Conversion of subjective cognitive decline to MCI and dementia: a systematic review and meta-analysis of sex differences and risk factors.

Abstract

Objective: Subjective cognitive decline (SCD) is an important yet heterogeneous indicator of mild cognitive impairment (MCI) and dementia. Sex and health-related disparities in risk are well established, but differences in prevalence and conversion rates from SCD to MCI/Dementia by risk factor remain unclear.

Method: This preregistered study followed PRISMA guidelines to conduct a systematic review with a narrative synthesis and meta-analyses. Random-effects meta-analyses calculated the relative risk (RR) of sex, depression, hypertension, and diabetes in conversion from SCD to MCI/dementia. Q and I² statistics investigated heterogeneity. Prevalence rates were also calculated.

Results: Five cross-cultural studies (N = 1136) were eligible for the meta-analyses. Participants, on average, had less than 12 years of education. Pooled analyses showed no significant differences in the RR of conversion for depression, hypertension, or diabetes. The pooled conversion rate of SCD to MCI was 17.2% and 8.7% to dementia. Evidence of heterogeneity suggested that the aggregated data may mask differences between studies; thus, unpublished conversion rates on comorbid SCD and the health conditions are reported to inform future research.

Conclusions: Relative risk estimates align with the greater literature and extend them to an inclusive cross-cultural sample with lower education. The significant heterogeneity found underscores the complexity of the interactions between cognitive decline and modifiable risk factors. This study provides novel conversion rates to MCI and dementia for individuals with comorbid SCD and depression, hypertension, and diabetes. We recommend that sex-stratified conversion rates are reported, as limited data prevented our meta-analysis from examining this important dimension of risk.