Reduced awareness of hypoglycaemia in the elderly despite an intact counter-regulatory response

We investigated awareness of hypoglycaemia and its counter-regulatory hormone response in six young (ages 24-49, mean 30 years) and seven elderly (ages 65-80, mean 72 years) healthy non-diabetic subjects. A hyperinsulinaemic glucose clamp was used to control blood glucose level on two separate occasions. During the hypoglycaemic study, blood glucose was lowered in a stepwise manner to plateaus of 3.5, 3.0 and 2.5 mmol/l. A symptom score, visual reaction time test and digit symbol substitution test was completed pre-study, and at the end of each plateau. Pulse rate, blood pressure and counter-regulatory hormone measurements were taken every 15-30 min. The euglycaemic study was identical except that blood glucose remained at the fasting level. During hypoglycaemia, the elderly group had lower symptom scores than the young group (total relative score at glucose 2.5 mmol/l, mean +/- SEM: elderly -1 +/- 2.5, young 23 +/- 6.7, p < 0.01) and fewer individual symptoms despite a similar counter-regulatory hormone response. There was no difference in deterioration of the visual reaction times or digit symbol substitution scores during hypoglycaemia between the age groups. Unlike the young group, the elderly subjects had no tachycardia in response to hypoglycaemia. Their reduced awareness of hypoglycaemia may be due to an impaired end-organ response to counter-regulatory hormones, resulting in fewer symptoms.