Exercise, Stress, and Cardiovascular Risk
Exercise is well known to correlate with reduced risk of cardiovascular disease in human epidemiological studies. In animal studies, it is possible to demonstrate that increased physical activity does in fact cause a lower incidence of cardiovascular disease. Here researchers argue that stress has a significant effect on cardiovascular outcomes, as demonstrated by the fact that patients with greater degrees of stress, such as those with major depressive disorder, exhibit a larger beneficial correlation of reduced cardiovascular disease with exercise. It is interesting to ask which mechanisms are causing this association; exercise produces sweeping beneficial effects on body and brain, so picking apart specific contributions to an observed correlation is challenging. Yes, exercise reduces the consequences of stress, but depression tends to lead to reduced activity, and those depressed patients who are exercising were probably better off than their peers to start with. And so forth. For every proposition, there is a counterargument.
To assess the mechanisms underlying the psychological and cardiovascular disease benefits of physical activity, researchers analyzed medical records and other information of 50,359 participants from the Mass General Brigham Biobank who completed a physical activity survey. A subset of 774 participants also underwent brain imaging tests and measurements of stress-related brain activity. Over a median follow-up of 10 years, 12.9% of participants developed cardiovascular disease. Participants who met physical activity recommendations had a 23% lower risk of developing cardiovascular disease compared with those not meeting these recommendations.
Individuals with higher levels of physical activity also tended to have lower stress-related brain activity. Notably, reductions in stress-associated brain activity were driven by gains in function in the prefrontal cortex, a part of the brain involved in executive function (i.e., decision making, impulse control) and is known to restrain stress centers of the brain. Analyses accounted for other lifestyle variables and risk factors for coronary disease.
Moreover, reductions in stress-related brain signaling partially accounted for physical activity's cardiovascular benefit. As an extension of this finding, the researchers found in a cohort of 50,359 participants that the cardiovascular benefit of exercise was substantially greater among participants who would be expected to have higher stress-related brain activity, such as those with pre-existing depression. "Physical activity was roughly twice as effective in lowering cardiovascular disease risk among those with depression. Effects on the brain's stress-related activity may explain this novel observation."