Effectiveness of Exercise in Decreasing Depressive Symptoms

Growing rates of anxiety and depression, along with the associated burden and cost, represent a significant public health problem globally. However, there is a lack of consensus about how to address these issues. Analyses suggest that even with optimal treatment for all individuals with anxiety and depression disorders, the overall burden would decrease by only 35% to 50%.¹

Although attention has increasingly turned toward potential strategies for prevention, many of the “known risk factors for depression and anxiety, such as familial risk, socioeconomic position, and life events, are difficult or impossible to modify,” wrote the authors of new research published in the American Journal of Psychiatry.² “There is, however, some emerging evidence that lifestyle factors, such as physical inactivity, may be potential targets for strategies aimed at” prevention.^3,4

Cross-sectional associations have been noted between exercise and reduced rates of depression and anxiety, although findings from prospective studies have varied, with some showing a link and others reporting no such link. There is a more established body of evidence that supports the moderate effectiveness of exercise to decrease depressive symptoms.^5,6 Conclusions are less clear regarding the benefits of exercise as a preventive measure for new-onset depression and anxiety, including the recommended amount and intensity of exercise.⁷

In addition, the proposed mechanisms underlying any preventive effects have not been elucidated, although some evidence points to alterations in autonomic nervous system (ANS) activity as one such pathway. “Regular exercise increases parasympathetic vagal tone, leading to physiological changes such as resting bradycardia,” the authors explain in the study.⁸ Altered ANS functioning has been found in patients with depression, and vagal nerve stimulation has been shown to treat depression effectively in some cases.⁹ Other mechanisms may include social benefits of exercise and improvements in self-esteem and overall physical health.

“Addressing the uncertainty surrounding the relationship between exercise and depression and anxiety is important,” said the authors. “While many agencies are keen to promote the potential mental health benefits of exercise, at present the literature is unable to provide the most basic information needed for effective, targeted, evidence-based public health campaigns concerning depression and anxiety.”

To that end, the current prospective cohort study sought to determine whether exercise protects against new-onset depression and anxiety, and if it does, what the required “dose” and underlying causal mechanisms might be. The initial cohort consisted of 33,908 healthy adults in Norway, with “healthy” defined here as having no evidence of depression, anxiety, or limiting physical illness. These measures were assessed at baseline using the 12-item Anxiety and Depression Symptom Index as well as through direct questioning. Participants also reported the frequency, duration, and intensity of exercise at baseline.

The follow-up period ranged from 9 to 13 years, and 22,564 of the original participants completed the follow-up assessment, which was the self-report Hospital Anxiety and Depression Scale to indicate symptoms of depression and anxiety from the previous 2 weeks. Various confounding and mediating variables were also considered in the data analyses.

Of the participants remaining at follow-up, clinical symptoms of depression developed in 7.0%, and clinical anxiety symptoms developed in 8.7%. The results demonstrate that regular exercise was associated with reduced risk for new-onset depression but not for new-onset anxiety. A negative relationship was observed between the amount of exercise reported at baseline and the risk for depression developing (P =.001).

Most of the protective benefit occurred within the first hour of exercise undertaken each week, regardless of exercise intensity. The findings further suggest that if all participants had engaged in exercise for at least 1 hour per week, and if the relationship is causal, 12% of cases of new-onset depression could have been prevented.

After adjustment for confounding variables, the odds for depression developing were 44% higher (95% CI, 17%-78%) among those who indicated no exercise at baseline compared with those who reported 1 to 2 hours of exercise per week. Additionally, there was no evidence of interaction by age or gender in the link between the amount of exercise and the subsequent onset of depression or anxiety.

The physical health and social benefits of exercise were determined to account for a small proportion of its protective effect, whereas biologic mechanisms, such as ANS alterations, did not explain this effect.

This study is the largest and most thorough investigation of the prospective dose-response relationship between exercise and later onset of depression. The present results are in line with previous findings that significant mental health benefits may derive from moderate amounts of exercise.⁶

“Relatively modest changes in population levels of exercise may have important public mental health benefits and prevent a substantial number of new cases of depression,” the authors concluded. As such, “it may be that the most effective public health measures are those that encourage and facilitate increased levels of everyday activities, such as walking or cycling.” Future research should continue to explore the effects of exercise as a potential strategy for the prevention of depression.

References

1. Andrews G, Issakidis C, Sanderson K, Corry J, Lapsley H. Utilising survey data to inform public policy: comparison of the cost-effectiveness of treatment of ten mental disorders. Br J Psychiatry. 2004;184:526-533.
2. Harvey SB, Øverland S, Hatch SL, Wessely S, Mykletun A, Hotopf M. Exercise and the prevention of depression: results of the HUNT Cohort Study [published online October 3, 2017]. Am J Psychiatry. doi:10.1176/appi.ajp.2017.16111223
3. Teychenne M, Ball K, Salmon J. Physical activity and likelihood of depression in adults: a review. Prev Med. 2008;46:397-411.
4. Schuch FB, Vancampfort D, Sui X, et al. Are lower levels of cardiorespiratory fitness associated with incident depression? A systematic review of prospective cohort studies. Prev Med. 2016;93:159-165.
5. Cooney GM, Dwan K, Greig CA, et al. Exercise for depression. Cochrane Database Syst Rev. 2013;(9):CD004366.
6. Rosenbaum S, Tiedemann A, Sherrington C, Curtis J, Ward PB. Physical activity interventions for people with mental illness: a systematic review and meta-analysis. J Clin Psychiatry. 2014;75:964-974.
7. Mammen G, Faulkner G. Physical activity and the prevention of depression: a systematic review of prospective studies. Am J Prev Med. 2013;45:649-657.
8. Seals DR, Chase PB. Influence of physical training on heart rate variability and baroreflex circulatory control. J Appl Physiol. 1989;66:1886-1895.
9. Rottenberg J. Cardiac vagal control in depression: a critical analysis. Biol Psychol. 2007;74:200-211.