Researchers found that a group of subjects who reported high happiness levels had a 35 percent reduced risk of dying five years later

It's no secret that social factors, like having a good support system in place around you, are linked to longevity. A related factor, being happier throughout life, has also been associated with reduced risk of death. The problem with the happiness-longevity relationship is that most studies have asked patients to rate their happiness looking back over their lives. This can lead to bias, since people's memories can be unreliable: People may report greater happiness in retrospect than they actually experienced at the time, or the opposite could be true.

The team that headed a new study addressed this issue by asking people about their happiness and stress levels just four times throughout the course of a single day. Then, they kept track of the participants for the next five years, and found that the people who reported the highest happiness levels had a 35 percent reduced risk of dying, compared to the unhappiest people. This was true even after the researchers controlled for a range of other variables that could have affected the relationship, like depression, age, health behaviors, various diseases, and gender.

Brain studies have found that positive emotional states are linked to activation in areas of the brain that govern certain body processes, hormones, and inflammation, which could well play a role in death risk. But, as the authors point out, it's also possible that positive mood or happiness measured at one point in time could itself reflect "underlying biological processes, or unmeasured behavioral or temperamental factors that are responsible for the survival effects."