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Hypoglycaemia causes, symptoms and treatment

Hypoglycaemia is the medical term for having low blood sugar. It is a common complication of diabetes but rarely happens in people without the condition. It needs to be treated quickly to prevent it getting worse. Luckily, it is easy to treat yourself. Learn more about the causes, signs and treatment for hypoglycaemia.

Medically reviewed by Dr. Caroline Fontana Written by our editorial team Last reviewed 02-04-2024

What is hypoglycaemia?

Hypoglycaemia, also known as ‘hypo’, occurs when your blood sugar levels become too low. It is specifically when your blood glucose drops below 4mmol/L.

It causes symptoms because your body does not have enough glucose to function properly. This is because glucose is one of your body’s main energy sources.

Sugar cubes representing blood sugar levels dropping.

You can also experience hyperglycaemia, where your blood sugar levels are too high. This can be 7mmol/L before a meal or above 8.5mmol/L two hours after a meal. High blood sugar levels are not harmful short-term, but over time can result in diabetic ketoacidosis (DKA).

What causes hypoglycaemia?

Hypo is a complication of diabetes. It can occur in people with type 1 diabetes and type 2 diabetes.

Hypo can occur:

  • After exercise - your muscles need more sugar to supply more energy which can cause your levels to drop.
  • If you take too much insulin or diabetes medication - this will lower your blood sugar levels.
  • If you miss or delay a meal - your body won’t have enough glucose, especially if you are on diabetes treatment.
  • After drinking alcohol - your liver needs to break down the alcohol, which stops it from releasing glucose into your bloodstream.

These factors can make everyone’s blood sugar levels drop. However because diabetics have a lack of insulin, their blood sugar levels are harder to manage and they experience hypo.

Can you get hypoglycaemia if you don’t have diabetes?

Hypo is rare in people who do not have diabetes.

Sometimes, you can experience reactive hypoglycaemia. This is where your body produces too much insulin after a large carbohydrate-based meal. Experts do not know why this happens, but it is more common in overweight people or in those who have had a gastric bypass.

Some other possible causes include:

  • fasting or malnutrition
  • heavy alcohol consumption
  • severe conditions affecting the thyroid gland, kidneys or liver
  • Addison’s disease - a condition that affects the adrenal glands

Certain medications can also cause hypoglycaemia as a side effect, such as:

You should speak with your doctor if you are worried about the side effects of your medication.

What are the symptoms of hypoglycaemia?

Symptoms of hypo are different for everyone. Possible low blood sugar symptoms include:

  • feeling shaky
  • sweating
  • feeling anxious, confused, irritable or tearful
  • going pale
  • heart palpitations and a fast pulse
  • lips feeling tingly
  • blurred vision
  • feeling hungry
  • tiredness
  • headache
  • difficulty concentrating

Severe hypoglycaemia can cause you to lose consciousness.

If you experience hypoglycaemia while you’re asleep, you may notice your sleep is disturbed. Or, you may only experience symptoms in the morning such as a headache, feeling unusually tired or damp sheets and clothing from sweating.

Close-up of a man testing his blood glucose levels.

If you notice any of these symptoms, you should test your blood sugar levels using your blood glucose monitor.

Hypo unawareness

Hypo unawareness is a phenomenon where you are experiencing hypo without any of the symptoms.

It commonly occurs in people with type 1 diabetes or in those who get hypos very often. According to Diabetes UK, up to 25% of people with type 1 diabetes are unaware of hypos.

25% of people with type 1 diabetes have hypo unawareness.

If you have hypo unawareness, the only way you know you have low blood glucose is to check using a blood glucose monitor.

You can regain your awareness so you should speak to your diabetes team if you think you have hypo unawareness. They may recommend short-term solutions like a continuous glucose monitor (CGM).

Hypoglycaemia vs diabetic ketoacidosis (DKA)

DKA can occur if your blood sugar levels are high for a long time. If you have DKA, you may experience symptoms such as:

  • feeling thirsty
  • needing to pee more often
  • stomach pain
  • feeling or being sick
  • deep breathing
  • fruity-smelling breath
  • feeling tired, sleepy or confused
  • blurred vision

DKA usually affects people with type 1 diabetes, especially children who have not yet been diagnosed with diabetes. It can occur occasionally in people with type 2 diabetes who take insulin.

How do you treat hypoglycaemia?

If you test your blood glucose and your levels are below 4 mmol/L, you will need to treat the hypo immediately.

You should not leave hypo untreated as it can be life-threatening for people with diabetes. Follow these steps to treat low blood sugar.

How to treat hypoglycaemia
Test your blood

1 Test your blood glucose levels.

If your levels are below 4mmol/L, eat or drink

2If your levels are below 4mmol/L, eat or drink something sugary.

Rest for 10-15 minutes

3Rest for 10-15 minutes, then re-test your blood sugar.

blood sugar is still low

4Repeat step 2 if your blood sugar is still low.

eat a long-acting carb

5Once your levels are stable, eat a long-acting carb or your next meal.

For most people with diabetes, you will need to eat or drink 15-20g of a fast-acting carbohydrate. Advice from Diabetes UK suggests eating or drinking one of the following:

  • 5 glucose/dextrose tablets
  • 4 jelly babies
  • 150-250ml of a sugary drink or fruit juice
  • 2 tubes of a glucose gel like GlucoGel
  • glucose juice like Lift Shots

Avoid fatty foods and drinks such as chocolate and milk. They do not contain as much sugar and the sugar they do contain may be absorbed more slowly.

You should rest for 10 - 15 minutes afterwards then re-test your blood sugar. If it is still less than 4 mmol/L, you should consume more fast-acting carbohydrates and re-test after 10 minutes.

Children will need less carbohydrates to treat hypo. If you use an insulin pump, your hypo treatment will be different. Ask your diabetes team for more advice.

How do you treat severe hypoglycaemia?

If someone with hypoglycaemia has become unconscious, they will require different treatment.

You should put them in the recovery position and give them an injection of the hormone glucagon if they have an injection kit. This should be given by a friend or family member who is trained to do it, or by a healthcare professional.

You should ring for emergency services if:

  • they don’t have an injection kit
  • there is no one available who is trained to administer an injection
  • the injection doesn’t work after 10 minutes

Do not give them any food or drink as they can choke.

What should you do after a hypo?

You should eat a slow-acting carbohydrate to prevent your blood sugar levels from dropping again. This could be a:

  • sandwich
  • piece of toast
  • small bowl of cereal
  • glass of milk

You can also eat your next meal if it's due. Ask someone for help if you are feeling too drowsy or unwell to treat hypo yourself.

If you get hypos often, ask your doctor for advice on managing your diabetes.

How do you prevent hypoglycaemia?

Some ways you can prevent and reduce the risk of hypoglycaemia include:

  • taking your diabetes treatments correctly
  • regularly monitoring your blood glucose levels
  • eating extra carbohydrates before or during exercise
  • drinking less alcohol and eating a snack after drinking

Learning the early signs of hypoglycaemia is one of the best ways of treating it. So, you can prevent any severe symptoms. You should also keep some sugary snacks on you or by your bed to treat a hypo as soon as possible.

It may be a good idea to record the details of your hypo, so you can track what triggers low blood sugar levels and help to prevent it in the future.

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