London: The idea that overweight people can lose weight by being optimistic has been quashed by research. New evidence has emerged to suggest that certain characteristics may influence one's health; for example, optimists are more likely to be overweight.

Dr Martin Hagger, a health psychologist at the University of Nottingham and Curtin University, Australia, said personalities are a result of both genes and the environment.

"Knowing you fall into one specific camp doesn't immediately mean you're going to develop heart disease, for instance, but it should wake you up to the risk and, as a result, give you the opportunity to recognize and target the less healthy aspects of your character ” such as smoking or drinking," the Daily Mail quoted him as saying.

Researchers from Doshisha University in Kyoto, Japan, and other centres, assessed obese men and women undergoing a six-month weight-loss programme involving counseling, nutrition and exercise.

The researchers found that those who were most positive lost the least weight. It's thought that looking on the bright side led to patients not caring about their weight problem and always giving into temptation.

A major University of California study found their confidence about their ability to defeat life's difficulties and willingness; therefore, to take more risks might explain why happy types are also more likely to die young.

Psychologist Dr Howard S. Friedman analysed data on more than 1,500 children from the age of ten and followed them into adulthood.

"Those who had the best sense of humour as kids lived shorter lives, on average, than those who were less cheerful," he said.

Another study at Stanford University found that most cheerful kids grew up to smoke, drink more and have riskier hobbies.