WHAT IS GLUCOSE? ITS ROLE IN THE BODY

29/11/2021

Glucose is a simple sugar and the body's main energy source. This article explains what glucose is, its role, blood glucose levels and when to see a doctor

Glucose is a simple sugar and the body’s main source of energy; keeping blood glucose steady is the foundation of good health.

What is glucose? It is a simple sugar found in fruit and honey, and it is produced when the body digests starch. This article explains what glucose is, its role in the body, blood glucose levels and when to see a doctor.

In this article

Quick summary
What is glucose?
The role of glucose in the body
Blood glucose levels
What does long-term high blood glucose do?
When to see a doctor and get tested
Frequently asked questions

Quick summary

• Glucose (C6H12O6) is a monosaccharide, also called a simple sugar or dextrose.

• It is the main source of energy for cells, especially the brain and muscles.

• A normal fasting blood glucose is about 3.9 – 5.5 mmol/L.

• Blood glucose that stays too high or too low affects health; diagnosis is made by a doctor.

What is glucose?

Glucose is a monosaccharide with the molecular formula C6H12O6. It is the simplest sugar the body can absorb directly into the blood. Plants make glucose through photosynthesis from water, carbon dioxide and sunlight.

Glucose occurs naturally in foods such as ripe fruit and honey. Starch is actually a long chain of glucose molecules, while table sugar (sucrose) is one glucose molecule joined to one fructose molecule. When we eat, digestive enzymes break these chains down into glucose for the body to use.

The role of glucose in the body

• Energy supply: cells burn glucose to release energy, water and carbon dioxide.

• Fuel for the brain: glucose is the brain’s main energy source, so the body works to keep blood sugar steady.

• Energy storage: glucose that is not used right away is stored as glycogen in the liver and muscles, ready to be released when needed.

• Hormone control: insulin helps move glucose from the blood into cells, while other hormones help release glucose when blood sugar falls.

Blood glucose levels

Blood glucose is the amount of glucose in the blood and it changes throughout the day. The table below shows commonly used reference levels, measured after fasting for at least 8 hours unless noted otherwise.

Normal (fasting)

3.9 – 5.5 mmol/L (about 70 – 99 mg/dL)

Prediabetes (fasting)

5.6 – 6.9 mmol/L (about 100 – 125 mg/dL)

Diabetes (fasting)

7.0 mmol/L (126 mg/dL) or higher, confirmed by a repeat test

Diabetes (2 hours after an oral glucose test)

11.1 mmol/L or higher

Random blood glucose at any time

11.1 mmol/L or higher should be assessed by a doctor

HbA1c

6.5% or higher is a diagnostic threshold for diabetes

Low blood sugar

Below 3.9 mmol/L (70 mg/dL); needs prompt treatment

These levels are for reference only and do not replace a doctor’s diagnosis or advice. Diabetes must be diagnosed through tests and assessment by a healthcare professional.

What does long-term high blood glucose do?

According to medical sources, when blood glucose stays high over a long period, small blood vessels and nerves can be damaged over time. Possible effects include:

• Eye damage that reduces vision;

• Reduced kidney function;

• Nerve damage, causing numbness, pain or reduced sensation in the hands and feet;

• A higher risk of heart and blood vessel disease;

• Wounds that heal slowly and are prone to infection.

That is why early detection and proper control of blood glucose matter. Any treatment decision should follow a doctor’s guidance.

When to see a doctor and get tested

• Frequent thirst, frequent urination, lasting tiredness or unexplained weight loss;

• Blurred vision or wounds that heal slowly;

• Blood glucose results outside the normal range;

• Risk factors such as being overweight or having a family member with diabetes; regular checks are advised according to your doctor.

Frequently asked questions

Is glucose a sugar?

Yes. Glucose is a simple sugar (monosaccharide). Ordinary table sugar is sucrose, made of one glucose molecule and one fructose molecule.

What is a normal blood glucose level?

For a fasting measurement, the normal range is about 3.9 – 5.5 mmol/L (about 70 – 99 mg/dL). Specific results should be assessed by a doctor.

What blood glucose level indicates diabetes?

A fasting blood glucose of 7.0 mmol/L (126 mg/dL) or higher, confirmed by a repeat test, is one of the diagnostic criteria. There are also criteria based on the oral glucose tolerance test and HbA1c.