In this prospective study of mothers followed through 12 months postpartum, we found that the association between MVPA and postpartum depressive symptoms varied according to the domain/type of physical activity. There was some evidence of increased odds of having elevated depressive symptoms as a result of participation in any MVPA. Women who participated in adult and child care, indoor household, and work MVPA at 3 months postpartum were more likely to have elevated depressive symptoms at 12 months postpartum. There was no association between recreational and outdoor household MVPA and depressive symptoms.
Our results differ from previously published research in that recreational MVPA, or any other domain of MVPA, was not associated with a decrease in the odds of depressive symptoms. Nine of the ten previous studies of physical activity and depressive symptoms in postpartum women found that physical activity participation improves depressive symptoms.15–18,20–24
Seven of these ten studies were intervention trials.15–21
Though most of the studies examined the effects of physical activity on depression over time, one study examined the acute impact of physical activity on depressive symptoms.18
Interventions were varied, including walking with a stroller, regular supervised exercise sessions, and home-based exercise training and support. Both intervention and observational studies focused on walking or recreational activity and did not address differences by physical activity domain. Two of the nonintervention studies were cohorts of pregnant women who were followed into postpartum. Herring et al.23
found that women with PPD walked significantly less than women without antenatal depression or PPD. Haas et al.24
found that women who were inactive postdelivery were 1.62 times more likely to have elevated depressive symptoms in comparison to women participating in >2 hours/week of activity. Craike et al.22
found a significant inverse association between leisure time MVPA and depressive symptoms in a prospective cohort of Australian women with infants aged 3–19 months. Daley et al.19
reported the only study to find no effect of an exercise trial on depressive symptoms, but the authors state that the study was not powered to determine such an effect.
Few studies have addressed the association between physical activity domain and depression. We found no studies using postpartum women that have done so, but there has been some research among nonpregnant women. McKercher et al.52
compared the association between physical activity and depression among young men and women and found that leisure activity was associated with decreased prevalence of major depression, and work activity was associated with increased prevalence among women. No associations were found among men. Teychenne et al.53
investigated how the association between physical activity and depressive symptoms differed by domain among 1501 Australian women. They found that women participating in >3.5 hours of leisure time physical activity per week had lower odds of depressive symptoms but no significant association in any other domain (work, transportation, or domestic). These studies demonstrate that domain can influence physical activity-depression associations.
To date, there has been little explanation as to why the association between physical activity and depression may differ by domain. It has been suggested that it may be due to adverse, unfavorable, or unhealthy conditions in which the activity typically is performed.54
For example, those with high levels of work activity may be conducting a great deal of strenuous activity over long hours on the job, and those performing household activities may be performing repetitive tasks.54,55
The benefits of physical activity may be countered by these adverse conditions. Another possible explanation is that different types of activity may serve as stressors or burdens that may contribute to the development of depressive symptoms. We suspect that performing involuntary physical activity (i.e., to perform housework or as part of a job) may be stressful, therefore contributing toward elevated depressive symptoms rather than alleviating them. Individuals who perform these involuntary activities may also have different profiles than those who do not. For example, women active in transport may not be able to afford a vehicle, and those taking care of adults may have other financial burdens.55
These women may have different life circumstances, personal characteristics, and stressors that may cause depressive symptoms than those who do not perform these activities.
There is evidence that specific activity domains may be stressful or burdensome, which may explain why we saw such large increases in odds of depressive symptoms related to adult and child care and indoor household MVPA and overall nonelective MVPA. Performing housework and being a housewife have both been identified as risk factors for depression56,57
; performing housework has been found to be associated with increased perceived stress.58
A study of postpartum women found that women who took care of handicapped or ill relatives were four times more likely to have major depressive symptoms.59
A study of Swedish adults found that although the number of hours spent doing domestic work was not associated with anxiety or depression, participation in burdensome domestic work was associated with significantly increased odds of anxiety/depression.60
Our study's findings of increased odds of having elevated depressive symptoms with indoor household, adult and child care, and nonelective MVPA is supported by these other studies.
We also considered that change in MVPA could be associated with depressive symptoms. Mothers with elevated depressive symptoms at 12 months postpartum had higher MVPA levels at 3 months postpartum. It is possible that women with elevated depressive symptoms are more likely to experience declines in MVPA over the postpartum period, whereas mothers with low depressive symptoms experience stable or increasing MVPA levels. A decline in MVPA may be associated with an increase in depressive symptoms. Unfortunately, we do not present these estimates because of poor precision.
Limitations and strengths
The results of this study must be considered within the context of its limitations. First, a diagnosis of depression can only be make through clinical assessment. The EPDS is a self-report scale that assesses depressed mood and symptoms. However, performing clinical assessments on participants in population studies is costly and timely; therefore, depression screening tools frequently are used. The EPDS has been found to have satisfactory sensitivity and specificity and positive predictive value.7,32
The EPDS was designed with the purpose of identifying women who are depressed after childbirth and is a widely used screening tool for PPD.7,32,61
Physical activity measurement also relied on a self-report tool, which can create recall issues. However, as the assessment asked about the past week, problems with recall may be limited. The questionnaire asked women to consider the frequency, duration, and intensity of all forms of physical activity by domain, which may contribute to better recall. Self-report methods are frequently used to assess physical activity and have been determined to be an acceptable method to assess physical activity with a number of advantages.62
The physical activity questionnaire showed evidence of concurrent validity when compared to a structured diary and accelerometry and test-retest reliability.26
Another concern is that physical activity was assessed only during the past week; physical activity behavior can change from week to week, and the reported values may not be representative of usual behavior. This may be an important consideration for the early postpartum when women are likely developing new daily routines.
Precision was of concern in this study. The reporting of elevated depressive symptoms at 12 months postpartum was low in this sample (6%). Many women also reported no total or domain-specific MVPA, and the variation in levels of MVPA was low. This resulted in wide confidence intervals for the regression analysis.
There may be a concern of selection bias in our sample. The 688 women participating in the PIN Postpartum Study differed from the 480 eligible, nonparticipating women by being older, more educated, more affluent, more likely to be married, more likely to be white, of lower BMI at 3 months postpartum, and having lower depressive symptoms during pregnancy. There were no differences between participating women and those who were invited to participate in the study but declined. The rho for selection bias (the correlation between the error terms of the selection model and the final adjusted model) of the Heckman model was significant only for work MVPA; the estimates, once taking into account marital status and pregnancy depressive symptoms, changed by up to 63%. Therefore, we presented both the exact logistic regression and Heckman logistic regression estimates. Most conclusions made did not differ by model used, but there was large attenuation of the estimates of adult and child care and indoor household MVPA. Generalizability of the results may be an issue. Analysis using data from previous PIN cohorts also found that less educated, younger, African American, and parous women and women with higher pregnancy risk profiles were more likely to be underrepresented in the study.63,64
Despite these limitations, there are several strengths of this study. The prospective cohort design of the PIN Postpartum Study provided us with the opportunity to examine the association with physical activity early in the postpartum period with later depressive symptoms. There was a 9-month gap between assessments. This is beneficial for an investigation of depression, as it is a chronic condition and length of exposure might need to be considerable to have an impact. Data collection was extensive; a variety of factors related to the health of new mothers was assessed. This enabled us to control for a number of potential confounders. However, there is still the possibility of residual confounding. Although we examined many factors to determine if they confounded the association between physical activity and depressive symptoms, there are known (i.e., life events) and unknown factors that were not examined. Another strength is that both physical activity and depressive symptoms were assessed using reliable and valid assessment tools.7,26,32
The physical activity assessment was comprehensive, collecting data on duration, frequency, intensity, and domain. Previous studies of the association between physical activity and depressive symptoms among postpartum women have investigated only walking or recreational activity.