The complex interplay between cognitive reserve, age of diagnosis and cognitive decline in Alzheimer's disease: a retrospective study.

Objective: The present study examined the cognitive reserve (CR) theory at late stages of Alzheimer's disease (AD). The objective is to replicate previous studies and examine the complex role of education and family size as indicators of CR.

Participants and methods: This is a retrospective study included 642 patients diagnosed with AD after age 65, categorized into low education (LE, ≤ 8 years, n = 141) and medium-high education (MHE, ≥ 9 years, n = 442) groups. Participants were followed up longitudinally using the Mini Mental State Examination.

Results: Higher education in the MHE group, but not in the LE group, correlated with delayed diagnosis. In both groups, higher education correlated with accelerated cognitive decline. In the MHE group, country of origin was associated with cognitive decline, while in the LE group, it was linked to family size.

Conclusions: This study shows that in patients with MHE but not in LE, higher education resulted in delayed diagnosis. Conversely, in cases of LE, this measure may not fully reflect CR and abilities. Additionally, higher education was associated with faster deterioration, a finding that has not been replicated often in the literature. The study illustrates the complex impact of CR proxies on age of diagnosis and cognitive decline.