Effect of the treatment of Type 2 diabetes mellitus on the development of cognitive impairment and dementia

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Dementia is a global healthcare concern. Type 2 diabetes mellitus — a form of diabetes which becomes commoner with older age — increases the risk of developing dementia. Type 1 diabetes, which typically begins earlier in life, is always treated with insulin; but there are a variety of different ways of treating Type 2 diabetes, including lifestyle changes and different medications. We wanted to find out if some ways of treating Type 2 diabetes were better than others in terms of preventing either dementia or less serious decline in cognition (memory and other thinking skills).

What we did

We searched medical databases for clinical trials in which participants had been assigned at random to different treatments for Type 2 diabetes and in which cognition had been measured at the beginning and end of the trial. We were only interested in treatments for Type 2 diabetes which are recommended by international clinical practice guidelines (CPGs). We analysed data from the studies we found, looking for effects on dementia and cognition, death rates and the side effect of hypoglycaemia, which is when blood glucose levels fall too low and which can be a result of treatment.

Key results

We found seven randomised trials suitable for inclusion in this review, but we could only get data on cognition from four of them. Of these, the two larger studies had a total of 13,934 participants and compared a standard treatment strategy with a more intensive strategy which aimed to keep blood glucose lower. Two smaller studies, which each had approximately 150 participants, compared different drug treatments, but in both studies one of the treatments was a drug which is not generally considered suitable for older patients. We found no good evidence that any of the treatments in these studies was clearly superior to any other for preventing dementia or cognitive decline. An intensive treatment strategy was more likely than standard treatment to cause hypoglycaemia, but there were no differences in death rates.

Quality of evidence

We judged the quality of the evidence for all outcomes to be low or moderate due to risk of bias in the included studies, small sample sizes, and imprecise estimates of the effects. This means that our confidence in the results is limited.