Hypoglycaemia - Low Blood Glucose level

Hypoglycaemia - a low blood glucose level - is a recurrent problem for many people with diabetes, and it is frequently cited as being the main barrier to achieving good blood glucose control in those people on insulin.

What's covered on this page

What is Hypoglycaemia?

Short Term Effects of Hypoglycaemia

Treating Hypoglycaemia

Nocturnal Hypoglycaemia

Long Term Effects of Hypoglycaemia

Normal Glucose Regulation and 'Counterregulation'

What is Hypoglycaemia?

Hypoglycaemia in people with diabetes is a low blood glucose level, causing a number of unpleasant effects ranging from shaking, sweating and a racing heart beat, through to behavioural changes, seizure and coma.



less than 4.0 mmol/L

Tell people that you have diabetes
- it could save your life!

Carry Diabetic ID at all times...
Consider joining the MedicAlert program.



Who suffers from hypoglycaemia?

All people with any type of diabetes can potentially suffer mild forms of hypoglycaemia, including symptoms related to a rapidly falling or lower than normal* blood glucose level. However, significant hypoglycaemia is usually only suffered by those people taking insulin, or drugs that increase insulin production/ action, for the management of blood glucose.

* Some symptoms of hypoglycaemia can be felt at a normal or even high-normal blood glucose level if you have been running high for a significant period of time. Equally, a rapidly falling blood glucose level can elicit symptoms of hypoglycaemia before levels drop below 4 mmol/L.


Why does hypoglycaemia occur in people with diabetes?

Diabetes is generally associated with a high blood glucose level. However, when treated with insulin, or tablets that increase natural insulin activity, diabetes becomes a delicate balancing act, and, because of the multitude of factors that affect blood glucose levels, total normalisation of blood glucose is just not possible.

There are a whole host of factors that affect blood glucose levels and if these are not precisely balanced with insulin reaching the bloodstream (either from the pancreas, or from the injection site) on an hour-by-hour, minute-by-minute basis, then the blood glucose level may fall outside the normal range. If it drops too low, hypoglycaemia results. People with diabetes frequently refer to this experience as "having a hypo" or "going hypo".


Lowers blood glucose
Raises blood glucose


Sulphonylurea or meglitinide tablets (see "Tablets for Type 2's")



*Massage, exercise, or a warm bath may increase insulin absorption from the injection site and cause a rapid lowering of blood glucose

Food - especially carbohydrates

Emotional stress

Illness, any infection


Some medications

Dawn effect (a rising blood glucose early in the morning)

Variable effect on blood glucose level

Monthly periods in women

Some types of stress


Common causes of hypos in people with diabetes therefore include the following:

  • Too much insulin
  • Too high a dose of diabetes tablets
  • Lack of food (carbohydrates)
  • Exercise
  • Alcohol


Can hypoglycaemia cause death?

It is rare, but yes - hypoglycaemia can cause death. Some reports suggest that as many as 2-4 % of deaths of people with Type 1 diabetes may have been attributed to hypoglycaemia (1, 2). Deaths related to hypoglcaemia induced by certain sulphonylurea tablets have also been reported (3, 4)


Short Term Effects of Hypoglycaemia

Glucose is the preferred fuel for the brain. However, the brain cannot make glucose, and can only store a few minutes' supply in the form of glycogen - so it is entirely dependent on a continuous supply of glucose via the bloodstream. When the level of glucose in the blood falls below a certain level, the brain - the body's control centre - starts to malfunction.

Signs and symptoms

Signs of hypoglycaemia are recognisable clinical changes in an individual that are either visible or measured. Symptoms of hypoglycaemia are descriptive terms for what the person experiences. Signs and symptoms are caused by the direct and indirect effects that low blood glucose levels have on the nervous system.

The table below shows how symptoms are classified by the medical profession. As a person with diabetes, your main objective is to recognise the symptoms early on, do a blood glucose test to verify that your blood glucose is low, then take appropriate action as quickly as possible.


Neurological responses Physiological responses
Result of the perception of physiological changes caused bythe activation of the autonomic nervous system triggered by hypoglycaemia Result of direct effects of low blood glucose on the brain - limits neuronal metabolism - i.e. the nerves are starved of glucose

"Autonomic" or "NEUROGENIC" symptoms

  • Sweating
  • Shakiness
  • Palpitations
  • Hunger, or a compulsion to eat


  • Confusion
  • Drowsiness
  • Uncharacteristic behaviour
  • Difficulty with speech
  • Loss of coordination

In addition, some symptoms come under the rather vague heading of "GENERAL MALAISE" - these include:

  • Headache
  • Nausea



Hypoglycaemia awareness

Recognising the signs and symptoms of diabetes is "hypoglycaemia awareness". If you realise that your blood glucose level is starting to fall and you take action to correct it (i.e. - have some glucose, see below) then, apart from some inconvenience, all should be well.

However if you fail to realise that your blood glucose level is dropping until it gets too a very low level, then we call this a loss of hypoglycaemia awareness. This may make you susceptible to severe hypoglycaemia, which can be dangerous and is potentially life-threatening.

If you are unable to detect mild hypoglycaemia from symptoms alone, you should:

  • Increase the number of times you test your blood glucose each day
  • Consider snacking more often or eating more regular meals
  • Always test your blood glucose level before driving or using potentially dangerous equipment
  • Discuss the situation with your diabetes healthcare team
  • Educate your friends, relatives, and co-workers about hypoglycaemia so that they can recognise the condition
  • Keep a glucagon injection kit to hand (see 'severe hypoglycaemia' below)


Treating Hypoglycaemia

Quick Fix Solution

The treatment for a low blood glucose level is simple - Glucose! You can use glucose powder or tablets. (Don't be confused by the term 'dextrose' - it's the same thing as glucose.) 10 or 15g of glucose should be taken immediately. Then wait 5 minutes before having some other form of carbohydrate - biscuits, or a muesli bar, for example.

It's a good idea to keep some blood glucose boosters with you at all times. Glucose tablets, jelly beans, and hard candies are compact, portable, and last a long time in desks, purses, lockers, and glove compartments.

Depending on what caused the hypoglycaemia and when you will eat your next meal, you may need to have an extra starchy snack - a sandwich or cereal bar, for example - to keep you going.

If a person is unable (or unwilling) to treat the hypoglycaemia themselves, then help may be needed in the form of a glucagon injection. Glucagon is a natural hormone, which raises the blood glucose level by encouraging the liver to release glucose into the bloodstream. It can be injected by a friend or family member, or, in the worst-case scenario, by a paramedic.


"Prevention is Better Than Cure"

In order to prevent hypoglycaemia whenever possible, it is necessary to understand why it happens and when it is most likely to happen. Then you should be able to take appropriate action to keep your blood glucose level above 4 mmol/l.

Hypoglycaemia has many causes:

  • Too much insulin or diabetes medication - these treatments stimulate the cells to remove too much glucose from the blood.
  • Too little food, particularly carbohydrates - if you don't eat regularly, you may not consume enough food to keep blood glucose levels within the normal range. Delayed or missed meals are the most common cause of hypoglycaemia.
  • Too much exercise - exercise uses up blood glucose.
  • Drinking alcohol - alcohol lowers blood glucose levels. Usually, as blood glucose levels fall, the liver releases stored glucose into the bloodstream. But alcohol interferes with this process. It is particularly dangerous for people with diabetes to drink on an empty stomach. Blood glucose levels can fall so fast so quickly that you may lose consciousness quite suddenly.
  • Pregnancy - pregnancy often makes women less aware of hypoglycaemia. Pregnancy also involves eating for two, which may require substantial changes in food intake and insulin doses.

Hypoglycaemia is most likely to occur:

  • Just before meals, when blood glucose is naturally low
  • During or after strenuous exercise
  • When insulin is peaking
  • When you suspend your usual daily routines, particularly if your alcohol intake increases while your food intake falls
  • At night, particularly if you've been more active the day before, eaten less or consumed alcohol during the evening

Regular testing of your blood glucose level
is key to understanding and preventing hypos.


Severe hypoglycaemia

Severe hypoglycaemia is usually defined as that 'requiring assistance from another person'. It is usually necessary to trest severe hypoglycaemia with glucagon (see "Treating Hypos" above).


Nocturnal Hypoglycaemia

Nighttime hypoglycaemia can be a problem for some people if they do not wake up. Common signs include damp sheets and pyjamas, nightmares, crying out in sleep, or feeling tired, irritable or confused on waking. A high early morning blood glucose level sometimes indicates hypoglycaemia during the night - the liver is stimulated to release glucose and 'overcompensates'.

To minimise risk of nighttime hypoglycaemia, test your blood glucose level periodically between 2 and 3 a.m. Determine how your level relates to your food, exercise, and insulin or medication the previous day and adjust them accordingly.

* Fits are quite common in young children, especially if hypoglycaemia occurs during the night. Don't worry - this is not epilepsy and generally causes no serious damage. As children grow older the fits become less frequent and most children grow out of them altogether.


Longer Term Effects of Hypoglycaemia

In the long term, hypoglycaemia may repeatedly reduce or interefere with physical and mental functioning, with the potential to significantly affect social functioning.

Psychologically, hypoglycaemia - particularly severe hypoglycaemia - can have devastating effects in the long run.


Fear of Hypoglycaemia

Hypoglycaemia can be an unpleasant experience, and as a result some people suffer anxiety or fear of hypoglycaemia (FoH). This is a clinically recognised condition (8) and may be quite widespread amongst people with diabetes. Some people may go to extreme lengths in order to avoid having hypoglycaemia (e.g. missed or reduced insulin injections). Poor metabolic control and emotional/psychological problems inevitably result from (FoH).

Recognising and accepting the prolem is the first step in overcoming FoH. Blood glucose awareness training and cognitive behavioural therapy can help to improve the situation. Support from family and friends helps too.


Loss of hypoglycaemia awareness

As a rule, warning signs of a hypo are experienced as the blood glucose level starts to drop. These might include sweating, shaking or hunger. It has been noted in many cases that gradually, over a period of years, these warning signs start to come on later. This means that the blood glucose may fall very low before the individual becomes aware of the situation and realises that he/she needs to take glucose. People with hypoglycaemia unawareness may suffer from repeated severe hypos, and may be at risk of fitting or unconsciousness.

It's a vicous circle!

Hypoglycaemia itself can have the effect of reducing hypoglycaemia awareness - in effect this means that once you've had a hypo, you're more likely to have another one.

To get out of the vicous circle blood glucose levels may need to be kept slightly higher than you would otherwise aim for - in order to avoid hypoglycaemia. After a few days warning signs should return to normal.

 Factors relating to loss of hypo awareness are considered in more depth in the section below 'Normal Glucose Regulation and Counterregulation'


Changes in brain function

Recently another long term problem associated with hypoglycaemia has come to light. Some people who have had Type 1 diabetes for many years seem to have suffered from damage to the frontal lobes in the brain and this is thought to be related to frequent or severe episodes of hypoglycaemia over time. As a result, these people appear to suffer from lack of concentration, poor judgment, a loss of reasoning and a reduced ability to interact with other people.

Many such people also have signs of the more well-defined complications outlined above; it is possible that nerve damage in particular, might add to the problem.

Recurrent severe hypoglycaemia in young children has also been reported to affect learning and development to some extent in certain individuals. However, on a positive note, a recent study carried out in Australia (5) suggested that "seizures/coma at a young age does not necessarily result in gross cognitive or behavioral impairment."

Finally, although severe prolonged hypoglycaemia can potentially cause some degree of permanent brain damage, it is rare - complete recovery is the general rule (6).


Normal Glucose Regulation and 'Counterregulation'

How does the body normally respond to a falling blood glucose level in people who do NOT have diabetes?

People who do not have diabetes rarely encounter significant hypoglycaemia, even after prolonged fasting. This is because the body has an excellent defence mechanism - called counterregulation - which is triggered as the blood glucose level falls below a certain threshold.

So, normally, as the blood glucose level reaches this glycaemic threshold (see box), the automatic production of the hormones glucagon and epinephrine (adrenalin), act to raise the blood glucsoe and a normal blood glucose level is quickly restored.



Counterregulation activated in people who do NOT have diabetes

3.8 mmol/L

(healthy young adult)

Onset of symptomatic responses 3.0 mmol/L
Onset of brain ('cognitive') dysfunction 2.8 mmol/L


Counterregulation in people who do NOT have diabetes prevents the blood glucose from falling to levels low enough to cause symptoms. (Counterregulatory responses in people who DO have diabetes are actually responsible for a number of the symptoms experienced.)


'Counterregulation' in diabetes

In peole with diabetes, the counterregulatory response is impaired, particularly in those poeple with Type 1 diabetes. Research suggests that after about 5 years of being diagnosed with Type 1 diabetes, most people will have a defective glucagon response to hypoglycaemia. This means that the liver does not top up the falling blood glucose level as it should normally do. Further, with repeated episodes of hypoglycaemia, the epinephrine response can become blunted and this is associated with loss of hypoglycaemic awareness, i.e. loss of warning signs. Interestingly, reports suggest that this effect may be greater in men than in women.

Counterregulatory responses in people who have diabetes are related to a number of the symptoms experienced. Blunting of these responses in diabetes reduces the level of blood glucose at which symptoms are experienced and this is associated with the development of 'hypoglycaemia unawareness'.

Hypoglycemia-associated autonomic failure (HAAF) is a functional disorder distinct from classic diabetic autonomic neuropathy. It is a dynamic phenomenon that can be induced (by prior hypoglycemia) and reversed (by avoidance of hypoglycemia) and is manifested clinically by recurrent iatrogenic hypoglycemia.

The combination of reduced counterregulatory mechanisms and hypoglycaemia unawareness significantly increases the risk of severe hypoglycaemia.


Differences between men and women

Women have been shown to have significant reductions in the critical counterregulatory hormones, glucagon and epinephrine, together with blunted rates of endogenous glucose production, compared to men. When fasting, women's blood glucose levels fall lower than men. So why is it that women with Type 1diabetes don't suffer hypoglycaemia more often than men? The DCCT data have shown that , if anything, women have a reduced risk of severe hypoglycemia during intensive therapy compared to men. Researchers in Tennessee (7) suggest that:
1) antecedent hypoglycemia produces less blunting of counterregulatory responses to subsequent hypoglycemia in women relative to men;
2) two episodes of antecedent hypoglycemia can overcome the greater SNS response to hypoglycemia usually found in men; and
3) the reduced susceptibility of women to the blunting effects of antecedent hypoglycemia may be the mechanism explaining why, despite inherently reduced SNS counterregulatory responses, female type 1 DM patients have a similar prevalence of hypoglycemia compared to men.



1. Cryer PE. Hypoglycemia. Pathophysiology, Diagnosis and Treatment. New York, Oxford University Press, 1997. (Buy from Amazon)

2. Laing SP, Swerdlow AJ, Slater SD, Botha JL, Burden AC, Waugh NR, Smith AW, Hill RD, Bingley PJ, Patterson CC, Qiao Z, Keen H. Diabet Med. 1999 Jun;16(6):466-71.The British Diabetic Association Cohort Study, II: cause-specific mortality in patients with insulin-treated diabetes mellitus. (PubMed)

3. Campbell IW. Hypoglycaemia and type 2 diabetes: sulphonylureas. In 'Hypoglycaemia and Diabetes:Clinical and Physiological Aspects'. Frier B, Fisher BM Eds. London, Edward Arnold, 1993; p387-92. (Buy from Amazon)

4. Gerich JE. Oral hypoglycemic agents. N Engl J Med. 1989 Nov 2;321(18):1231-45 [Erratum in:N Engl J Med 1990 Jan 4;322(1):71] (PubMed)

5. Strudwick SK, Carne C, Gardiner J, Foster JK, Davis EA, Jones TW. Cognitive functioning in children with early onset type 1 diabetes and severe hypoglycemia. J Pediatr. 2005 Nov;147(5):680-5. (PubMed)

6. Cryer PE, Davis SN, Shamoon H. Hypoglycemia in diabetes. Diabetes Care. 2003 Jun;26(6):1902-12. (PubMed)

7. Davis SN, Shavers C, Costa F. Gender-related differences in counterregulatory responses to antecedent hypoglycemia in normal humans. J Clin Endocrinol Metab. 2000 Jun;85(6):2148-57.