Sunday, May 09, 2010

Elisabeth Wolff, MA; Andreas Ströhle, MD - Causal Associations of Physical Activity/Exercise and Symptoms of Depression and Anxiety

http://binbrain.com/blog/wp-content/uploads/2008/05/aerobic-exercise.jpg

This is a letter to editors from The Archives of General Psychology - the authors make a good point about a recent article that seemed to disprove the benefits of exercise for anxiety and depression.

The full text of the original article, "Testing Causality in the Association Between Regular Exercise and Symptoms of Anxiety and Depression" (Marleen H. M. De Moor, MSc; Dorret I. Boomsma, PhD; Janine H. Stubbe; Gonneke Willemsen, PhD; Eco J. C. de Geus, PhD) is free online.
Causal Associations of Physical Activity/Exercise and Symptoms of Depression and Anxiety

Elisabeth Wolff, MA; Andreas Ströhle, MD

In their article1 published in August 2008, De Moor and colleagues demonstrated that although regular exercise in the general population is associated with reduced anxiety and depression, this correlation is not a causal effect of exercise, as is often implicitly assumed in population-based studies and has been reported from several clinical studies.2 Using an elegant design with cross-sectional and longitudinal data from monozygotic and dizygotic twin pairs, De Moor and colleagues were able to disprove this assumption of causality in a large sample. Instead, they found that there are common genetic factors influencing both exercise behavior and anxious or depressive symptoms.1

Because this constitutes a very important finding that certainly will be broadly cited, we would like to point out 2 aspects that might be overlooked in light of this excellent study. The most important limitation of the study's conclusion about the absence of causal effects of exercise on anxiety and depression is already mentioned by De Moor and colleagues themselves: the fact that the common genetic factors they found only affect leisure-time exercise, ie, voluntary and intentional exercise training. However, this is a rather tight definition of physical activity, in which not even conscious motor activity such as biking or brisk walking to work is considered. As reported, the distribution of the resulting "metabolic equivalent task hours" used as a measure of exercise is skewed. The majority of people do not "exercise" at all. If the definition of exercise was broadened to "physical activity" in a more general sense, the distribution in the population would surely draw nearer a normal distribution. In line, the recommendations for physical activity have shifted in the last decade: until 1995 the focus of public health recommendations was on 3 to 5 exercise bouts per week. Afterward, the Centers for Disease Control and Prevention, the American College of Sports Medicine, and the American Heart Association started recommending moderate-intensity aerobic (endurance) physical activity for a minimum of 30 minutes on 5 days each week or vigorous-intensity aerobic physical activity for a minimum of 20 minutes on 3 days each week to promote and maintain physical and psychological health.3-4 Following this shift in public health recommendations, standardized instruments for the assessment of physical activity independent of the context (sports, at home, for transportation, at work) have been developed, for example, the International Physical Activity Questionnaire.5

Another important point is that the findings of the present study do not conflict with clinical trials that found antidepressant or anxiolytic activity of (prescribed) exercise training in healthy subjects and in patients with anxiety or depressive disorders.2 Thus, the finding that in the general population there is no causal relationship between leisure-time exercise and symptoms of anxiety or depression does not exclude that (1) everyday physical activity such as labor, walking or biking to work, and gardening may prevent or improve symptoms of anxiety and depression and (2) prescription of physical activity as preventive or therapeutic intervention for psychiatric patients with anxiety or affective disorders may cause beneficial effects for mental health.


AUTHOR INFORMATION


Correspondence: Dr Ströhle, Department of Psychiatry and Psychotherapy, Campus Charité Mitte, Charité–Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany (andreas.stroehle@charite.de).

Financial Disclosure: None reported.

Author Affiliations: Department of Psychiatry and Psychotherapy, Campus Charité Mitte, Charité–Universitätsmedizin Berlin, Berlin, Germany.

1. De Moor MH, Boomsma DI, Stubbe JH, Willemsen G, de Geus EJ. Testing causality in the association between regular exercise and symptoms of anxiety and depression. Arch Gen Psychiatry. 2008;65(8):897-905. FREE FULL TEXT

2. Ströhle A. Physical activity, exercise, depression and anxiety disorders. J Neural Transm. doi:10.1007/s00702-008-0092-x. 2009;116(6):777-784. FULL TEXT | WEB OF SCIENCE | PUBMED
3. Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchner D, Ettinger W, Heath GW, King AC; et al. Physical activity and public health: a recommendation from the centers for disease control and prevention and the American College of Sports Medicine. JAMA. 1995;273(5):402-407. FREE FULL TEXT
4. Haskell WL, Lee IM, Pate RR, Powell KE, Blair SN, Franklin BA, Macera CA, Heath GW, Thompson PD, Bauman A. Physical activity and public health: updated recommendations for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc. 2007;39(8):1423-1434. FULL TEXT | WEB OF SCIENCE | PUBMED
5. Craig CL, Marshall AL, Sjöström M, Bauman AE, Booth ML, Ainsworth BE, Pratt M, Ekelund U, Yngve A, Sallis JF, Oja P. International Physical Activity Questionnaire: 12 country reliability and validity. Med Sci Sports Exerc. 2003;35(8):1381-1395. FULL TEXT | WEB OF SCIENCE | PUBMED

Arch Gen Psychiatry. 2010;67(5):540-541.


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