For a study, the researchers sought to determine if a history of clinical depression was linked to dementia later in life while adjusting for observed sociodemographic characteristics and unobserved factors shared by siblings and to determine if gender, educational level, and marital status affect the relationship. Between 2001 and 2018, researchers used administrative healthcare data to perform a national cohort study of 1,616,321 people aged 65 and up. In the 15–30 years before dementia follow-up, a history of depression was discovered in the national hospital registry. To investigate the link between a history of depression, sociodemographic variables, and dementia, researchers employed conventional and sibling fixed-effects Cox regression models. In the traditional Cox model, a history of depression was associated with an adjusted hazard ratio of 1.27 (95% CI 1.23–1.31) for dementia and 1.55 (95% CI 1.09–2.20) in the sibling fixed-effects model. Depression was linked to a higher incidence of dementia across all educational levels (test for interaction, P=0.84). Still, the link was less for widowed people than married people (P=0.003) and stronger for males than women (P=0.006). Following covariate correction, the increased risk among men was reduced (P=0.10). According to a study, a history of depression was consistently linked to a higher risk of dementia later in life. The outcomes back up the theory that depression plays a role in dementia etiology.