New data, collected by a team of researchers in Europe, demonstrate that engaging in physical activity or exercise prevents the onset of depression symptoms. The results, published in the American Journal of Psychiatry, do not support similar preventative effects of exercise for anxiety symptoms.
“The results presented in this study provide a strong argument in favor of further exploration of exercise as a strategy for the prevention of depression,” the authors write.
Past studies have detailed the “antidepressant effect” of exercise, finding it to be moderately effective in reducing symptoms. Less is known about the preventative effects, however, leading Dr. Samuel B. Harvey and his colleagues to explore the following questions:
- Does exercise protect against new-onset depression and anxiety?
- If so, what intensity and amount of exercise are required to gain protection?
- What causal mechanisms underlie an association between exercise and later depression and anxiety?
The study was conducted by tracking a cohort of 33,908 “healthy” adult participants over the course of 11 years and assessing their baseline and follow-up levels of depression, anxiety, and exercise engagement. A range of other details that could confound the effects of exercise on depression or anxiety were also gathered, including demographic components, substance use, and perceived social support. All data were assessed using validated measures.
Linear and logistic regression analyses were conducted, allowing the researchers to examine exercise levels at baseline in conjunction with the odds of later depression and anxiety onset. They found that higher levels of exercise at baseline corresponded to lower risk of developing depression symptoms. Those who reported engaging in no exercise at baseline were 44% more likely to develop case-level depression compared to individuals who were exercising 1-2 hours per week. Development of anxiety symptoms, however, were similar regardless of baseline exercise levels.
“In line with a priori predictions, those who engaged in less exercise at baseline tended to have a higher resting pulse, lower levels of perceived social support, and more subthreshold symptoms of depression and anxiety, and they were more likely to develop new-onset physical illnesses over the course of the study,” the authors write.
Harvey and researchers considered “reverse causation” in their model as well, accounting for cases in which anxiety or depression lead people to engage in less exercise rather than causation working in the opposite direction.
Additionally, they examined the relationships in conjunction with the data related to confounding factors. They found that levels of perceived social support, the onset of a physical illness, and symptoms of anxiety or depression that may have influenced lower levels of exercise (reverse causation) did account for some of the observed effects, but only a small proportion. By and large, the protective effect of exercise was unaccounted for by these other factors.
The researchers also observed that an exponential decay model fit better than a linear one, meaning that despite the preventative effects of exercise, beyond a certain threshold, as exercise increased, benefits decreased.
“Most of the protective effect of exercise is realized with relatively low levels of exercise, with no indication of any additional benefit beyond 1 hour of exercise each week.”
Moreover, the results demonstrated that more vigorous intensity exercise had no additional protective effects against future depression.
As for the causal mechanisms explored, the researchers put forth two hypotheses. The first, that the protective effects of exercise might be explained by confounding variables not measured in this study such as shared genetic factors, personality, or individual attitudes toward health. The other explanation explores how changes in self-esteem or serotonin release caused by physical activity may influence neurogenesis, or alterations in brain activity, particularly around areas of the brain associated with memory.
The researchers conclude that public health campaigns may be most effective if they encourage and facilitate everyday exercise activities, such as walking or biking, given levels of intensity do not influence the protective effect.
“Importantly, the majority of the protective effects of exercise against depression are realized within the first hour of exercise undertaken each week, which provides some clues regarding causation and has major implications for possible future public mental health campaigns.”
Harvey, S. B., Øverland, S., Hatch, S. L., Wessely, S., Mykletun, A., & Hotopf, M. (2017). Exercise and the prevention of depression: Results of the HUNT cohort study. American Journal of Psychiatry, appi-ajp. (Link)