hypoglycemia

If hyperglycemia is a flooded river, hypoglycemia is the river running dry. The brain runs almost entirely on glucose and has no large store of its own, so when blood sugar falls too low the brain is the first to suffer — bringing on shakiness, sweating, confusion, and, if not corrected, seizures or loss of consciousness.

Hypoglycemia is an abnormally low blood glucose, generally below about 3.9 mmol/L (70 mg/dL), at which the body mounts a defensive response. As glucose falls, the pancreas first switches off insulin, then counter-regulatory hormones — glucagon, then epinephrine, cortisol, and growth hormone — act to raise it again by releasing stored glucose and making new glucose. Early ‘adrenergic’ warning symptoms (tremor, palpitations, hunger, sweating) precede the ‘neuroglycopenic’ symptoms of an under-fueled brain.

In people with diabetes, hypoglycemia is most often an iatrogenic side effect — caused by too much insulin or by sulfonylureas, by missed meals, or by exercise. Repeated episodes can blunt the warning symptoms, a dangerous condition called hypoglycemia unawareness. Outside diabetes, true hypoglycemia is uncommon and warrants a search for causes such as insulin-secreting tumors, certain drugs, or adrenal insufficiency.