Hypoglycaemia means an abnormally low level of sugar (glucose) in the blood. When your glucose level is too low, your body does not have enough energy to carry out its activities. This is described as a 'hypo'.

Hypoglycaemia is most commonly associated with diabetes, and mainly occurs if someone with diabetes takes too much insulin, misses a meal, or exercises too hard. Some diabetes treatments, such as certain tablets, can also cause hypoglycaemia.

People who do not have diabetes can also experience hypoglycaemia, although this is much rarer. It can be triggered by malnutrition, binge drinking or certain conditions, such as Addison’s disease.

Read more about the causes of hypoglycaemia.

What are the symptoms of hypoglycaemia?

Most people will have some warning that their blood glucose levels are too low, which will give them time to correct them. Symptoms usually occur when blood sugar levels drop under 4 millimoles per litre (mmol).

Typical early warning signs are feeling hungry, trembling or shakiness and sweating. In more severe cases there can also be confusion and difficulty concentrating.

It is also possible for hypoglycaemia to occur during sleep, which can cause excess sweating, disturbed sleep and feeling tired and confused upon waking.

Read more about the symptoms of hypoglycaemia.

Correcting hypoglycaemia

The immediate treatment for a hypo is to have some food or drink that contains sugar (such as chocolate, sugar cubes or fruit juice) to end the attack. After having something sugary, you may need to have a longer-acting carbohydrate food, such as a few biscuits or a sandwich, depending on which insulin you are using.

A hypo is often confused with having too much sugar in the blood, which is called hyperglycaemia. If you are not sure whether someone has hypoglycaemia or hyperglycaemia, always give them food containing sugar, such as a chocolate bar or a glass of fruit juice. As long as they are fully conscious, it will do them no harm.

If hypoglycaemia is not treated, it may lead to unconsciousness because there is not enough glucose for normal brain function. At this stage, an injection of the hormone glucagon can be given to quickly raise blood glucose levels and restore consciousness.

Read more about how hypoglycaemia is treated.

Preventing a hypo

If you have diabetes, the safest way of avoiding a hypo is to keep a regular check on your blood sugar and know how to recognise the early symptoms. Make sure you eat regularly and limit your alcohol intake. It is also important to eat some form of carbohydrate before exercising.

Always carry with you dextrose tablets, a carton of fruit juice (one that contains sugar), or a chocolate bar in case you feel symptoms coming on or you detect a low level on your glucose-testing meter.

Make sure your friends and family know about your diabetes and the risk of hypoglycaemia. It may also help to carry some form of identification that lets people know about your condition in an emergency.

When hypoglycaemia occurs due to an underlying condition other than diabetes, the condition will also need to be treated to prevent a further hypo.

Read more about how to prevent hypoglycaemia.

The symptoms of hypoglycaemia usually begin when a person's blood glucose level drops below 4 millimoles per litre (mmol).

Most people will experience some early warning symptoms, although some people with diabetes can experience sudden or severe hypoglycaemia.

The symptoms may vary from person to person and it is important to be aware of the early warning signs so that you can treat them. Read more about how hypoglycaemia is treated.

Early signs

The early warning signs of mild hypoglycaemia may include:

• feeling hungry
• sweating
• dizziness
• tiredness (fatigue)
• blurred vision
• trembling or shakiness
• anxiety or irritability
• going pale
• fast pulse or palpitations
• tingling of the lips

Signs of more severe hypoglycaemia include:

• difficulty concentrating
• confusion
• disorderly or irrational behaviour, which may be mistaken for drunkenness

Nocturnal hypoglycaemia

Having a hypo while you’re asleep is known as nocturnal hypoglycaemia and is more common in people who treat diabetes with insulin. You will often only notice the symptoms when you wake up in the morning. The symptoms can include:

• headache
• disturbed sleep
• feeling unusually tired in the morning
• damp sheets or clothing from sweating

In most cases hypoglycaemia occurs in people with diabetes, although in rarer cases it can occur due to other underlying conditions.

Causes of hypoglycaemia in people with diabetes

Overdose of diabetes medication

A common cause of hypoglycaemia is taking too much insulin medication for your current needs.

A drop in blood glucose levels can also happen when you take too much oral hypoglycaemia medication, such as sulphonylurea, which causes a release of insulin. This medication is often used in treating type 2 diabetes to lower blood glucose.

Exercise, food and alcohol

For people with type 1 diabetes, maintaining the correct blood glucose level involves balancing between the amount of insulin you inject, the amount of food you eat and the amount of energy you burn during exercise.

Hypoglycaemia may occur if you have taken your dose of insulin as usual but your carbohydrate intake is lower than normal, or has been used up more quickly. This may happen if you delay or miss a meal or snack, do not eat enough carbohydrate, or do more exercise than usual.

Hypoglycaemia may also occur in people with diabetes who have been drinking alcohol on an empty stomach, without food.

Causes of hypoglycaemia in people without diabetes

Hypoglycaemia (even mild cases) is very rare in people who are not on insulin or sulphonylurea. The possible causes of hypoglycaemia in people without diabetes are outlined below.

Reactive hypoglycaemia

Too much insulin in the blood in people without diabetes type 1 is commonly caused by their pancreas producing too much insulin after a large carbohydrate-based meal. This is known as reactive hypoglycaemia. The reason for it is not clear, although it is thought to be more common in people who are overweight or have had gastric bypass surgery, and those with type 2 diabetes.

In rare cases, a benign (non-cancerous) tumour in the pancreas may cause an overproduction of insulin, or the tumour itself may use up too much glucose.

Other health conditions

Other possible causes of hypoglycaemia in non-diabetics are:

• fasting or malnutrition – you are not consuming enough nutrients for your body to function properly
• binge drinking or heavy drinking of alcohol
• Addison's disease – a disorder of the adrenal glands
• certain medication – hypoglycaemia has been known to occur in people taking quinine (for malaria), salicylates (for rheumatic disease) and propranolol (for high blood pressure)
• severe illnesses affecting the liver, kidneys or thyroid gland

In most cases, hypoglycaemia can be self-treated when you recognise the symptoms of a hypo. If there is an underlying condition causing regular hypos, this will need to be diagnosed and treated.

Treating an episode of hypoglycaemia

The immediate treatment for a hypo is to have some sugary food or drink to end the attack.

For example, try:

• a glass of fruit juice (that contains sugar) or Lucozade
• a few sugar lumps
• a handful of sweets
• three or more glucose tablets
• a cup of milk
• half a cup of non-diet soft drink

After having something sugary, you should have a longer-acting carbohydrate food, such as a few biscuits, a cereal bar, a piece of fruit or a sandwich.

You should measure your blood sugar again 15 minutes later and if it is still too low (below 4 mmol), then have some more sugary food or drink and test it again in another 15 minutes.

If you cannot treat your hypo because it is more severe, someone else can help you by applying Glucogel (or honey, treacle or jam) to the inside of your cheeks and gently massaging the outside of your cheeks. It may take 10-15 minutes before you feel better.

If you are having several episodes of hypoglycaemia a week you should contact your GP to find out the underlying cause. You may need your medication adjusted, or there may be another condition causing hypoglycaemia that needs treating.

If a person is unconscious

If a person is already unconscious due to a severe hypo, they need to be put into the recovery position and given an injection of the hormone glucagon, which raises the blood glucose level.

The injection is best done by a friend or family member who knows what they are doing, or a trained healthcare professional.

If there is no-one trained to give the injection, call 999 for an ambulance immediately. Never try to put food or drink into the mouth of someone who is unconscious, as they could choke.

If you have diabetes, try to stick to your medication plan and also eat regular meals to help prevent hypoglycaemia. It is important to monitor your blood sugar (glucose) levels.

Monitoring your blood glucose

The safest way of avoiding a hypoglycaemic attack is to keep a regular check on your blood sugar, and knowing how to recognise the early symptoms.

You can monitor your own blood glucose levels using a simple finger prick test or a urine test.

Eat regularly and limit alcohol

Generally, people with hypoglycaemia should eat regularly and not miss meals.

If you have reactive hypoglycaemia, you will need to include in your diet lots of complex carbohydrates (such as potatoes, rice and pasta) but make sure you eat smaller amounts more frequently to avoid a sudden surge of insulin in your blood.

Alcohol can affect your body's ability to release glucose. If you have type 1 diabetes, you are advised to drink no more than 2-3 units of alcohol a day, and to eat a snack after drinking alcohol.

Make sure you eat some form of carbohydrate before and after you do any exercise.

Be prepared and make others aware

Parents of children with type 1 diabetes can often quickly recognise the symptoms, but children should carry with them at all times a carton of fruit juice (that contains sugar) or a chocolate bar, in case they feel the symptoms coming on. If you have type 1 diabetes, you should carry glucose gel or some sugary food with you at all times.

Tell your friends and family about your condition, how to spot the signs of a hypo, and how to treat it. People with diabetes are advised to carry a form of identification with them that states their condition, so that they can be helped quickly and efficiently.

Preventing nocturnal hypoglycaemia

It is important to avoid recurrent hypoglycaemia during the night as this can lead to reduced warning of daytime hypos. You may sleep through these, but wake up feeling like you have a hangover. Try:

• keeping something sugary by your bedside
• having a snack before bedtime, such as biscuits and milk
• checking your blood glucose levels between 3am and 4am when hypos are most likely to happen

Hypoglycaemia and driving

As hypoglycaemia can cause confusion, drowsiness, or even unconsciousness, this can present a significant risk to you or other road users. If you are taking insulin, or are at risk of hypoglycaemia, you should test your blood sugar before driving and at regular intervals while driving.

If your blood sugar is low, then hypoglycaemia should be treated and your blood sugar retested before driving. If you have problems with recurrent hypoglycaemia, or hypoglycaemia unawareness, then you should inform your diabetes specialist. You may have to inform the DVLA.