1. Younger age of onset of type 2 diabetes mellitus is strongly associated with increased risk of subsequent dementia
Evidence Rating Level: 2 (Good)
Study Rundown: 34.2 million Americans (10% of the U.S. population) have type 2 diabetes mellitus, and approximately 1 in 3 American adults have pre-diabetes. While the wide variety of vascular complications of diabetes are well-documented, the association between early onset type 2 diabetes and dementia is unclear. In this prospective cohort study, over ten thousand participants were recruited in UK in 1985 to investigate the association between early development of type 2 diabetes and age of onset of dementia. Up until 2019, 710 participants developed diabetes and 639 developed dementia. The hazard ratio of dementia increased with earlier age onset of diabetes in linear fashion, suggesting that younger age at diabetes onset is linked to increased risk of subsequent dementia. One strength of this study is the precise measurements of diabetes with a more than 30 years of follow up for dementia with the help of electronic medical records. Although undiagnosed diabetes is very prevalent worldwide, this is unlikely in study given repeated clinical examinations, which also minimizes of bias from confounders. One limitation of the study, however, is that patients in longitudinal studies in general are healthier than the general population. Furthermore, the study did not delineate the various dementia etiologies and subtypes, making it impossible to ascertain the associate between type 2 diabetes and Alzheimer’s disease vs. vascular dementia, an important consideration given the association between diabetes and acute vascular events.
In-Depth [prospective cohort study]: In this prospective cohort study of 10 095 participants, 1710 participants (16.9%) developed diabetes during the follow up period between 1985 and 2019. 153 (8.9%) of the participants with diabetes subsequently developed dementia. Younger age of diabetes onset was associated with a significantly high risk of developing dementia with a fully adjusted HR of 2.14 (95% CI, 1.44-3.17) at age 55 and 1.58 (95% CI, 1.22-2.03) at age 70. Earlier age onset of dementia was also more strongly associated with development of dementia later in life.
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