The Dementia UK report, published earlier this year on behalf of the Alzheimer’s Society, predicts that by 2050, 34 million people worldwide will have dementia, and 71% of these people will live in developing countries.1 Currently, nearly 700 000 people have dementia in the United Kingdom, and worldwide this figure approaches 18 million. Dementia costs the UK economy around £17bn (€24bn; $35bn) each year, but the human cost to patients, their families, and their friends is incalculable.

Over the past 15 years, several studies have indicated that diabetes mellitus, particularly type 2 diabetes, is associated with an increased risk of cognitive impairment and dementia.234 If these studies are correct, then the future burden of dementia may be even greater than estimated as the prevalence of type 2 diabetes continues to rise.

Early data that linked type 2 diabetes with cognitive impairment came from cross sectional cohort studies that were generally of poor methodological quality.4 However, a recent systematic review of prospective observational studies identified 25 articles that assessed the …