Editorials

Severe hypoglycaemia and cognitive impairment in diabetes

BMJ 1996; 313 doi: http://dx.doi.org/10.1136/bmj.313.7060.767 (Published 28 September 1996) Cite this as: BMJ 1996;313:767
  1. Ian J Deary, Professor of differential psychology,
  2. Brian M Frier, Consultant physician
  1. Department of Psychology, University of Edinburgh, Edinburgh EH8 9JZ
  2. Department of Diabetes, Royal Infirmary of Edinburgh, Edinburgh EH3 9YW

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    Two events within the past year have highlighted the question of the possible lasting cerebral effects of repeated severe hypoglycaemia in people with insulin dependent diabetes mellitus. Firstly, in August 1995, the British Diabetic Association specifically requested research proposals on the cognitive effects of diabetes after their working party on cognitive impairment identified repeated severe hypoglycaemia as one possible cause of (mostly) mild cognitive decrements in some people with insulin dependent diabetes mellitus (unpublished data). Secondly, the diabetes control and complications trial has reported no untoward neuropsychological effects of severe hypoglycaemia in patients with insulin dependent diabetes.1

    The human brain accounts for about 20% of the body's metabolic consumption and is obliged to use glucose exclusively as its fuel. Therefore, when it is temporarily starved of glucose, brain functions suffer: thinking processes are impaired and a tense, tired mood state ensues. If profound neuroglycopenia continues untreated the result may be coma, seizure, and (rarely) severe brain damage. Hypoglycaemia is associated with significant morbidity and accounts for about 1-2% of deaths among diabetic patients,2 although this is still much lower than the mortality from diabetic ketoacidosis (6%). The severity of hypoglycaemia is defined by individuals' ability to treat themselves: severe episodes are those that require help from a third party to effect recovery. For people with insulin dependent diabetes, hypoglycaemia is the most feared side effect of treatment. Because episodes of severe hypoglycaemia can involve relatively prolonged neuroglycopenia, concern has arisen about their long term effects on brain function. …

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