Abstract
To determine the risk of dementia in patients with type 1 or type 2 diabetes and in individuals with glycosylated haemoglobin, type A1C (HbA1c) of ⩾48 mmol/mol, which is the diagnostic limit for diabetes. We included the following cohorts: all incident diabetes cases aged 15 or above registered in the National Diabetes Registry (NDR) from January 2000 through December 2012 (n = 148 036) and a reference population, adult participants from the Glostrup cohort (n = 16 801), the ADDITION Study (n = 26 586) and Copenhagen Aging and Midlife Biobank (CAMB) (n = 5408). Using these cohorts, we analysed if a diagnosis of type 1 or type 2 diabetes in the NDR or HbA1c level of ⩾ 6.5% (48 mmol/mol) in the cohorts increased risk of dementia in the Danish National Patient Registry or cognitive performance assessed by the Intelligenz-Struktur-Test 2000R (IST2000R). A diagnosis of type 1 or type 2 diabetes in the NDR was associated with increased risk of dementia diagnosed both before or after age 65 as well as across different subtypes of dementia. Self-reported diabetes or high HbA1c levels were associated with lower cognitive performance (p = 0.004), while high HbA1c was associated with increased risk of dementia (HR 1.94 (1.10-3.44) in the Glostrup cohort but not in the ADDITION Study (HR 0.96 (0.57-1.61)). Both type 1 and type 2 diabetes are associated with an increased risk of dementia, while the importance of screening-detected elevated HbA1c remains less clear.
Highlights
Dementia is a broad category of diseases characterised by an irreversible decline of cognitive function
We used information from four cohorts: A nationwide, registerbased cohort with all diabetes cases registered in the National Diabetes Register (NDR) and a matched reference population (Carstensen et al, 2011), the Glostrup cohorts (Osler et al, 2011), the ADDITION cohort (Lauritzen et al, 2000), and the Copenhagen Aging and Midlife Biobank (CAMB) (Avlund et al, 2014)
When we examined dementia subtypes, the analyses of early Alzheimer’s dementia and early vascular dementia were hampered by an insufficient number of dementia outcomes
Summary
Dementia is a broad category of diseases characterised by an irreversible decline of cognitive function. Alzheimer’s disease is the most common cause of dementia, followed by vascular dementia. Several meta-analyses have reported that diabetes increases risk of Alzheimer’s Disease 1.5 times and vascular dementia 2.5 times (Cheng et al, 2012; Chatterjee et al, 2016; Zhang et al, 2017). The overall risk of dementia was increased with a relative risk of 1.65 (95% confidence interval (CI) 1.61–1.68), the risk of Alzheimer’s disease was lower (relative risk 1.10 (95% CI 1.05–1.15)) while the risk of vascular dementia was higher (relative risk 2.21 (95% CI 2.13–2.28)) (Smolina et al, 2015).
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