Why Should I Know My Blood Sugar Levels? - British Heart Foundation

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Blood sugar levels: what is normal?

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Understand health Blood sugar levels: what is normal?

Mark Kearney, BHF Professor of Cardiovascular and Diabetes Research at the University of Leeds, explains why it is important to know your blood sugar numbers. Normal blood sugar levels are between 4.0 and 5.4 mmol/L when fasting, and up to 7.8 mmol/L 2 hours after eating.

by Professor Mark Kearney Page updated: 17 December 2024

by Professor Mark Kearney Page updated: 17 December 2024

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What are blood sugar levels?

We all need some sugar in our blood called glucose, to provide our cells with energy. We get glucose from the food and drinks we consume.

After we eat, a hormone called insulin briefly rises in the body. Insulin helps the body to absorb glucose from the blood, so it can be used as energy. 

Your blood sugar levels, also known as blood glucose levels, are the amount of glucose in your blood.

While the amount can go up and down over the day, there is a blood test (called an HbA1c test) that can measure your average blood sugar levels over about 3 months.

Why do your blood sugar levels matter?

If your body does not have enough insulin to control the sugar from your food and drink, the sugar stays in your bloodstream.

This can also happen if you have insulin resistance, which means your body does not respond to insulin properly.

Over time, high blood sugar levels can damage your blood vessels, leading to health problems such as coronary heart disease, kidney disease and diabetic eye disease.

That’s why it’s important to know if you have high blood sugar, so you can control your levels and reduce the risk of these complications. 

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Should I have my blood sugar checked?

If you're experiencing symptoms of diabetes, talk to your GP about getting tested. Common symptoms include needing to wee a lot, feeling more thirsty, hungry or tired than usual, losing weight without trying to, or blurred eyesight.

If your blood sugar levels are higher than normal but you do not have diabetes, you may not experience any symptoms.

The only way to find out and prevent further health problems is to have a blood test.

If you have coronary heart disease, you will be offered a blood sugar test as part of your routine checks.

If you have a family history of diabetes you will have your blood sugar checked as part of the NHS Health Check in England for people aged 40 to 74, or you can ask your GP.

Similar health checks may also be available in Scotland, Northern Ireland and Wales – check online or via your GP surgery. 

What are normal blood sugar levels?

For most healthy individuals, normal blood sugar levels are: 

When fasting	2 hours after eating
Between 4.0 to 5.4 mmol/L	Up to 7.8 mmol/L

For people with diabetes, blood sugar level targets are as follows:

Type of diabetes	Before meals	After meals
Type 1 diabetes	4 to 7 mmol/L	Under 9 mmol/L
Type 2 diabetes	4 to 7 mmol/L	Under 8.5 mmol/L

If your blood sugar level is too high, your doctor will talk to you about how to reduce it.

How do I reduce my blood sugar levels?

You can reduce your blood sugar levels by following a healthy, balanced diet, which limits added sugars and refined or processed starchy foods and which includes plenty of fruit and vegetables, beans, pulses, lean protein and sources of healthy (unsaturated) fats.

While this will not lower your blood sugar immediately, over time a healthy diet plus regular exercise can lower your blood sugar to a normal level.

• Learn more about eating a healthy, balanced diet.

What is an HbA1c test?

Your GP can test your blood for a substance called HbA1c (glycated haemoglobin), which shows your average blood sugar levels over the last 2 to 3 months.

HbA1c forms when glucose in your blood sticks to red blood cells. Since red blood cells live for up to 3 months, the test shows your average blood sugar levels during that time.

An HbA1c test can be used monitor your blood sugar levels if you're at risk of developing diabetes, or to track blood sugar control if you already have diabetes.

If you have diabetes, an ideal HbA1c level is 48mmol/mol (6.5 per cent) or below.

If you are at risk of developing type 2 diabetes, your target HbA1c level should be below 42mmol/mol (6 per cent).

Should I get a continuous blood sugar monitor?

Blood sugar monitors are devices that track blood sugar levels throughout the day.

They are mainly designed for people with diabetes to help manage their blood sugar levels and maintain a healthy range, which can support better health and wellbeing.

A recent trend involves using continuous blood glucose monitors as part of a 'blood sugar diet', where individuals track how they respond to different foods.

Promoted by some companies, this approach aims to provide personalised dietary recommendations based on real-time glucose data.

While these monitors can provide interesting insights into how your blood sugar levels vary over a day, they are not designed to diagnose issues relating to blood sugar.

For people without diabetes, the benefits of continuous glucose monitoring are less clear, and more evidence is needed.

Blood sugar monitors are not generally recommended for people without diabetes unless suggested by a healthcare professional. If you're curious about your blood sugar levels, it’s best to discuss this with your doctor.  

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