Hypoglycaemia (low blood sugar)

Hypoglycaemia, often called a "hypo", means the level of glucose in your blood has dropped too low (less than four millimoles per litre). Glucose is sugar, and when there isn't enough of it, your body doesn't have the energy it needs to carry out its activities.

Hypoglycaemia is most often linked with diabetes. It mainly happens when someone with diabetes takes too much insulin, misses a meal or exercises too hard.

Rarely, a person who doesn't have diabetes can also get hypoglycaemia. Malnutrition, binge drinking or certain conditions, such as Addison's disease, can trigger it.

Most people get some warning that their blood sugar is too low, and that gives them time to put it right. Symptoms of hypoglycaemia usually begin when blood sugar falls below four millimoles (mmol) per litre.

The early warning signs are typically feeling hungry, trembling or shakiness, and sweating. If it gets worse, you may feel confused and find it hard to concentrate. In very severe cases, a person with hypoglycaemia can lose consciousness.

It can also happen while you sleep. When it does, you may sweat a lot, sleep badly, and wake up feeling tired and confused.

The immediate treatment for hypoglycaemia is to have something sugary to eat or drink, such as dextrose tablets or fruit juice. This brings your blood glucose levels back to normal.

After that, you may need a longer-acting "starchy" carbohydrate food, such as a sandwich or a few biscuits.

If hypoglycaemia makes someone lose consciousness, an injection of the hormone glucagon can be given to raise blood glucose levels and restore consciousness. This only applies if an injection is available and the person giving it knows how to use it.

You should dial 999 to request an ambulance if:

• a glucagon injection kit isn't available
• there's nobody trained to give the injection
• the injection is ineffective after 10 minutes

Never try to put food or drink into the mouth of someone who's drowsy or unconscious, because they could choke. This includes some of the high-sugar preparations made for smearing inside the cheek.

If you have diabetes that needs treatment with insulin, the safest way to avoid hypoglycaemia (low blood sugar) is to check your blood sugar regularly and learn to recognise the early symptoms.

Missing meals or snacks, or eating less carbohydrate than planned, can raise your risk of hypoglycaemia. Be careful with alcohol too. It can also cause hypoglycaemia, sometimes many hours after you've been drinking.

Exercise or activity is another possible cause, so you should have a plan for it. That could mean eating carbohydrate before, during or after exercise, or adjusting your insulin dose.

Change the place where you inject insulin regularly, because the amount of insulin your body absorbs can differ depending on where it's injected.

Always carry rapid-acting carbohydrate with you, such as glucose tablets, a carton of fruit juice (one that contains sugar), or some sweets. You'll then have something to hand if you feel symptoms coming on or your blood glucose level is low.

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 tells people about your condition in an emergency.

When hypoglycaemia is the result of an underlying condition other than diabetes, that condition needs to be treated to prevent another hypo.

Hypoglycaemia, or low blood sugar, usually starts to cause symptoms when your blood glucose level drops below four millimoles (mmol) per litre.

If you have diabetes, particularly if you're treated with insulin, you may be advised to use a small device called a blood glucose meter to check your blood glucose levels regularly.

Symptoms can differ from one person to another, so it helps to know the early warning signs and treat them when they appear. Signs and symptoms of hypoglycaemia can include:

• feeling hungry
• sweating
• dizziness
• tiredness (fatigue)
• blurred vision
• trembling or shakiness
• going pale
• fast pulse or palpitations
• tingling lips
• irritability
• difficulty concentrating
• confusion
• disorderly or irrational behaviour, which may be mistaken for drunkenness

If hypoglycaemia isn't treated promptly and your blood glucose levels fall low enough, you may become drowsy or even lose consciousness.

Most people with insulin-treated diabetes find that the symptoms of hypoglycaemia change and become less obvious the longer they live with the condition. For some, the warning symptoms become greatly reduced. That puts them at significant risk of severe episodes, where they depend on others for help.

Let your diabetes care team know if this happens to you, because your treatment may need to be changed to reduce the risk.

Read more about how hypoglycaemia is treated

Having a hypo while you're asleep is called nocturnal hypoglycaemia. It's more common in people who treat diabetes with insulin.

Some people find their sleep is disturbed when it happens, but you may only notice the symptoms when you wake up in the morning.

The symptoms of nocturnal hypoglycaemia can include:

• headache, often likened to having a hangover
• feeling unusually tired in the morning
• damp sheets or clothing from sweating

Hypoglycaemia, or low blood sugar, mostly affects people who have diabetes. Now and then it happens for another reason, because of some other condition underneath.

Taking too much insulin for what your body needs at that moment is a common cause of hypoglycaemia (low blood sugar). Insulin is a medicine that helps control your blood glucose levels. Doctors commonly use it to treat type 1 diabetes, and it's also recommended for some people with type 2 diabetes.

Your blood glucose can also fall after you take too much of an oral hypoglycaemia medicine such as a sulphonylurea, which makes the body release insulin. This medicine is often used to lower blood glucose levels in people with type 2 diabetes.

If you have type 1 diabetes, keeping your blood glucose at the right level means balancing three things: how much insulin you inject, how much food you eat, and how much energy you burn during exercise.

Hypoglycaemia (low blood sugar) can happen when you've taken your usual dose of insulin, but the carbohydrate you've eaten is lower than normal or has been used up faster than usual. This can happen if you delay or miss a meal or snack, don't eat enough carbohydrate, or exercise more than you normally do.

People with diabetes can also get hypoglycaemia if they've drunk too much alcohol, or had alcohol on an empty stomach.

That said, it's not always possible to work out why a particular episode of hypoglycaemia has happened. Sometimes it comes on for no obvious reason.

Hypoglycaemia, or low blood sugar, is very rare in people who don't have diabetes, even in mild cases. The possible causes are outlined below.

People who don't have diabetes can still get hypoglycaemia. It can happen when the pancreas makes too much insulin after a large meal that is rich in carbohydrates. This is called reactive hypoglycaemia.

Nobody is sure why it happens, though it's thought to be more common in people who are overweight or have had gastric bypass surgery.

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

Hypoglycaemia can also happen in people who don't have diabetes. Other possible causes are:

• fasting or malnutrition, where you don't take in enough nutrients for your body to work properly
• binge drinking or heavy drinking of alcohol
• Addison's disease, a disorder of the adrenal glands (two small glands that sit on top of the kidneys)
• certain medicines, as 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

Most of the time, you can treat hypoglycaemia (low blood sugar) yourself once you recognise the symptoms.

The quickest way to treat hypoglycaemia is to have something sugary to eat or drink, about 15 to 20g of rapidly acting carbohydrate, so the attack ends. For example, you could have:

• a glass of fruit juice or non-diet soft drink
• between three and five dextrose tablets
• a handful of sweets

Avoid fatty foods and drinks at first, such as chocolate and milk. They don't usually contain as much sugar, and the sugar they do contain may be absorbed more slowly.

Once you've had something sugary, follow it with a longer-acting carbohydrate food, such as a few biscuits, a cereal bar, a piece of fruit or a sandwich.

A mild episode of hypoglycaemia usually takes around 15 minutes to pass. When you have a blood glucose meter, measure your blood sugar again after 15 to 20 minutes. Should it still be too low (below 4mmol), have some more sugary food or a drink and test your levels again in another 15 to 20 minutes.

Sometimes the person you're treating doesn't improve with the above. You may then be able to help by applying glucose gel to the inside of their cheeks and gently massaging the outside of their cheeks. Honey, treacle or jam will do if there's no glucose gel. It may take 10 to 15 minutes before they feel better. Don't do this if the person is drowsy or unconscious, because of the risk of choking.

You should contact your diabetes care team to find out the underlying cause if you have several episodes of hypoglycaemia a week. Your medication may need to be adjusted, or another condition causing the hypoglycaemia may need to be treated.

If someone loses consciousness because of severe hypoglycaemia (low blood sugar), put them into the recovery position and give them an injection of the hormone glucagon, if they have an injection kit. The injection raises their blood glucose level.

The injection should be given by a friend or family member who knows what they're doing, or by a trained health professional.

Dial 999 and ask for an ambulance if:

• a glucagon injection kit isn't available
• there's nobody around who's trained to give the injection
• the injection hasn't worked after 10 minutes

Never try to put food or drink into the mouth of someone who's unconscious, because they could choke.

If you're able to give a glucagon injection and the person wakes up, they should eat some longer-acting carbohydrate food, such as a few biscuits, a cereal bar or a sandwich.

Keep watching the person for any sign that the symptoms are coming back, in case they need to be treated again.

If you have diabetes, you can help prevent hypoglycaemia by sticking to your medicine plan and eating regular meals. Keep a check on your blood glucose levels too.

Checking your blood glucose regularly helps you keep it as normal and steady as you can. It also helps you spot the signs and symptoms of hypoglycaemia (low blood sugar) quickly.

Your blood glucose level can change through the day, so you may need to check it several times a day. How often depends on the treatment you're taking.

You can check it with a blood glucose meter. This is a small device that measures the concentration of glucose in your blood.

Read more about living with type 1 diabetes and living with type 2 diabetes.

If you have diabetes, hard physical activity can bring on hypoglycaemia (low blood sugar). Eating extra carbohydrate-based foods before and during exercise can help lower the chances of this happening.

If you take insulin, your doctor may advise you to cut your dose before you do strenuous physical activity.

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

Hypoglycaemia (low blood sugar) can come on suddenly, so you need to know its symptoms and be ready to treat it quickly. Tell your family and friends what signs to look out for, and let them know how to treat it too.

If you have diabetes, you are advised to carry some form of identification that states your condition. That way people can help you quickly and properly.

If you're at risk of hypoglycaemia (low blood sugar), carry sugary food and drink with you at all times. That way you can treat a mild episode as soon as it starts.

If you have diabetes, particularly type 1 diabetes, your doctor may suggest you also carry medicines such as glucose gel. You can use it to treat hypoglycaemia that doesn't respond to normal treatment.

If you're being treated with insulin, you'll usually be given a kit with an injection of a medicine called glucagon. Family members or your carer can be trained to give the injection, and it should be used if you lose consciousness because of severe hypoglycaemia.

You should try to avoid hypoglycaemia (low blood sugar) happening again and again during the night. This is called nocturnal hypoglycaemia, and it can dull the early warning symptoms you would normally get during a daytime episode.

If you do have nocturnal hypoglycaemia, you can 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 hypoglycaemia is most likely to occur

Hypoglycaemia can cause confusion, drowsiness or even unconsciousness, so it can put you and other road users at real risk when you drive.

If you have diabetes that needs treatment with insulin, you must:

• inform the DVLA and your insurance company
• test your blood sugar before driving, and at regular intervals while driving (at least every two hours)
• avoid driving if your blood glucose is low
• avoid driving for 45 minutes after treating hypoglycaemia
• carry rapid-acting carbohydrates with you in the vehicle at all times

If you have hypoglycaemia while driving, pull over and stop as soon as it's safe to do so. Take the keys out of the ignition and get out of the driver's seat before you treat it in the normal way.

If you have two or more episodes of hypoglycaemia that need assistance in a 12-month period, the law requires you to stop driving and inform the DVLA.

If you're a group two driver (you hold a licence to drive buses, coaches or lorries), the law requires you to stop driving group two vehicles immediately and inform the DVLA after a single episode of hypoglycaemia that needs assistance.

Tell your diabetes care team if you start having problems recognising hypoglycaemia, or if the episodes become more regular. Do this even if there were warning symptoms and you managed to treat them without assistance.

See the GOV.UK website for more information about hypoglycaemia and driving.