What is hypoglycaemia?

Hypoglycaemia means low blood sugar.


Mainly two hormones, insulin and glucagon, control the blood glucose level. Cortisol, growth hormone, adrenaline and noradrenaline also influence blood sugar levels. When the blood sugar level is high, the pancreas secretes insulin. When the blood sugar level is low, the liver releases glycogen in order to bring the blood sugar level back to normal.

The normal range for blood sugar is approximately 3.5 millimol per litre (mmol/l) to 6.5 mmol/l, depending on when the person last had a meal. Blood sugar can sometimes fall below 3.5 mmol/l to as low as 2.9 mmol/l without this being an indication of a serious disease. However, blood sugar levels below 2.5 mmol/l nearly always indicate a serious abnormality. Symptoms of hypoglycaemia occur at different blood glucose levels in different people.

Glucose is a form of sugar and the body's main fuel. Low blood sugar (hypoglycaemia) occurs when the levels of glucose in the blood drop too low to provide fuel for the body's activities. The term 'blood sugar' is derived from the fact that glucose is absorbed into the bloodstream during digestion. The body's main dietary sources of glucose are carbohydrates (sugars and starches).


A complication of diabetes is the most common cause of hypoglycaemia, namely when a diabetic takes too much oral medication, too much insulin, misses or delays meals, miscalculates the amount of food needed for the amount of insulin administered, takes too much exercise or drinks alcohol.

Other causes include:

  • Drug-induced hypoglycaemia
  • Intentional overdose of insulin or other medicine used to lower blood glucose – alcohol and quinine (used in some antimalarial drugs) can lead to hypoglycaemia. 
  • Pre-diabetes
  • Liver disease
  • Surgical removal of the stomach
  • Tumours that release too much insulin (insulinoma)
  • High fevers

Rare causes include:

Fasting hypoglycaemia:

  • Occurs when the stomach is empty, usually in the early morning upon awakening. Symptoms are the same as for other forms of hypoglycaemia, but may include lack of concentration. Hereditary enzyme or hormone deficiencies, liver disease and tumours that produce insulin can cause fasting hypoglycaemia. 

Reactive hypoglycaemia:

  • This form of hypoglycaemia, which occurs after a meal, is common in patients whose stomach has been surgically removed. Glucose is rapidly absorbed into the bloodstream, resulting in hyperglycaemia or high blood glucose. In order to correct the hyperglycaemia, the pancreas releases too much insulin, pushing blood sugar down and causing hypoglycaemia.

Reactive hypoglycaemia sometimes occurs in patients who have not had their stomach removed surgically and do not have a family history of diabetes. These patients have symptoms that are usually associated with hypoglycaemia. They are classified as having reactive hypoglycaemia of unknown cause.


Acute onset of:

  • Weakness
  • Drowsiness
  • Hunger
  • Confusion
  • Nervousness
  • Dizziness
  • Trembling
  • Rapid heartbeat
  • Heavy or cold perspiration
  • Pale or ashen skin
  • Tingling in hands and feet

The symptoms are caused by the adrenaline that the adrenal glands release when hypoglycaemia occurs, to restore and maintain glucose levels in the blood. The adrenaline does this by mobilising stored glycogen and fat and converting them into glucose. Glucose is the brain's main source of energy. As hypoglycaemia starves the brain of the energy derived from glucose, symptoms may range from headache and mild confusion to loss of consciousness, seizure and coma. Severe hypoglycaemia can cause permanent brain damage or death.


Hypoglycaemia in non-diabetics is very rare but can occur under certain conditions such as early pregnancy, prolonged fasting and long periods of strenuous exercise. Hypoglycaemia is common in alcoholics and binge drinkers.

When to see a doctor?

If you have frequent attacks of low blood sugar, it is best to consult a health professional for advice on how to keep your blood sugar levels under control, and to have your overall health evaluated to determine the underlying cause of this condition. If you are diabetic and lose consciousness during an attack of hypoglycaemia, you need immediate medical treatment. If you are a diabetic and you have symptoms of hyperglycaemia several times within a few days, contact your doctor.


The symptoms of hypoglycaemia are often vague and not very specific, which can make diagnosis a problem. The vagueness of symptoms may also lead to confusion between hypoglycaemia and other conditions. Three criteria, known as Whipple's triad, must be met to establish hypoglycaemia as the cause of a patient's symptoms:

  • The patient has (or complains of) symptoms of hypoglycaemia.
  • Blood glucose levels, measured while the person is suffering from those symptoms, are found to be 2.5 mmol/l or less (female patients) or 2.7 mmol/l or less (male patients).
  • The symptoms are quickly relieved when sugar is taken.

To find out if diabetes is the cause of several attacks of hypoglycaemia, a doctor can do a glucose tolerance test (this test measures the body's ability to process glucose) or a blood test two hours after a meal. Home test kits to measure blood glucose quickly are available for use by diabetics so that they can monitor and regulate their blood glucose levels at home.

In cases where insulin-producing tumours are the cause of hypoglycaemia, the tumours can be localised with radiological tests. The amount of insulin, glucose and proinsulin can be measured during a 12-hour fast and the tumours can be diagnosed using this method.


The first step in treating hypoglycaemia is to identify the underlying cause of the condition. Immediate treatment consists of administering large amounts of glucose, repeating the treatment in the case of persisting symptoms. Severe hypoglycaemia must be treated without delay. If left untreated, hypoglycaemia will soon cause neurological deterioration.


Nutrition and diet should be part of the treatment of hypoglycaemia. This also applies to patients who have been diagnosed with reactive hypoglycaemia that is not related to other medical conditions or problems. 

Foods that boost blood sugar include whole grains, cheese, lean meat and fish, all eaten as small, frequent meals. A drink of fruit juice may be beneficial during an attack of low blood sugar.

Supplements of chromium, a mineral found in foodstuffs such as brewer's yeast, molasses and wholewheat bread and cereal, can help to improve blood sugar levels.

Alcohol, caffeine and smoking are best avoided, as they are known to cause large swings in blood sugar levels. 


A diabetic who loses consciousness during an attack of hypoglycaemia needs immediate medical treatment in the form of a glucose injection administered directly into the bloodstream (by a paramedic, nurse or doctor). This can save the diabetic's life.


In cases where insulin-producing tumours are the cause of hypoglycaemia, the tumours can be localised with radiological tests and removed by a surgeon.

Disclaimer: The information provided in this article was correct at the time of publishing. At Mediclinic we endeavour to provide our patients and readers with accurate and reliable information, which is why we continually review and update our content. However, due to the dynamic nature of clinical information and medicine, some information may from time to time become outdated prior to revision.