They say they act of frowning takes the use of more muscles than the act of smiling. Then they like to say, "Smile it takes less effort."
As an American I'm offended by "them." Just because I'm American doesn't mean I'm lazy and need to take the easy way out. I'm a worker I frown. Further, hasn't it been documented that exercise combats depression. Seems the only way to get happy is to use more exertion and work-out more muscles. So in the long run frowning is a better defense against depression than smiling.