Background

Left-right hippocampal volumetric asymmetry and atrophy are implicated in neurodegenerative and neuropsychiatric disorders, yet their molecular basis in healthy adults remains poorly understood.

Methods

We conducted a meta-analysis of epigenome-wide association studies across six population-based cohorts (n = 8156; 53% women; mean age = 60.7 years) to identify DNA methylation signatures associated with left and right hippocampal volumes (LHCV, RHCV) and hippocampal asymmetry (i.e, differences between left and right volumes divided by their sums).

Findings

We identified five CpGs and 262 differentially methylated regions associated with LHCV, nine CpGs and 246 regions with RHCV, one CpG and 16 regions with asymmetry. Cross-omics integration uncovered 15 LHCV-related and 13 RHCV-related methylation-gene expression pairs, with five overlapping genes primarily involved in immune regulation. LHCV-specific genes were involved in cellular signalling, and Mendelian randomisation (MR) analyses supported a potential causal association between brain expression of DIP2C and increased risk of major depressive disorder. RHCV-specific genes were involved in neuronal differentiation pathways, with MR analyses suggesting that brain-tissue expression of BAIAP2, MACF1, SLC16A5, and CORO1B was associated with neuropsychiatric disorders. We also identified sex-specific patterns with hippocampal asymmetry. Notably, baseline methylation at these sites predicted hippocampal atrophy rates, explaining >10% of the variation. Associations with multiple healthy dietary patterns suggest modifiable influences on hippocampal structure.

Interpretation

These findings highlight distinct methylation profiles as potential biomarkers or therapeutic targets for neuropsychiatric and neurodegenerative conditions.

Funding

Institutional funds, Federal Ministry of Education and Research of Germany, Alzheimer’s Association.

Copyright © 2026 The Authors. Published by Elsevier B.V. All rights reserved.