Diabetes mellitus and the rate of cognitive ageing

Objectives. There is some evidence that besides affecting peripheral neural function diabetes may also cause more widespread changes in the central nervous system which reduce cognitive efficiency and so, also, independence and quality of life. The present study explores whether diabetes mellitus is a compounding factor in average declines in cognitive performance observed in old age. Design. A sample of diabetics and controls were compared on a battery of cognitive tasks previously used in cognitive ageing research. Methods. Thirty-three insulin dependent (IDDM), 135 non-insulin dependent (NIDDM) diabetics and 2191 non-diabetics aged between 50 and 91 years were compared on two tests of general intellectual ability, and on three tests of verbal memory. Results. Overall, the combined IDDM and NIDDM groups had significantly lower average scores than the controls group on all cognitive tasks. Detailed analyses revealed most cognitive impairment for the NIDDM sub-group whose condition was managed by hypoglycaemic drugs, slightly less for those managed by diet, and no impairment for the IDDM group. These effects were independent of age, depression, socio-economic status, and presence of other illnesses. Conclusions. Together with other recent studies these data emphasize the need for early detection and effective management of diabetes in older patients.