In 104 older adults (mean age 73.8; 60 female), greater social network size—measured via the Social Network Index—was linked to lower cortisol and better attention and executive function in men, while in women the same larger networks correlated with higher perceived stress, smaller hippocampal volume, and lower episodic memory performance. Both sexes gained perceived social support from broader networks, yet the downstream biological and cognitive signatures diverged sharply by sex.
This is a genuinely disruptive finding for the cognitive-reserve field, which has largely treated social engagement as a uniformly protective factor. The stress-biology pathway offers a plausible mechanism: women disproportionately absorb caregiving and social-coordination burdens—what sociologists call 'emotional labor'—so a larger network may translate into greater role obligations rather than greater resource buffering. Chronically elevated cortisol is well established as a driver of hippocampal atrophy, making the hippocampal volume difference biologically coherent rather than incidental.
Critical caveats: the sample is small (n=104), cross-sectional, and drawn from a single French cohort, so causality and generalizability remain open questions. Hippocampal volume differences could reflect pre-existing structural variation rather than network-driven change. Still, the convergence across cortisol, hippocampal volume, and cognitive domain scores strengthens the internal consistency. For practitioners, the takeaway is clear: blanket advice to 'stay socially active' needs sex-stratified nuance, prioritizing quality and role-burden assessment over raw network size—especially for older women.