People who don't think life is worth living are more likely to die within the next few years, research from Japan shows.

The increased death risk was mainly due to cardiovascular disease and external causes — most commonly, suicide.

The research is the largest to date to investigate how 'ikigai', or "joy and a sense of well-being from being alive", affects mortality risk, and only the second to examine death from specific causes, according to Toshimasa Sone and colleagues from the Tohoku University Graduate School of Medicine in Sendai.

The investigators looked at 43,391 men and women 40 to 79 years old living in the Ohsaki region who were followed for seven years, during which time 3,048 died. All were asked, "Do you have ikigai in your life?" Fifty-nine per cent said yes, 36.4% said they weren't sure, and 4.6% said no.

Those who didn't have a sense of ikigai were less likely to be married or employed, and were also less educated, in worse health, more mentally stressed, and in more bodily pain. They were also more likely to have limited physical function.

But even after the researchers used statistical techniques to adjust for these factors, people with no sense of ikigai were still at increased risk of dying over the follow-up period compared to people who did have ikigai. The relationship also was independent of history of illness and alcohol use.

Overall, people with no sense of ikigai were 50% more likely to die from any cause during follow-up compared to those who did have a sense that life was worth living. They had a 60% greater risk of death from cardiovascular disease, most commonly stroke, and were 90% more likely to die of "external" causes. Of the 186 deaths due to external causes among study participants, 90 were suicides.

Another study released in August said that happiness could increase a person's life span by 7.5 to 9 years.

"Happiness does not heal, but happiness protects against falling ill," reported Ruut Veenhoven of Rotterdam's Erasmus University. The Dutch professor said the effects of happiness on longevity were "comparable to that of smoking or not".