Loneliness, Cortisol and NK Dysfunction in Chronic Stress : Psychoneuroendocrinology | May 2026

Introduction

Psychosocial stressors such as loneliness, chronic stress and social disadvantage are increasingly recognized as major contributors to cardiometabolic disease. Natural killer cell activity plays a central role in immune surveillance, inflammation regulation and cardiovascular health, yet the biological pathways linking chronic stress to NK-cell dysfunction remain incompletely understood.

Problem Statement

Although cortisol is a key neuroendocrine mediator of chronic stress through activation of the hypothalamic–pituitary–adrenal axis, its relationship with NK-cell dysfunction in humans—particularly in populations exposed to persistent psychosocial adversity—has not been clearly established. The interaction between loneliness, cortisol signalling and innate immune suppression remains poorly characterized.

Summary

This translational study explored the relationship between psychosocial stress, cortisol and NK-cell biology in African American women from under-resourced communities who were at elevated cardiovascular risk. Higher plasma cortisol levels were associated with reduced proportions of proliferative NK-cell subsets, and this relationship was strongly modified by loneliness, suggesting that social isolation amplifies cortisol-mediated immune dysregulation. Individuals with moderate-to-high loneliness demonstrated significant inverse associations between cortisol and NK-cell distribution, whereas this pattern was absent in participants with low loneliness scores. Functional analyses further demonstrated that elevated cortisol correlated with impaired NK-cell degranulation and reduced interferon-γ production, indicating compromised cytotoxic immune activity. Mechanistic experiments showed that cortisol directly suppressed NK-cell function in vitro, reducing degranulation and cytokine production while increasing PD-1 surface expression. Importantly, the study identified FABP4 as a potential mediator of this dysfunction, as inhibition of FABP4 restored PD-1 expression and NK-cell cytolytic activity. Transcriptomic profiling further supported suppression of NK-cell cytotoxic pathways in individuals with high cortisol levels. These findings provide important mechanistic insight into how chronic psychosocial stress and loneliness may impair innate immunity and potentially contribute to heightened cardiovascular and cancer risk. The study also highlights potential therapeutic relevance of targeting PD-1 and FABP4 pathways to reverse stress-associated immune dysfunction. Overall, the work establishes loneliness as a biologically relevant modifier of cortisol-driven NK-cell impairment and reinforces the growing concept that adverse social determinants of health exert direct immunometabolic effects.