The effects of long-term cumulative HbA1c exposure on the development and onset time of dementia in the patients with type 2 diabetes mellitus: Hospital based retrospective study (2005–2021)

•Our study is the first to show the effect of cumulative HbA1c (AUCHbA1c) and mean HbA1c over time (HbA1cavg) on dementia.•Prior studies have focused on the diagnosis of T2DM or single-time HbA1c in association with development of dementia, while we examined the effects of long-term cumulative glycemic exposure.•Our study suggests poorly controlled diabetes may increase the risk of developing dementia and shorten the time to onset of dementia based on the levels of AUCHbA1c and HbA1cavg.