How happy you are has no effect on how long you'll live, despite the widely held belief that unhappiness can lead to poor health.

"Illness makes you unhappy, but unhappiness itself doesn't make you ill," lead study author Dr. Bette Liu from Australia's University of New South Wales says. "We found no direct effect of unhappiness or stress on mortality, even in a 10-year study of a million women."

Adds study co-author Richard Peto, "Many still believe that stress or unhappiness can directly cause disease, but they are simply confusing cause and effect."

So, unhappiness and stress will not kill you. But picking a fight with the wrong person probably still will. Avoid self-destructive behaviors caused by unhappiness.

And why does nobody ever mention that one of the keys to living longer is hanging out with people that make you want to live longer? Avoid people who make you unhappy this Christmas. It's your life.