What should a ‘normal’ blood sugar level look like and how is it measured?
Medically reviewed by Dr Louise Wiseman MBBS, BSc (Hons), DRCOG, MRCGP and words by Annie Hayes
People with diabetes struggle to control their blood sugar levels without treatment. If your blood sugar levels are left to stay high for a long period of time then a number of serious complications can arise.
But what should a ‘normal’ blood sugar level look like, how is it measured and what can you do to restore equilibrium when it moves outside the recommended guidelines?
What is your blood sugar level?
Blood sugar is the concentration of glucose in the body, explains Dr Rai, and it’s used for energy. Also known as the plasma glucose level, blood sugar is expressed in millimoles per litre (mmol/l). Normally, levels stay within narrow limits throughout the day: approximately 4 to 8mmol/l.
If your blood levels are too high or too low for long periods of time, it can lead to adverse health conditions.
Not only does glucose come from the food we eat, but the body creates it by digesting foods, such as carbohydrates, into a sugar that circulates in the bloodstream. This is why blood sugar levels are naturally higher after meals and usually lowest in the morning.
High blood sugar symptoms
Symptoms of high blood sugar include the following;
- Feeling very thirstyor hungry or even nausea
- Blurred vision
- Passing urine more often than usual
- Recurrent episodes of infections such as thrush
Low blood sugar symptoms
Low blood sugar symptoms can include feeling;
- a change in mood or easily irritated
- shaky or trembling or feeling palpitations
- problems with concentration
Why control blood sugar levels?
If your blood levels are too high or too low for long periods of time, it can lead to potentially severe health problems, both acute (immediate) and chronic (long term). Acute problems include high and low blood sugar levels or potentially even a comatose state. Chronic problems are varied.
High blood sugar levels
When blood sugar levels rise, the pancreas releases a hormone called insulin, which prompts the cells to absorb sugar from the blood, explains Dr Rai. ‘This causes blood sugar levels to drop and the sugar that isn’t needed to fuel your body right away gets stored in cells to use at a later time.’
To move blood sugar into cells throughout the body, your body needs insulin. ‘If you cannot produce enough, or the insulin does not work effectively, it leaves too much sugar in the blood and not enough in the cells for energy,’ she continues. ‘This leads to high circulating sugar levels in the bloodstream and can lead to diabetes.’
When very high levels of blood glucose are present for years, it leads to damage of the small blood vessels. This affects the circulation of blood around the body. This, in turn, increases your risk of developing late-stage diabetes chronic complications including:
- Retinopathy(eye disease)
- Nephropathy(kidney disease)
- Neuropathy(nerve disease)
- Foot problems can arise from the combination of nerve damage reducing the feeling in the feet and poor circulation preventing wounds healing easily.
- Cardiovascular disease, such as heart attack, hypertension, heart failure, stroke and problems caused by poor circulation, e.g. gangrene in the worst cases.
- Gum disease and other mouth problems (the high sugar encourages bacteria that then increase the acidity in the mouth targeting enamel and gums)
- Sexual problems can arise from reduced sensation and reduced blood flow to the sexual organs.
If you smoke, have uncontrolled high blood pressure or high cholesterol this will exacerbate any diabetic complications with circulation, potentially making them worse. If you take care to control your blood sugar, regulate blood pressure and keep cholesterol under control (with or without medicine), all of these complications can be prevented or lessened.
Low blood sugar levels
Low blood sugar, also known as hypoglycaemia, is what happens when the glucose in your blood drops too low, says Dr Basford. In diabetic patients this is most common if the balance of diabetic medication and activity or food intake has gone awry – such as taking medication then forgetting to eat, or drinking alcohol on an empty stomach. Not all diabetics will have hypos.
Is reactive hypoglycaemia real or fiction?
There is a condition called reactive hypoglycaemia which related to ‘hypos after eating’ that can occur in people with or without diabetes. It is more common in those who are overweight or who have had gastric bypass surgery. This occurs after a large carbohydrate- loaded meal and is thought to be caused by the pancreas releasing too much insulin beyond what is needed for the meal.
After the normal amount of glucose has been taken up the blood sugar level then drops further to a lower than desired level. There are various suggestions as to why this happens (benign tumours of the pancreas producing excess insulin or using too much glucose, or problems with glucagon production – a hormone that normally mobilises glucagon into the bloodstream).
Reactive hypoglycaemia would have similar symptoms to hypoglycaemia but sometimes these symptoms are experienced in people with a normal sugar level. Scientists suggest this is due to delays in digestion and possible other causes. If the sugar is normal but the person experiences symptoms it is called ‘postprandial syndrome’.
If these symptoms regularly happen after eating, a doctor’s opinion should be sought to exclude other causes. General advice is to try the following:
- Eat more frequent, smaller meals
- Eat protein and fibre for balance and healthy digestion
- Do not drink alcohol without eating
- Avoid quick fix sugar like fizzy drinks
How to measure blood sugar levels
To diagnose diabetes and keep track of how well it’s being controlled, there is a laboratory blood test that a doctor can arrange called HbA1c. ‘This gives an average of your blood sugar level over the previous few months so you and your doctor can know if your blood sugar is high most of the time over this period,’ says Dr Basford.
When it comes to monitoring your blood sugar levels at home, there are a few options available. Home testing kits come in a variety of shapes and sizes, and a pharmacist or the diabetes clinic nurse can advise you about the best model. Usually, this will involve a finger prick test.
‘A finger prick test is the most well known and widely used method,’ says Dr Basford. ‘Some people with diabetes will have to do this every day for example if you are using certain diabetic medicines like insulin or sulphonylureas’.
Alternatively you may wish to use a flash glucose monitor. ‘This device sits on your skin and can determine your blood sugar levels,’ says Dr Basford. ‘This is said to work very well and means you don’t have to do a finger prick every time you check your levels.’
Flash glucose monitors measure the sugar in the fluid surrounding your cells called the ‘interstitial fluid’, rather than in the actual blood. Because of this there can be a delay in this reading falling as your actual blood sugar falls, so it is advised to still use the finger prick method from time to time if the reading is low, if you think you might be having a drop in your blood sugar or if you don’t feel well.
Not everyone with diabetes needs to check their levels so frequently. Always take the advice of your healthcare team. You will also be advised what to do should you become generally unwell or have warnings of low or high sugar levels. You may only learn this by testing regularly when you are newly diagnosed, so you and the medical team can begin to predict which symptoms mean a change in sugar levels in you.
❗ If you are diagnosed with diabetes ask your diabetic nurse or doctor to explain how and when to test your blood sugar. Some meters are available to some patients on prescription, if you buy your own meter the strips may not be in prescription.
What should glucose levels be?
The ideal blood glucose values are:
- 4 to 7mmol/l before meals
- Less than 9mmol/l around 2 hours after a meal
- Around 6 to 9mmol/l at bedtime
There are differing opinions about the ideal blood glucose level range and your diabetes team can give you individual advice on the range to aim for. For diabetic patients the target blood sugar at one and two hours after a meal may be more stringent than the above.
How often should blood glucose levels be measured?
Not all people with diabetes have to check their blood sugars themselves, says Dr Basford. ‘If you’re using insulin or sulphonylurea medications, your doctor or nurse will give you a plan to follow so you know when you should be checking.’
This usually depends on when you’re taking your medication, when you’re having meals and also if you’re feeling unwell. It also depends on your lifestyle – the needs of a PE instructor will be different to someone who sits at a computer all day.
Generally, people who have type 1 diabetes – or have type 2 diabetes that’s being treated with insulin – ought to measure their blood sugar levels daily before meals. Some days one or two tests can be done, while on others four or five might be needed.
If you have type 1 diabetes and have more than 20mmol/l of glucose in your blood, you should use a urine strip to check for the presence of ketones. If ketone bodies are present, it’s a warning sign of diabetic acidosis, and you should consult your doctor immediately.
People with type 2 diabetes should measure their blood glucose levels once or twice a week – either before meals or 90 minutes after a meal – and complete 24-hour profile once or twice a month. This means measuring glucose levels before each meal.
However, for elderly people and those with other medical problems, it’s often enough to check the urine for glucose – usually before breakfast and the evening meal. This is because cardiovascular complications such as heart attacks, stroke and angina are the main cause of serious illness and death in people with type 2 diabetes.
They can do this by:
- Controlling blood pressure more rigorously
- Lowering cholesterol levels with medication
- Increasing or starting exercise
- Stopping smoking
Tips for healthy blood sugar levels
There are many factors that may affect your blood sugar levels. These can vary from a lack of exercise, being unwell, eating high-sugar foods, and even stress, says Dr Basford. Luckily, lifestyle changes can help keep your blood sugar levels healthy.
If you have high blood sugar levels Dr Basford suggests the following:
- Exercise more regularly.
- Avoid foods that are high in sugar or carbohydrates.
- Keep on top of any diabetes medication.
- Regularly check your levels if you’ve been told to do so by your doctor.
Whereas if you are suffering from a drop in your blood sugar levels, she suggests the following:
- Drink a fizzy drink or fruit juice.
- Eat a small handful of sweets.
- Try piece of toast with spread, or a glass of milk.
‘If you have diabetes, test your blood sugar levels again 15 minutes after eating; you should be looking for a reading of 4mmol or higher,’ adds Dr Basford. ‘If this is happening often, speak to your doctor as your diabetes medicines might need to be changed.’