Hypoglycemia

Hypoglycaemia means blood glucose low enough to impair function, conventionally below 3.9 mmol/L. The distinction that matters most is who has it. In people taking insulin or sulfonylureas, hypoglycaemia is common, dangerous and the main limiting factor in diabetes treatment — severe episodes cause confusion, seizures and loss of consciousness, and repeated mild episodes blunt the warning symptoms in a phenomenon called hypoglycaemia unawareness. In people not on diabetes medication, true hypoglycaemia is uncommon. The frequent complaint of shakiness and irritability a few hours after eating is usually reactive or postprandial hypoglycaemia, where an exaggerated insulin response to a high-glycaemic meal overshoots — real, uncomfortable, but rarely dangerous and highly responsive to changing meal composition. Genuine fasting hypoglycaemia in a non-diabetic adult is a red flag requiring investigation for insulinoma, adrenal insufficiency, liver disease or medication effects. The classic Whipple triad — symptoms, a documented low glucose, and relief on correction — is what distinguishes real hypoglycaemia from the many conditions that mimic it, which is why measuring glucose during an episode is the single most useful step.

• •Shakiness, trembling and sweating
• •Palpitations and anxiety from the adrenaline response
• •Intense hunger
• •Irritability and sudden mood change
• •Difficulty concentrating, confusion and slurred speech
• •Blurred vision and dizziness
• •Tingling around the lips
• •Seizures or loss of consciousness in severe episodes
• •Nightmares and waking sweaty in nocturnal hypoglycaemia
• •Loss of warning symptoms over time — hypoglycaemia unawareness

• •Insulin or sulfonylurea treatment for diabetes — by far the most common cause
• •Missed or delayed meals while on glucose-lowering medication
• •Unplanned exercise without adjusting medication or carbohydrate
• •Alcohol, which blocks the liver's glucose production, especially overnight
• •Reactive hypoglycaemia after high-glycaemic meals
• •Post-bariatric surgery hypoglycaemia from rapid gastric emptying
• •Adrenal insufficiency and pituitary disease
• •Severe liver or kidney disease
• •Insulinoma — a rare insulin-secreting tumour
• •Certain medications including quinine and high-dose salicylates

Glucose falls when insulin action exceeds glucose supply. In treated diabetes this follows a mismatch between medication dose, carbohydrate intake and activity. In reactive hypoglycaemia, a rapidly absorbed carbohydrate load provokes a large insulin surge that peaks after glucose absorption has finished, driving levels below baseline. The body defends itself by suppressing insulin and releasing glucagon and adrenaline — the adrenaline surge produces the shakiness, sweating and palpitations, while low glucose supply to the brain produces the confusion and slurred speech that come later.