Occupational circadian disruption and brain structure: evidence from normative developmental brain lifespan trajectories

Shift work disrupts circadian rhythms and is associated with adverse health outcomes. However, its effects on structural differences in the brain remain unclear. We applied the normative brain lifespan chart methodology to evaluate whether shift workers exhibit neuroanatomical deviations from age- and sex-specific reference trajectories. We analyzed structural brain magnetic resonance imaging (MRI) data from 111 healthcare workers comprising 33 shift workers and 78 nonshift workers recruited from a tertiary hospital in South Korea. Six global brain metrics, namely ventricular volume, gray matter volume, white matter volume, subcortical gray matter volume, cortical surface area, and cortical thickness, were extracted using FreeSurfer 7.4. The brain structures of the participants were benchmarked against the normative reference distributions derived from 123,984 MRI scans. Group differences were examined using multiple linear regression models, adjusted for age and intracranial volume. Sex-stratified and regional analyses were conducted to identify the potential occupational neuroplasticity patterns. Global brain metrics showed no significant differences between shift and nonshift workers after adjusting for covariates. However, sex-stratified analyses revealed that female shift workers exhibited nominally lower gray matter volumes (p = 0.002) and higher cortical surface areas (p = 0.008) than did nonshift workers in unadjusted analyses. These associations were attenuated after adjusting for age and the intracranial volume. Regional analyses that did not survive multiple comparison correction suggested sex-specific spatial patterns. Male shift workers showed elevated prefrontal and parietal volumes compatible with executive function demands, whereas female shift workers displayed reduced limbic and occipital volumes, suggesting altered emotional processing. This study represents the application of normative brain lifespan charts in occupational neuroscience. Although global structural measures showed null findings, sex-specific patterns suggested that occupational neuroplasticity may manifest through functional reorganization rather than macrostructural brain deviation. Future multimodal investigations that integrate functional neuroimaging, circadian biomarkers, and neurocognitive assessments are warranted.