Hypoglycemia occurs when the level of glucose (sugar) in the blood is too low. Normally, your body keeps your blood glucose within a concentration range of about 70 mg/dL to 140 mg/dL (4.0 mmol/L to 8.0 mmol/L). In order to do this, the body has mechanisms that involve the hormone insulin, which is made by the pancreas, as well as several other hormones.
Insulin lowers the amount of glucose in your blood by signaling the cells in the body to take up glucose as fuel. When blood sugar levels rise, the pancreas responds by releasing insulin to promote glucose transfer from the bloodstream to the cells.
Your body uses glucose as its main fuel. The brain requires a constant supply of blood glucose and will signal the adrenal glands to release two hormones called adrenaline and cortisol whenever blood glucose levels are low. The adrenaline and cortisol then signal the liver to convert the carbohydrates it stores (from the foods we eat) into glucose and release it into the bloodstream.
The pancreas is also involved in raising blood glucose levels if they fall too low. When blood sugar is low, the pancreas releases the hormone glucagon, which increases blood sugar by signaling the liver to convert stored carbohydrates into glucose and to create new glucose molecules from other substances (such as amino acids) in the liver. If these mechanisms don't work properly, the blood glucose remains too low and the brain won't be able to function normally.
Hypoglycemia can be caused by medications. Medication-related hypoglycemia occurs most commonly in people who have diabetes, especially type 1 diabetes (a type of diabetes where the pancreas does not make insulin). In both type 1 and type 2 diabetes it can occur when someone is given too much insulin or other medications for diabetes that promote the release of insulin from the pancreas in relation to their current level of exercise and diet. This can drastically lower blood sugar, resulting in hypoglycemia. There are also other medications that can cause hypoglycemia in people with diabetes and people that do not have diabetes, such as certain medications for high blood pressure (e.g., atenolol*, metoprolol, propranolol), certain antidepressants (e.g., phenelzine, tranylcypromine), quinine, haloperidol, and trimethoprim - sulfamethoxazole.
Other types of hypoglycemia include fasting hypoglycemia and reactive hypoglycemia. In fasting hypoglycemia, a person gets low blood sugar if they haven't eaten for a while. Reactive hypoglycemia is low blood sugar that occurs after eating, usually due to eating a meal high in carbohydrates. This causes the blood sugar to rise rapidly, which in some cases may stimulate excess secretion of insulin. People may also have reactive hypoglycemia if they have trouble digesting fructose and galactose (two types of sugars found in foods), or leucine (an amino acid found in foods). It may also occur after some types of stomach surgery, as this may cause sugars to be absorbed too quickly, leading to excessively high insulin levels, which can cause hypoglycemia.
Hypoglycemia can also be caused by a problem with the pituitary or adrenal glands, pancreas, kidneys, or liver. The pituitary gland controls the body's production of some of the hormones needed to raise the body's blood sugar levels if they fall too low. These hormones include cortisol, which is released from the adrenal glands; glucagon, which is released from the pancreas; and adrenaline, which is released from the adrenal gland medulla. These hormones all help raise blood sugar levels. If they are not working properly, this could cause hypoglycemia.
Hypoglycemia can also result when the liver can't properly store carbohydrates or convert them into glucose. A tumor on the pancreas can also cause hypoglycemia by causing too much insulin to be released.
People who drink alcohol excessively (without eating) can develop severe hypoglycemia. In cases of severe kidney dysfunction, hypoglycemia might also develop.