Landmark Clinical Trial Shows Aerobic Exercise Lowers Long-Term Cortisol, Rewiring Stress Biology
Key Insights
A one-year randomized clinical trial provides the first cause-and-effect evidence that 150 minutes of weekly aerobic exercise significantly reduces long-term cortisol levels.
The study, led by Dr. Peter J. Gianaros and Dr. Kirk I. Erickson, found a between-group difference in hair cortisol of –0.62 (95% CI: –1.14 to –0.10, p=0.039) favoring the exercise group.
Prior data from the same trial showed exercise also slowed the pace of brain aging, suggesting both chemical and structural brain benefits.
A one-year randomized clinical trial has delivered the first cause-and-effect evidence that regular aerobic exercise durably lowers the body's baseline stress setting. Published online in the Journal of Sport and Health Science on March 17, 2026, the study demonstrates that meeting the standard 150-minute-per-week physical activity guideline significantly reduces long-term cortisol levels—the body's primary stress hormone.
The trial was led by Dr. Peter J. Gianaros, Director of the Center for Mind-Body Science and Health at the University of Pittsburgh, and Dr. Kirk I. Erickson, Director of Translational Neuroscience and the Mardian J. Blair Endowed Chair of Neuroscience at the AdventHealth Research Institute (search).
"We've long known that a run can clear your head," the researchers noted, but this study is the first to map the long-term biological mechanism. "By simply meeting the standard 150-minute weekly exercise goal, participants effectively lowered the biological 'background noise' of stress."
Study Design and Population
The preregistered 12-month clinical trial enrolled 130 healthy adults aged 26 to 58 years (mean age 41.4 years; 67.7% female). Participants were randomized into two arms: an aerobic exercise group that engaged in 150 minutes of moderate-to-vigorous aerobic activity each week for a full year, and a health-information control group that received general health guidance without changing their physical activity levels.
Researchers monitored changes in cardiorespiratory fitness, cortisol, and multiple other measures of stress and emotion using brain imaging and other state-of-the-art techniques. A total of 41 participants in the exercise group and 40 in the control group completed follow-up assessments.
Cortisol Findings
In planned intention-to-treat analyses using generalized linear mixed models, a group-by-time interaction indicated that the exercise group exhibited a significant decrease from baseline to follow-up in hair cortisol relative to the control group. The between-group difference was –0.62 (95% confidence interval: –1.14 to –0.10, p(FDR) = 0.039). This reduction was also observed in per-protocol analyses.
Cortisol plays a role in numerous physiological functions including metabolism, immunity, sleep, memory, and mood regulation. Chronically elevated cortisol is linked to heart disease (search), metabolic disorders, and mental health conditions.
"The effect of exercise on long-term cortisol levels could be one of the mechanisms or benefits of exercise that protect against several diseases and some mental health conditions," said Dr. Gianaros. "But more research is needed to fully explore this possibility."
Beyond Cortisol: Brain Aging and Mental Resilience
A prior publication from the same clinical trial documented benefits extending beyond cortisol. Using advanced brain imaging techniques, the trial showed that exercise may also slow the pace of brain aging, suggesting that physical activity protects the brain's structural integrity alongside its neurochemistry.
By mitigating the adverse effects of cortisol, the 150-minute-per-week threshold appears to represent a "sweet spot" for building biological resilience against depression (search), anxiety (search), and heart disease (search), according to the researchers.
Additional Outcomes
The study also examined cardiometabolic and vascular risk factors (triglycerides, total cholesterol, high-density lipoproteins, glycosylated hemoglobin, pulse-wave velocity), autonomic activity (heart rate variability), and biomarkers of systemic and vascular inflammation (interleukin-6, intercellular adhesion molecule-1), as well as neural, cardiovascular, and subjective responses to functional magnetic resonance imaging stressor and emotion task paradigms. No other effects on these remaining outcomes were consistently observed in planned and per-protocol analyses.
Significance and Limitations
The implications are significant because most prior research in this area has been correlational and could not establish causation. The trial is also unique in its duration—no previous study had examined exercise and these specific stress biology measures over a full year.
Dr. Gianaros and Dr. Erickson expressed hope that the findings will draw more attention to how meeting the recommended 150 minutes of physical activity per week may benefit mental resilience and overall health. The study was funded by the National Institutes of Health and the National Heart, Lung, and Blood Institute (grant P01 HL040962) awarded to the University of Pittsburgh.