There is "clear and compelling evidence" that happier people are healthier and live longer than their sad-sack counterparts, according to a review of more than 160 studies.
"I was almost shocked, and certainly surprised, to see the consistency of the data," Ed Diener, the University of Illinois psychology professor emeritus who lead the review, told Reuters.
The review, published Tuesday in the journal Applied Psychology: Health and Well-Being, examined eight different types of studies and experimental trials of both humans and animals that have looked at the connection between a positive outlook and overall health and longevity.
One study of 5,000 university students that was carried out over 40 years found that the more pessimistic people in the study tended to die younger than those who looked on the sunny side.
Others found that animals living in stressful conditions had weaker immune systems and died at a younger age than animals that lived without those stressors.
Yet, as strong as the connection may be between happiness and health and longevity, "There is still no direct proof that happiness boosts longevity in and of itself," the Reuters report noted.
Prof. Diener, however, is so convinced of the positive impact of happiness that he thinks it should be right up there with public-health messages concerning exercise and smoking.
"It may be time to add 'Be happy and avoid chronic anger and depression' to the list," he said.