Minimal Exercise May Help Prevent Future Depression

Even one hour per week of relatively low-level exercise can provide significant protection against future depression, according to a large population study published October 3 in AJP in Advance.

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“The majority of the protective effect of exercise against depression is realized within the first hour of exercise each week and was observed regardless of intensity,” wrote Samuel B. Harvey, Ph.D., an associate professor of psychiatry at the University of New South Wales in Sydney, Australia, and colleagues.

While acknowledging that higher levels of exercise are required to achieve cardiovascular benefits, the authors assert that “informing individuals that significant mental health benefits may be achieved with small changes in their behavior may be valuable in facilitating behavioral change.” Because low levels of exercise were found protective, they suggest everyday activities, such as walking or cycling, may protect against depression.

The cohort for the study consisted of more than 33,908 Norwegian adults with no symptoms of common mental disorders or limiting physical health conditions, monitored over 11 years. Participants were asked about their exercise habits and symptoms of depression and anxiety at the beginning and end of the study. Of the 22,564 individuals tracked over the study period, 1,578 (7 percent) developed case-levels symptoms of depression.

“If causality is assumed and there are no other major confounders, our results suggest that at least 12% of new cases of depression could be prevented if all adults participated in at least 1 hour of exercise each week,” Harvey and colleagues wrote.

The study did not find that exercise protected against anxiety. The prevalence of case-level anxiety at follow-up was similar regardless of the participants’ levels of baseline exercise; therefore, no association between baseline exercise levels and later case-level anxiety could be made.

In phase 1 of the study—known as the Health Study of Nord-Trondelag County (HUNT 1)—researchers asked the residents of a rural county in Norway aged 20 years or older to complete questionnaires about their lifestyles and medical histories and undergo a physical exam.

As part of the baseline exam, study participants were asked questions about symptoms of depression and anxiety, as well as how often they engaged in exercise and the intensity of their exercise. At follow-up (HUNT 2), the study participants were asked to complete the Hospital Anxiety and Depression Scale, a self-report questionnaire with 14 items covering depression and anxiety items over the previous two weeks.

Participants who reported undertaking no exercise at baseline had 44 percent increased odds of developing case-level depression compared with those who exercised one to two hours per week.

“Those who engaged in less exercise at baseline tended to have 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,” noted the researchers.

The combined physical and social benefits of exercise may mediate the protective effects against depression, according to the study.

The study was funded by the National Institute for Health Research Biomedical Research Centre at South London, Maudsley NHS Foundation Trust, and King’s College London. ■