We systematically reviewed and summarised prospective data relating diabetes status to changes in cognitive function over time.

Published reports of longitudinal studies that described assessment of cognitive function in people with diabetes were sought. Studies were included if they assessed cognitive function in participants with diabetes at the beginning and at follow-up. Studies were excluded if they had (1) a follow-up period of less than 1 year, (2) a rate of loss to follow-up in excess of 30%, or (3) described selected subgroups. Change in cognitive function was recorded as either the mean change in score and/or the proportion of individuals developing various degrees of change in cognitive function. A pooled estimate was calculated for the latter.

Of 1,165 abstracts and titles initially identified, 25 articles met the inclusion and exclusion criteria. Individuals with diabetes had a 1.2- to 1.5-fold greater change over time in measures of cognitive function than those without diabetes. When assessed by the Mini-Mental State Exam and the Digit Symbol Span tests, a diagnosis of diabetes increased the odds of cognitive decline 1.2-fold (95% CI 1.05–1.4) and 1.7-fold (95% CI 1.3–2.3), respectively . The odds of future dementia increased 1.6-fold (95% CI 1.4–1.8).

Compared to people without diabetes, people with diabetes have a greater rate of decline in cognitive function and a greater risk of cognitive decline. Cognitive dysfunction should therefore be added to the list of chronic complications of diabetes.