Type 2 diabetes mellitus (DM) is a risk factor for cognitive decline, but evidence from Irish population-based studies is lacking. The aim of this work was to investigate the association between DM and the risk of cognitive decline in the Irish Longitudinal Study on Ageing (TILDA).

This is a longitudinal cohort study, totalling a 6-year follow-up.

TILDA is a nationally representative observational study of community-dwelling adults over 50 years old.

DM was assessed via self-reported medical diagnosis. Cognition was assessed with Montreal Cognitive Assessment (MoCA, baseline and wave 3) and the Mini-Mental State Examination (MMSE, all waves) total score and error count. We incorporated individuals’ variability as a random effect and used zero-inflated mixed-effects to model MMSE error counts as a function of DM longitudinally. The model was adjusted for age, sex, history of stroke, hypertension, and any emotional, nervous, or psychiatric problems.

A total of 3,687 participants were evaluated. At baseline, the prevalence of diabetes was 6.4%. Participants with DM had significantly lower MoCA and MMSE scores and higher error counts than those without DM. Age, male sex, DM, stroke, and hypertension were significantly associated with higher error counts in MMSE at baseline. Over six years, DM was significantly associated with an accelerated decline in cognition.

Having DM predicted cognitive decline in TILDA participants over 6-years. These findings corroborate the importance of screening and managing DM in community-dwelling older adults to prevent future cognitive impairment.