Relationship between type 2 diabetes mellitus and cognitive decline: a 4-year prospeciive cohort study

Objective Toinvestigate the relationship between type 2 diabetes mellitus (T2DM) and cognitive decline.Methods Data were obtained from the cognitive impairment cohort of middle-aged and elderly population in rural areas of Xi'an City. The cohort consisted of residents aged 40 years and older in two villages of Huyi District, Xi'an. The baseline survey was completed between October 2014 and March 2015, with two follow-up visits in 2016 and 2018. The present study was conducted on cognitively normal people at baseline. Individual characteristics, lifestyle, and medical history were collected; physical and biochemical examinations were completed. According to medical history of T2DM and fasting blood glucose, the study population was divided into non-T2DM group, pre-existing T2DM group, and new-onset T2DM group.The Mini-Mental State Examination (MMSE) was used to assess global cognitive function.Participants with a drop of ≥2 points in MMSE score from baseline after 4 years were defined as having cognitive decline. Chi-square test and multivariate Logistic regression analysis were employed to analyze the effect of T2DM status on the risk of cognitive decline.Results A total of 1350 subjects completed the follow-up.In the follow-up population, 1096 (81.2%) were free of T2DM, 158 (11.7%) already had T2DM at baseline, and 96 (7.1%) developed new-onset T2DM during the follow-up.Cognitive decline was observed in 230 individuals after 4 years, representing 17.0% of the study population. The new-onset T2DM group had the highest 4-year incidence of cognitive decline (non-T2DM group vs. pre-existing T2DM group vs. new-onset T2DM group：15.7%vs.20.9%vs.26.0%, P=0.014), and the incidence of cognitive decline in the newly-onset T2DM group was significantly higher than that in the non-T2DM group (P=0.009). Multivariate Logistic regression analysis showed that the new-onset T2DM group had an increased risk of cognitive decline compared with the non-T2DM group within 4 years (OR=1.726, 95%CI ：1.029-2.896, P=0.039).However, no significant difference in 4-year risk of cognitive decline in the pre-existing T2DM group was observed (OR=1.402, 95%CI ：0.890-2.210, P=0.145). Conclusion Through the 4-year follow-up study of cognitively normal adults aged 40 and above in rural Xi'an, it was found that new-onset T2DM patients face a significantly elevated risk of cognitive decline, suggesting that cognitive decline may occur in the early stage of T2DM.