LOS ANGELES — Don't despair if you can't fit in the recommended 30 minutes of daily exercise. Growing evidence suggests that even half that much can help.

It's still no excuse to slack off. Regular exercise strengthens muscles, reduces the risk of some diseases and promotes mental well-being. The more exercise, the better.

But not everyone has the time or willpower. So researchers set out to find the minimum amount of physical activity needed to reap health benefits. The findings by a study in Taiwan suggest just 15 minutes of moderate exercise a day can lead to a longer life.