# Age at natural menopause, reproductive lifespan and Alzheimer’s disease in females: is APOE ε4 the missing link?

## TL;DR

This study explores how age at menopause and APOE gene variants are linked to Alzheimer's disease risk in women, suggesting APOE ε4 carriers with later menopause may be at higher risk.

## Contribution

The study reveals a dose-dependent, genotype-specific interaction between reproductive aging and Alzheimer's disease risk mediated by APOE alleles.

## Key findings

- Later age at natural menopause and longer reproductive lifespan independently predict higher Alzheimer's disease risk in females.
- APOE ε4 carriers show a steeper association between later menopause and increased AD risk compared to ε3 carriers.
- APOE ε3 attenuates the risk associated with extended reproductive lifespan, while ε2 has no significant effect.

## Abstract

The apolipoprotein E (APOE) gene represents the strongest genetic determinant of sporadic Alzheimer’s disease (AD), yet its interaction with sex-specific endocrine factors remains poorly understood. Lifetime estrogen exposure, estimated through reproductive lifespan, may modulate neurodegenerative risk, but findings are inconsistent. Previous studies have examined reproductive factors and APOE interactions in relation to cognitive outcomes, but dose-dependent effects across all APOE alleles (ε2, ε3, ε4) in clinically diagnosed AD patients remain underexplored. This study investigates the joint effects of reproductive lifespan, age at natural menopause (ANM), and APOE genotype on AD risk in females.

A total of 396 female participants (103 with AD, 293 cognitively healthy controls) were retrospectively analyzed. Demographic, clinical, and reproductive data were extracted from medical records. APOE genotyping was performed by sequencing rs429358 and rs7412 polymorphisms. Logistic regression models tested associations between ANM, reproductive lifespan, and AD diagnosis, adjusting for education, body mass index (BMI), smoking, diabetes, hypertension, and number of children. Moderation analyses assessed the interaction between reproductive variables and APOE ε2, ε3, and ε4 alleles, and were followed by simple slope analyses to clarify the direction of significant effects.

AD females exhibited later ANM (50.3 ± 4.4 vs. 48.3 ± 6.2 years; p = 0.004) and longer reproductive lifespan (37.4 ± 4.4 vs. 35.4 ± 6.0 years; p = 0.005) than controls. Both ANM and reproductive lifespan independently predicted higher AD risk (adjusted OR = 1.07, 95% CI = 1.02–1.12, p < 0.01). These effects were amplified by APOE ε4 and attenuated by ε3, while ε2 showed no influence. Simple slope analyses confirmed an allele-specific gradient, with the association between later menopause and AD risk steepest in ε4 carriers and absent in high ε3 carriers.

This work provides novel evidence that extended ovarian function is associated with increased AD vulnerability in females, particularly among APOE ε4 carriers. These findings highlight a dose-dependent, genotype-specific interaction between reproductive aging and neurodegeneration, suggesting APOE as a molecular bridge linking estrogenic exposure and AD risk.