Type 2 diabetes (T2D) and dementia are both diseases with increasing incidence and prevalence globally, leading to substantial economic burdens for families and society. Notably, diabetes significantly increases the risk of cognitive dysfunction, which is classified into preclinical stage, mild cognitive impairment and dementia based on the disease severity. Cognitive dysfunction is a critical contributor to disability and mortality in elderly diabetes patients. Early diagnosis and intervention are crucial for delaying disease progression, enhancing treatment efficacy, and mitigating the impact of dementia. Currently, research and clinical management of cognitive dysfunction in individuals with diabetes are in their infancy, characterized by limitations such as single-center studies, limited sample sizes, inconsistent diagnostic criteria, and insufficient data sharing. Consequently, clinical diagnosis and treatment strategies are underdeveloped, medical staff's related knowledge is lacking, and potential therapeutic targets remain unexplored. In view of these problems and shortcomings, the population cohort study is supposed to be carried out based on accurate diagnosis and constructed the high standard information and sample bank. The study will establish the standard and quality system of T2D with cognitive dysfunction cohort study (unified standards and norms). The study will integrate the standard biological samples stratified acquisition function module (homogeneity and precision) of cognitive dysfunction in T2D, and complete the construction of biological samples bank and clinical diagnosis and treatment information database. The study will apply and develop brain structural and functional imaging technology to support precision diagnosis of cognitive dysfunction in T2D.

The neuropsychological test battery are used to access the cognitive function of subjects in the study. The laboratory examinations, brain MRI and olfactory function measurements will be done in the screening period. The samples such as plasma, serum, urine and faeces et al. of the subjects will be collected in the study.

Inclusion Criteria:

• Age ≥45 years;
• Type 2 diabetes diagnosed according to the American Diabetes Association criteria;
• Willingness and ability to complete systematic neuropsychological tests;
• Understanding of the research procedures and methods, potential benefits and risks of the trial, and sign written informed consent.

Exclusion Criteria:

• Fewer than 6 years of education;
• Left-handedness;
• Dementia;
• Acute metabolic complications such as diabetic ketoacidosis, hyperglycaemic hyperosmolar state and hypoglycaemic coma within the previous 3 months;
• History or presence of neurological or psychiatric disorders;
• Presence of hypothyroidism;
• History of malignancy, or severe kidney or liver dysfunction.

This study is a dynamic prospective cohort study.