People who live longest tend to be those who look on the bright side of life, research has shown.
Scientists in the US who studied 243 centenarians found that, far from being mean-spirited and world weary, most were cheerful, outgoing and sociable.
The positive personality traits may in part be genetically based, the researchers believe.
The study was part of the Longevity Genes Project investigating more than 500 Ashkenazi Jews over the age of 95, and 700 of their offspring.
Ashkenazi Jews, from eastern Europe, are good candidates for gene studies because they are genetically similar.
Lead scientist Nir Barzilai, director of the Albert Einstein College of Medicine's Institute for Aging Research in New York, said: "When I started working with centenarians, I thought we'd find that they survived so long in part because they were mean and ornery. But when we assessed the personalities of these 243 centenarians, we found qualities that clearly reflect a positive attitude towards life.
"Most were outgoing, optimistic and easygoing. They considered laughter an important part of life and had a large social network. They expressed emotions openly rather than bottling them up."
Tests showed that the study group, who had an average age of 97.6 and were three-quarters women, had lower "neurotic personality" scores than a representative sample of the general population. They also had higher scores for being conscientious.
The findings were published in the latest online edition of the journal Aging.
Dr Barzilai added: "Some evidence indicates that personality can change between the ages of 70 and 100, so we don't know whether our centenarians have maintained their personality traits across their entire lifespans.
"Nevertheless, our findings suggest that centenarians share particular personality traits and that genetically based aspects of personality may play an important role in achieving both good health and exceptional longevity."
Previous research on longevity has focused on physiological advantages that may help people live longer, such as naturally high levels of high density lipoprotein (HDL) or "good" cholesterol.
Boosts Immune System
Laughter not only makes you feel good, but it helps boost your immune system too. The Department of Clinical Immunology at <a href="http://www.llu.edu/medicine/index.page" target="_hplink">Loma Linda University School of Medicine</a>, found that laughter decreases serum cortisol levels (stress chemicals), increases T lymphocytes (white blood cells that play a key role in immunity), and increases the number of natural killer cells. These results suggest that laughter stimulates the immune system and ultimately makes you healthier.
A study by a Canadian University found that laughter makes you more attractive to the opposite sex. The study found that smiley people seem more approachable, plus when you laugh, your blood supply increases, causing a rosy glow to the skin, making it appear more youthful and appealing to look at.
Provides Pain Relief
Researchers at <a href="http://www.ox.ac.uk/" target="_hplink">Oxford University</a> found that laughter can act as an effective pain reliever. Laughter release the feel-good chemical endorphin and it acted like pain relief to the participants. The study also found that chuckling helped increased pain threshold.
Helps Keep Heart Healthy
According to a recent study by cardiologists at the <a href="http://www.umm.edu/" target="_hplink">University of Maryland Medical Center</a> in Baltimore, laughter, along with an active sense of humor, could help protect you against a heart attack. The study found that people with heart disease were 40% less likely to laugh in a variety of situations compared to people of the same age without heart disease. Another study by Dr. William Fry, associate professor of clinical psychiatry at <a href="http://www.stanford.edu/" target="_hplink">Stanford University</a>, compared laughter to "inner jogging," and claimed that laughing 100 times a day is the equivalent of 10 minutes of rowing. The study also found that laughter increases the heart rate, improves blood circulation, and works muscles all over the body.
Keeps You Fit
A study by<a href="http://www.llu.edu/" target="_hplink"> Loma Linda University</a>found that ''mirthful laughter'' reduces the stress hormones cortisol and catecholamines, much the same way that moderate physical exercise does. They also found that a good belly laugh positively effected two hormones that regulate appetite, leptin and ghrelin, meaning it could also help decrease appetite.