Effect of the treatment of Type II diabetes mellitus on the development of cognitive impairment and dementia

There is increasing interest in preventing cognitive impairment and dementia in later life. Epidemiological evidence shows a relationship between cognitive impairment and Type II diabetes. This association is stronger in patients who have been diagnosed for longer periods of time and in those who are on insulin therapy. There is little information on the short- and long-term influence of type of treatment and level of metabolic control on cognitive function of people with diabetes. To assess the effects of different types and intensities of treatments for Type II diabetes on cognitive function. The Cochrane Control Trials Register, MEDLINE, EMBASE, PsycINFO, SIGLE LILACS and CINAHL as well as a number of ongoing trials databases were searched on 11 June 2002 using appropriate strategies. Randomized controlled trials in which different treatments for Type II diabetes have been compared and in which measures of cognitive function were made at entry and after the treatment. Two reviewers independently assessed trial quality. Five trials were identified for possible inclusion but none of them could be included. In one, cognitive function was assessed before and after intensive or conventional diabetic treatment, but the comparison was not double-blind. The three other studies explored the effect of different treatments on QOL but did not include appropriate evaluation of cognitive function. The fifth did not report baseline data on cognitive function in the trial groups. No studies were found to be appropriate for inclusion in meta-analysis. There is no convincing evidence relating type or intensity of diabetic treatment to the prevention or management of cognitive impairment in Type II diabetes. Future research on treatments for diabetes should include standardized assessments of cognitive function as outcome measures.