There's a factor to happiness....

The Happiness Factor

By Nancy Kalish

Scientists know that positive people are happier, period. Tapping into your bright side is easier than you'd guess.

Joie de vivre. We all know people whose engagement with life can only be described as joyful. Fittingly, nature rewards these happy-go-lucky types: Being optimistic in middle age increases life span by at least 7.5 years--even after accounting for age, gender, socioeconomic status, and physical health, according to a large Yale University survey. What's behind their hardiness: They minimize the destructive effects of stress. "Of course, optimists get stressed," says David Snowdon, a professor of neurology at the University of Kentucky who studies aging. "But they automatically turn the response off much more quickly and return to a positive mental and physical state." Here are four habits that longevity experts say are at the heart of a sunny disposition--and that you can adopt, too.