Research reportPhysical activity, exercise coping, and depression in a 10-year cohort study of depressed patients
Introduction
Epidemiological studies of community samples have shown that individuals who engage in more physical activity are less likely to be concurrently depressed (Farmer et al., 1988, Kritz-Silverstein et al., 2001, Strawbridge et al., 2002). For example, Camacho, Roberts, Lazarus, Kaplan, and Cohen (1991) found that, after adjusting for age, gender, and physical disability, individuals with low activity levels were at much greater risk for depression compared to a high-activity reference group (adjusted OR = 4.22, 95% CI: 3.17,5.62). Similarly, Kritz-Silverstein, Barrett-Connor, and Corbeau (2001) found that more intensive and frequent activity was associated with lower scores on the Beck Depression Inventory (BDI). Although the mechanisms and causal direction underlying the link between physical activity and depression are unknown, numerous pathways have been hypothesized, such as increased serotonin and endorphins, associated increases in hardiness, reduced stress reactivity, and activity-related increases in control, mastery, and self-efficacy (Paluska and Schwenk, 2000).
Evidence for the protective effect of physical activity on subsequent depression has been mixed. At least four studies using community samples have failed to find a protective effect of physical activity for subsequent depression (Cooper-Patrick et al., 1997, Kritz-Silverstein et al., 2001, Lennox et al., 1990, Weyerer, 1992). For example, Kritz-Silverstein et al. (2001) found no association between baseline exercise and either BDI scores or changes at a 5-year follow-up. However, several studies have found long-term protective effects of physical activity (Camacho et al., 1991, Farmer et al., 1988, Paffenbarger et al., 1994, Strawbridge et al., 2002). For example, among non-depressed women, Farmer et al. (1988) found that more recreational physical activity at baseline independently predicted less depressive symptoms eight years later.
Several potential explanations exist for these inconsistencies. One issue is that researchers have used quite diverse measures of physical activity, exercise, and depression. For example, definitions of physical activity have ranged from gardening to participation in strenuous sports. Another issue is that prior longitudinal studies have typically examined of physical activity and depression at only two assessment periods. The hazards of estimating longitudinal relationship with only two waves of data have been elaborated elsewhere (Rogosa, 1988). Utilizing more than two waves of data yields greater precision and reliability in estimating longitudinal associations (Singer and Willett, 2003).
The present study addresses these issues, as well as other gaps in the epidemiological literature linking physical activity and depression. Our primary goal was to examine the nature and magnitude of the association between physical activity and depression in initially depressed patients. This relationship has been overlooked in the epidemiological literature, is of substantial clinical interest, and has implications for treatment and relapse-prevention. To date, virtually all of the epidemiological studies have used community-based (non-patient) samples and have excluded depressed individuals. Although these studies are informative about the potential protective effects of physical activity on the onset of depression, they do not address the potential therapeutic effects of physical activity for people who are already depressed. Therefore, we focused on patients who were depressed at baseline.
Second, previous studies have assessed the type and frequency of physical activities, but have not considered the personal meaning or function of the activities. If the mechanisms by which physical activity affects depression involve the personal meaning or motivation for activities, then the failure to consider these constructs may introduce noise (unreliability) into estimations of effects. For example, physical activity that is used to help cope with distress may be more closely associated with depression than physical activity motivated by social contact or attempts to lose weight. To begin to address this issue, we consider the influence of exercise as a strategy for coping with a recent stressful event on depression.
Third, we examine individual depression trajectories using mixed-effects regression models. This approach enables us to assess longitudinal effects across four waves of data. To address questions about the correlates of change in depression, growth-curve modeling provides a precise, reliable, powerful, and statistically accurate method (Rogosa, 1988, Rogosa and Willett, 1985, Singer and Willett, 2003, Willet, 1988).
Fourth, most prior studies have examined only the main effects of physical activity on depression. Although a few studies have considered the buffering effect of physical activity on the relationship between stress and depression or stress and anxiety (Carmack et al., 1999, LaPerriere et al., 1990), none have done so in depressed patients. Therefore, in addition focusing on the main effects of physical activity and depression, we examine buffering hypotheses captured in the following question: Does physical activity or exercise coping reduce the strength of associations between negative life events or health status and depression? Clinically, support for these hypotheses could inform prescriptions of physical activity as a buffer against the impact of negative life events on depression. We also checked the reverse causation hypothesis, that is, whether depression status predicts change in physical activity.
Our final goal was to provide evidence that might corroborate the results of recent randomized controlled trials (RCTs; e.g., Dunn et al., 2005) suggesting that interventions to increase physical activity are a feasible and effective strategy for treating mild to moderate depression. Congruence between findings from RCTs and observational studies should strengthen confidence in the results obtained from both types of studies. Evidence from naturalistic observational studies that supports the findings of RCTs suggests that results from RCTs may generalize beyond the selected individuals willing to participate in them.
Section snippets
Patient sample
This research is part of an ongoing longitudinal study of depression. The overall study is examining the factors than influence the naturalistic course of depression. Participants (n = 424) were patients entering one of five facilities for the treatment of depression, including two community mental health centers, a health maintenance organization, a university hospital, and a Department of Veteran Affairs Medical Center. All patients were over 18 years old and met Research Diagnostic Criteria
Results
The numbers of patients at the 1, 4, and 10-year follow-ups were 395, 370, and 313, respectively, roughly a 90% wave-to-wave retention rate of surviving patients. One of the advantages of the multilevel modeling strategy is that data from all 424 patients could be included in the analysis. However, we checked whether those patients who provided data only at baseline differed in any systematic way from patients who provided data at two or more assessments and found no differences on any of
Discussion
In this sample of initially depressed patients, higher physical activity was associated with less concurrent depression at 4 assessments spanning 10 years. The cross-sectional association between physical activity and depression could not be explained by age, medical problems, or the presence of negative life events in the previous 3 months. Higher physical activity also counteracted the effects of medical conditions and negative life events on depression. However, although higher levels of
Acknowledgement
Preparation of this article was supported by the Department of Veterans Affairs Health Services Research and Development Service and Office of Academic Affiliations. The views expressed here are the authors' and do not necessarily represent the views of the Department of Veterans Affairs.
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