Giving birth and having a new infant is a major life change, and it's not uncommon for new mothers to feel anxious and depressed. But when postpartum depression and anxiety mean that new mothers find it difficult to care for themselves and care for and bond with their babies, it can interfere with their child's cognitive, social and emotional development.

Postpartum anxiety and depression are usually treated with medication and counseling. Unfortunately, these are often associated with side effects, poor adherence, a lack of access and expense.

It helps to start early. Beginning to exercise within three months of giving birth reduced depressive symptoms more than beginning to exercise within the first 12 months.

Physical activity has been shown to ease anxiety and depression symptoms at minimal cost in non-pregnant populations. Few studies, however, have looked at the effect of exercise on postpartum anxiety and depression.

When Canadian researchers undertook a systematic analysis that compared interventions that included exercise to those that did not, they found exercise was associated with less severe symptoms of postpartum anxiety and depression. Exercise also reduced the risk of major postpartum depression by 45 percent.

The findings mean that exercise could provide new mothers with an inexpensive, relatively safe and easily accessible alternative to improve their mental health. “It was great to see that exercise was beneficial in the postpartum period,” Margie Davenport, corresponding author on the study, told TheDoctor in an email.

Persistent sadness and feelings of emptiness, excessive fatigue and loss of interest in activities that one previously enjoyed are common signs of postpartum depression, she explained. “Anyone who thinks she may be experiencing postpartum depression should speak to her doctor,” said Davenport, a professor of kinesiology, sport and recreation at the University of Alberta.

Data from over 4,070 participants in 35 studies from 14 countries were included in the meta-analysis. The studies charted the effectiveness of various interventions, including no intervention; education about postpartum depression alone; standard postpartum care with exercise to treat anxiety and depression beginning within 12 weeks of giving birth; or standard postpartum care with exercise within the first 12 months.

More exercise led to a greater reduction in symptoms. The minimum threshold for achieving a modest reduction in symptoms was 80 minutes of moderate intensity exercise, such as brisk walking for 20 at least four times a week.

Participants in the exercise conditions exercised between one and five days a week. They did aerobics, strength training, stretching, yoga or combinations of these. Each exercise session lasted between 15 and 90 minutes.

Beginning to do any form of exercise within the first three months of giving birth reduced depressive symptoms more than beginning to exercise within the first 12 months. The amount of exercise was directly associated with its effect on depressive symptoms: more exercise led to a greater reduction in symptoms. The minimum threshold for achieving a modest reduction in symptoms was 80 minutes of moderate intensity exercise, such as brisk walking at least four times a week.

Additional rigorous studies are needed to support these findings, the researchers said. And future studies could examine the effects of exercise on depression and anxiety in women who experienced complications such as preeclampsia, that may have resulted in exercise restrictions during pregnancy.

The study is published in the British Journal of Sports Medicine.