Association of Subjective Cognitive Decline with Risk of Cognitive Impairment and Dementia: A Systematic Review and Meta-Analysis of Prospective Longitudinal Studies

Subjective cognitive decline (SCD) as an early pathological manifestation of brain aging has become more prevalent among older adults. We aimed to investigate the associations of subjective cognitive decline (SCD) with the combined risk of cognitive impairment and dementia. We performed a systematic review and meta-analysis via searching Embase, PubMed and Cochrane electronic databases from January 1 st 1970 to June 4th, 2020. Prospective cohort studies Healthy individuals were recruited from community, clinics and population. Healthy individuals with SCD were classified into exposure groups, while those without were considered as the reference group. Adjusted relative risks (RR) were estimated in a random-effects model. Both primary and subgroup analyses were conducted. Of 28,895 identified studies, 21 studies containing 22 cohorts were eligible for inclusion in the meta-analysis. SCD increased the risk of subsequent cognitive disorders (RR=2.12, 95% confidence intervals [CI] =1.75–2.58, I2=87%, P 15 years) subgroup and subgroup of clinics showed a higher risk of developing objective cognitive disorders. SCD is associated with an increased combined risk of cognitive impairment and incident dementia and should be considered a risk factor for objective cognitive disorders.