New mothers can reduce the risk of developing postnatal depression if they can find time to exercise for more than an hour every week, according to a new study. Exercising for at least 80 minutes each week could also help reduce symptoms among new mothers who have depression or anxiety, researchers found. But they should balance exercise with their recovery from childbirth, experts said. They could restart exercise with “gentle” walks, which they can do with their babies, and then increase to “moderate” activity when they are ready, they added. This moderate physical activity could include bri…