Researchers have found a surprising correlation between longevity and religious faith.

Church-goers appear to live up to four years longer than atheists, at least according to an analysis of 1,000 obituaries published across the United States.

The Ohio State psychology researchers behind the study insist there is merit to the connection: people with religious affiliations often volunteer and engage in social activities throughout their lives - something routinely tied to longer lifespan.

But they found that this socializing only appeared to boost longevity by a year at most - suggesting other elements of religious life, such as low alcohol intake, could contribute.

The Ohio State University study was based on 1,000 obituaries published across the US in 2011. While the data set is small, the psychology research team insisted there is merit to the correlation

'There's still a lot of the benefit of religious affiliation that this can't explain,' study lead author Laura Wallace, a doctoral student in psychology at The Ohio State University.

Dr Baldwin Way, associate professor of psychology at Ohio State who co-authored the study, concurred.

He said that, while the findings may sound like tosh to atheists, there was a correlation they couldn't ignore.

'The study provides persuasive evidence that there is a relationship between religious participation and how long a person lives,' he said.

Dr Way surmises that this correlation might depend on how religious one's community is.

Indeed, the first installment of this study involved 505 obituaries published in the Des Moines Register in Iowa in January and February 2012.

There, the lifespan gap was even greater: religious people lived 9.45 years longer than their atheist peers - but that shrunk to 6.48 years when they took gender and marital status into account .

The second study included 1,096 obituaries from 42 major cities in the US published on newspaper websites between August 2010 and August 2011.

In this study, people whose obits mentioned a religious affiliation lived an average of 5.64 years longer than those whose obits did not, which shrunk to 3.82 years after gender and marital status were considered.

Many studies have shown that people who volunteer and participate in social groups tend to live longer than others.

The researchers combined figures from both studies to see if the volunteer and social opportunities that religious groups offer might explain the longevity boost.

Results showed that was only part of the reason why religious people lived longer, according to the researchers.

Wallace said: 'We found that volunteerism and involvement in social organisations only accounted for a little less than one year of the longevity boost that religious affiliation provided.'

Dr Way said the reason for their longevity may be related to the rules and norms of many religions that restrict unhealthy practices such as alcohol and drug use and having sex with many partners.

He said many religions also 'promote stress-reducing practices that may improve health, such as gratitude, prayer or meditation.'

The fact that the researchers had figures from other cities also allowed them to investigate whether the level of religiosity in a city and a city's 'personality' could affect how religious affiliation influenced longevity.

The findings showed that a key personality element related to longevity in each city was the importance placed on conformity to community values and norms.

In highly religious cities where conformity was important, religious people tended to live longer than non-religious people.

But in some cities there is a spillover effect.

Wallace added: 'The positive health effects of religion spill over to the non-religious in some specific situations.

'The spillover effect only occurs in highly religious cities that aren't too concerned about everyone conforming to the same norms. In those areas, non-religious people tend to live as long as do religious people.'

Dr Way said there are limitations to the study, including the fact that it could not control for important factors related to longevity such as race and lifestyle.

But a potential strength was that, unlike other studies, religious affiliation was not self-reported, but was reported by the obituary writer.

But Wallace said that the findings, published today by the journal Social Psychological and Personality Science, provided additional support to the growing number of studies showing that religion does have a positive effect on health.