Validation of subjective cognitive decline and its association with registry-based dementia diagnoses

Abstract Background Subjective cognitive decline (SCD) is increasingly recognized as an early indicator of dementia. However, survey-based measures of memory, learning, and concentration have rarely been evaluated against register-verified dementia outcomes. We examined the internal structure of a composite SCD measure and its association with registry-based dementia diagnoses and medications. Methods We used data from Phases 4 (2017, N = 6832, age 55-77, 81% women) and 5 (2022, N = 5950, age 60-82) of the Helsinki Health Study, with 76% and 88% of participants consenting to register linkage. SCD was assessed through self-reported declines in memory, learning, and concentration. Dementia diagnoses (ICD-10) and medications (ATC) were retrieved from national health registers. Associations with register-verified dementia were analyzed using age-adjusted binomial regression (PRs, 95% CIs), and discriminatory ability was described using Receiver Operating Characteristic (ROC). Associations with lifestyle factors, chronic conditions, and RAND-36 functioning were also examined. Results Across phases, 32% reported memory decline, 48% learning, and 31% concentration. High cross-correlations (r≈0.57-0.60) and Cronbach's alphas (0.79-0.81) supported internal consistency. The composite score was associated with dementia diagnoses and showed moderate discriminatory ability (AUC =0.74-0.79). SCD was associated with 2.4-4.3 times higher dementia prevalence and to adverse lifestyle factors, chronic health conditions, and lower health-related quality of life. Conclusions Our findings indicate that SCD is statistically associated with registry-based dementia diagnoses and several indicators of poor health. SCD items may contribute to identifying population subgroups with elevated dementia prevalence and inform future research on early indicators of cognitive decline. Key messages • Subjective cognitive decline is statistically associated with registry-based dementia diagnoses in older adults. • Self-reported SCD items may help identify individuals with increased likelihood of dementia in survey-based research.