Regular physical activity lasting 45 minutes three to five times a week can reduce poor mental health - but doing more than that is not always beneficial, a large US study suggests. A total of 1.2 million people reported their activity levels for a month and rated their mental wellbeing. People who exercised had 1.5 fewer "bad days" a month than non-exercisers, the study found. Team sports, cycling and aerobics had the greatest positive impact.(BBC News)