variety of factors, including not taking enough insulin or other diabetes medications, eating too much food or consuming too many high-sugar foods, being inactive for a prolonged period of time, and being stressed or sick.

Low blood sugar levels, also known as hypoglycemia, can be caused by taking too much insulin or other diabetes medications, skipping a meal or not eating enough food, and engaging in intense physical activity without eating enough to compensate.

Symptoms of high blood sugar levels (hyperglycemia) can include increased thirst, frequent urination, fatigue, and blurred vision. Symptoms of low blood sugar levels (hypoglycemia) can include dizziness, tremors, sweating, hunger, irritability, and difficulty concentrating. In severe cases, both high and low blood sugar levels can lead to unconsciousness or seizures.

People with diabetes use insulin pumps to help regulate their blood sugar levels. These devices deliver a continuous supply of insulin to the body through a small tube that is inserted under the skin. In some cases, people with diabetes may need to inject insulin using a needle and syringe.

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