EACH OF US carries a single gene which helps determine how happy we are with our lives, according to a new study.

The gene, known as 5-HTT, has a significant effect on how cheerful we feel depending on which variant is held in our DNA. It helps cells in our brains recycle serotonin – the same chemical affected by many prescribed antidepressants – and comes in long and short forms. The long variety are more effective at helping to transport the chemical.

People who inherit two long forms of the gene – one from each parent – are 17 per cent more likely to report being “very satisfied” with life than those with two short forms, while people with one of each are halfway in between, the research showed.

Some 26 per cent of those with two short genes said they were “very dissatisfied” with life, against 20 per cent of those with two long.

“It’s the first formal finding of a happiness gene, although I’m sure others will be found,” study author Jan-Emmanuel De Neve, of the London School of Economics, told the New Scientist, adding: “The more efficient version appears to influence predisposition towards happiness.”

Unfortunately, total contentment isn’t a done deal no matter what your DNA says. “Our well-being isn’t determined by this one gene,” De Neve told The Guardian. “Other genes and especially experience throughout the course of life will continue to explain the majority of variation in individual happiness.

“But this finding helps to explain why we each have a unique baseline level of happiness and why some people tend to be naturally happier than others, and that’s in no small part due to our individual genetic make-up.”

The study, which was first published in the Journal of Human Genetics, looked at 2574 adolescents in the US.