A new study from the US suggests that social interaction should be considered an important factor for extending lifespan, on a par with other health and lifestyle factors, to the extent that low social interaction harms longevity as much as alcoholism and smoking, has more impact than lack of exercise, and is twice as harmful as obesity.

Researchers at Brigham Young University (BYU) in Provo, Utah, conducted a meta-analysis of published studies and found that having social ties with friends, family, neighbours and colleagues can improve our odds of survival by 50 per cent. You can read about their study online in a paper published in the July issue of PLoS Medicine.

"The idea that a lack of social relationships is a risk factor for death is still not widely recognized by health organizations and the public," noted the journal editors in their summary.

First author Dr Julianne Holt-Lunstad, a professor in the Department of Psychology at BYU, and co-authors Dr Timothy Smith, a professor of Counseling Psychology at BYU, and Brad Layton, formerly of BYU and now working towards a PhD in epidemiology at the University of North Carolina at Chapel Hill, suggest that social relationships should be added to the shortlist of factors that impact a person's odds of living or dying.

For their analysis, they pooled data from 148 published longitudinal studies (the sort that track groups of people over time, taking observations now and again), and found that low social interaction had a similar impact on lifespan as being an alcoholic or smoking 15 cigarettes a day. It was also more harmful than physical inactivity, and twice as harmful as obesity, they suggested.

The studies they examined measured the frequency of human interaction and tracked a range of health outcomes for an overall average period of 7.5 years. If the studies had also yielded data on quality of relationships, the authors suggest the impact of healthy social interaction on odds of survival could be higher than 50 per cent.

To work out the impact statistically, Holt-Lunstad and colleagues extracted an "effect size" from each study: this quantifies the difference between two groups, in this case, the likelihood of death between groups that differed in terms of their social ties.

Using a statistical method known as "random effects modeling" they then worked out the average effect size as an odds ratio (OR), which essentially expresses the chance of something happening (in this case death) in one group with the chance of it happening in another group, as a ratio.

Holt-Lunstad told the press that the data they analyzed only showed whether the participants were "integrated in a social network"; there wasn't enough detail to enable them to separately examine the negative and positive effects of being in the network, "they are all averaged together," she added.

They found that the average OR for these 148 studies was 1.5, that is people with stronger social ties had a 50 per cent higher chance of survival than those with weaker ones.

The researchers discovered another important result: studies that considered simple measures such as marital status were less predictive of risk of death than those that took into account more complex measures of social integration.

Family, friends, and colleagues influence our health for the better in lots of small as well a big ways, said Holt-Lunstad, so that:

"When someone is connected to a group and feels responsibility for other people, that sense of purpose and meaning translates to taking better care of themselves and taking fewer risks."

The researchers also studied the results to see if the effect on longevity was coming mainly from people supporting each other later on in life, but this was not the case, the effect was spread out over age:

"This effect is not isolated to older adults," said Smith.

"Relationships provide a level of protection across all ages," he explained.

Humans are social animals, yet in developed nations many people no longer live in extended families, living apart from each other, with relatives at the other end of the country or on the other side of the world. There is also a growing trend to delay having children, and an increasing number of people living alone.

A recent survey by the UK's Mental Health Foundation found that one in ten adults often feels lonely, one in three has a close friend or relative whom they believe to be very lonely, and half think that generally, people are getting lonelier.

Similarly in the US, there has been a three-fold increase in the last twenty years in the number of Americans who say they have no one to confide in.

All this adds up to an increase in social isolation, which many experts believe is bad for human health. Although further research is needed to support its findings, it would seem that this study confirms that view, and calls for more attention to be paid to social factors, in the assessment of risks to health and life, and in interventions to modify them.

It doesn't matter how much we rely on modern conveniences and technology, we still need social networks, not just for our mental but also our physical health, said Smith.

"We take relationships for granted as humans -- we're like fish that don't notice the water," he added.

"Social Relationships and Mortality Risk: A Meta-analytic Review."
Julianne Holt-Lunstad, Timothy B. Smith, J. Bradley Layton.
PLoS Medicine, 7(7): e1000316; July 2010.
DOI:10.1371/journal.pmed.1000316

Additional source: PLoS Medicine Editors' Summary.

Written by: Catharine Paddock, PhD