An abnormally low concentration of glucose in the blood. With regular meals, and despite an overnight fast, the level does not normally drop at any time below its range of 3.5-5.5 mmol/litre. Healthy people become hypoglycaemic only after a more prolonged fast, or heavy exercise without adequate intake. Severe hypoglycaemia can occur in people with diabetes whose insulin dosage has been excessive relative to food intake. Because the brain depends exclusively on glucose for its metabolism, they may lose consciousness in hypoglycaemic coma, but wake up rapidly if glucose is infused into a vein.

— Stuart Judge

See blood sugar; insulin.

The Oxford Companion to the Body. Copyright © 2001, 2003 by Oxford University Press. All rights reserved.