Having great friends, a strong marriage and children who love you may be just as important to living a long life as something like quitting smoking, a new study finds.

Researchers from Brigham Young University have found that people who have lots of close relationships have better odds of living a long life than those who are lonely.

The study, which appears in the July issue of PLoS Medicine, found that strong social connections improve our odds of survival by 50 per cent. In fact, the protective effect of strong social relationships exceeds the influence of other early-death risk factors, such as:

• not exercising
• obesity

Low social interaction, on the other hand, is equivalent to:

• smoking 15 cigarettes a day
• being an alcoholic

"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," write PLoS Medicine editors in a summary of the study.

To reach their findings, BYU psychology professor Julianne Holt-Lunstad and counseling psychology professor Timothy Smith analyzed data from 148 previously studies. All were longitudinal studies that measured frequency of human interaction. Together, these studies included 308,849 people who were followed for about 7.5 years, on average.

Holt-Lunstad says there are lots of ways that friends and family can influence health for the better, ranging from the comfort provided by physical contact and providing finding meaning in life.

"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," Holt-Lunstad said in a news release.

Smith said with modern conveniences and technologies, many people might underestimate the value of face-to-face contact.

"We take relationships for granted as humans -- we're like fish that don't notice the water," Smith said in the release. "That constant interaction is not only beneficial psychologically but directly to our physical health."

Holt-Lunstad notes that information on relationship quality was unavailable from most of the studies they examined.

"The data simply show whether they were integrated in a social network," Holt-Lunstad said. "That means the effects of negative relationships are lumped in there with the positive ones. They are all averaged together."

She added that the study method also made it difficult to define which type of relationships is most protective: family or friends. But she says the 50 per cent increased odds of survival may actually underestimate the benefit of healthy relationships.

The authors suggest that policymakers should consider ways to help people maintain social relationships as a way of keeping the population healthy.

"Physicians, health professionals, educators, and the public media take risk factors such as smoking, diet, and exercise seriously; the data presented here make a compelling case for social relationship factors to be added to that list," they write.