People who live over 100 years tend to see the sunny side of life, according to new research.

A study of 243 centenarians revealed that most were cheerful and sociable. The positive personality traits may be genetically based, the researchers believe.

The study involved Ashkenazi Jews from eastern Europe. They are good candidates for gene studies because they're genetically similar to one another. Tests showed that the study group had lower "neurotic personality" scores than a representative sample of the general population. They also had higher scores for being conscientious, said Nir Barzilai, of the Albert Einstein College of Medicine's Institute for Ageing Research in New York.

"Most were outgoing, optimistic and easygoing," he said.

"They considered laughter an important part of life and had a large social network. They expressed emotions openly rather than bottling them up."