Exercise Duration Modulates Cortisol Release and Chronic Cortisol Exposure Jeopardises T Cell Effector Functions

Psychological stress has been linked to increased incidence and mortality of cancer. During stress, cortisol is released into circulation and regulates cellular processes including immune activity by acting on glucocorticoid receptors (GCRs) expressed by target cells. Chronic stress-induced cortisol has been suggested to promote tumour progression and compromise the efficacy of cancer treatments. Conversely, cortisol is also transiently secreted during exercise. Although exercise has been suggested to have beneficial effects against cancer, the impact of exercise-elevated cortisol on immune cell functions remains poorly understood. Here we studied the dynamics of cortisol secretion following exercise and how cortisol affects effector functions of T cells in the context of acute versus chronic stress. We show that 40 min of acute, high-intensity exercise in healthy adults significantly increased stable circulating cortisol levels whereas a 5-min sprint failed to. Acute exposure to cortisol for 4 h showed no negative effects on the proliferation, cytokine release, or killing activity of human CD3⁺ T cells. In contrast, chronic cortisol dampened these T cell effector functions. Furthermore, chronic cortisol exposure induced the proliferation of several cancer cell lines. Our findings highlight the opposing effects of cortisol during acute stress, such as exercise, compared to chronic stress, on cancer cells and T cells. This suggests an important potential in targeting cortisol signalling to enhance cancer immunotherapy.