By Dr Ananya Mandal, MD
Hypoglycemia or low blood sugar is a problem that arises in the management of diabetes. Diabetes mellitus usually describes a persistently high blood sugar. However, various factors can cause blood sugar to plummet such as taking too much antidiabetic medication, engaging in vigorous exercise which can deplete the body of sugar, drinking too much alcohol or missing meals or snacks.
However, the majority of diabetic patients experience symptoms that indicate when their blood sugar is becoming too low. Most diabetics learn to recognize and act upon such warning signs, examples of which include:
Anxiety and feeling of dread
In some people, these symptoms do not necessarily manifest and the diabetic individual may not recognise that their blood sugar has fallen too low. This is called hypoglycemia unawareness. Individuals with long-standing insulin-dependent (type 1) diabetes are at the greatest risk of hypoglycemia unawareness but type 2 diabetics who are taking insulin due to advanced disease are also at risk.
In healthy individuals or type 2 diabetics with less advanced disease, a fall in blood sugar gives rise to the release of glucagon and epinephrine which stimulate the liver to convert glycogen to glucose and release this into the blood to normalize glucose levels. In addition, epinephrine secretion causes the physical symptoms such as palpitations and tremors that can alert a person to their low blood sugar level.
In diabetic patients who are reliant on insulin, a fall in blood glucose is not accompanied by a fall in insulin nor does it trigger the usual counter-regulatory systems such as glucagon and epinephrine secretion. In the absence of the release of these hormones, blood sugar levels are not normalized and the patient is not alerted to the fact that the sugar levels are low. Hypoglycemia unawareness in these patients can also arise due to diabetic neuropathy blunting the effects mediated by the autonomic nervous system in response to hypoglycemia.
The brain may also be desensitized to the symptoms of hypoglycaemia as it becomes "used to" low blood sugar levels. With repeated hypoglycemia, the brain increases the number of glucose transporters in neurons to enable the brain to receive a constant supply of glucose, even when blood sugar levels are low. This lowers the hypoglycemic threshold at which epinephrine is released, therefore increasing the likelihood of hypoglycemia unawareness.
In addition, certain medications may mask the symptoms of hypoglycemia. For example, certain blood pressure medications such as beta blockers may blunt the effects of epinephrine so that the typical warning signs are not experienced.
Reviewed by Sally Robertson, BSc
Last Updated: Nov 3, 2013