Happy people may not only enjoy life more, but new research suggests they also have more life to enjoy.

Almost 4,000 people, enrolled in a long-term aging study in Britain, were asked to score how they were feeling on a particular day.

"We used quite simple measures," says Andrew Steptoe of University College London. "So the 'positive affect' measure was a combination of how happy people were feeling, how excited they were feeling, how content they were. And these were all rated on a simple scale, a five-point scale, from 'not at all' to 'extremely.'

Over the next five years, the researchers noted deaths among study participants.

"What we found is that the people with higher positive affect - so if you like, the happiest people - were at reduced risk of dying over this period."

The happiest people, in fact, had a 35 percent lower risk of death than the least happy.

In contrast to previous studies, in this research the people were asked how they felt at that moment. Previous studies usually asked questions like, 'how have you felt over the past week?' But Steptoe says psychologists have shown that people are not good at answering that type of question.

"For example, if their favorite football team lost the previous weekend or something like that, they would rate themselves less happy over the whole week, even though it might not actually have affected them in that way. So, getting at how people are feeling at the time overcomes that sort of problem."

At the same time the study participants answered questions about how they were feeling, they also gave a saliva sample. Researchers plan to test those samples for the presence of the stress hormone cortisol to see if there's also a link between stress and longevity.