TUESDAY, July 27 (HealthDay News) -- Family and friends may do more than provide companionship: They also may boost your longevity, making as much of a difference as not smoking, a new analysis of studies suggests.
Researchers combined the results of 148 studies and estimated that adults with strong personal relationships may live an average of almost 4 years longer than those with weaker social ties.
The analysis doesn't prove that relationships directly help people live longer, but it seems clear that "our relationships come with more than just emotional benefits," said study author Julianne Holt-Lunstad, an associate professor of psychology at Brigham Young University.
"They can influence our longevity and our health," she added.
The study is published in the July issue of PLoS medicine.
Holt-Lunstad and colleagues examined studies involving almost 309,000 people on the effects of relationships -- such as those with friends, family, roommates and spouses -- on life span. The studies, conducted in North America, Europe, Asia and Australia, followed people for an average of 7.5 years.
"Among adults over age 18, those with strong social relationships are likely to live an average of 3.7 years longer than those with weaker social relationships," said study co-author Timothy Smith, a psychology professor at Brigham Young University.
The effect held up even when researchers adjusted their figures for factors such as age and health status.
It appears that strong relationships had an effect comparable to that of quitting smoking and a greater effect than known risk factors such as obesity and alcohol abuse, Holt-Lunstad said.
The challenge now is to put this information to good use, said the authors, who noted that in this era of technology, the quantity and quality of relationships seems to be decreasing.
Sonja Lyubomirsky, a psychology professor who studies happiness at the University of California at Riverside, said friends and family can affect your health in a variety of ways. "They help support good health habits: They remind us to put that seat belt on and ask us about that pain we've had, have we had that checked out? That may be the biggest factor."
Relationships may also reduce stress and boost the immune system, she said.
Or, it could be that people with more relationships live longer because "they're healthier to begin with: They could be more active and have more energy to engage in social activities," she said.
But other factors may also play a role, and it may be impossible to ever definitively say that more social relationships translate to longer lifespans, she said.
When scientists want to know if one thing causes another, they often turn to the gold standard of research: They randomly assign people to groups -- maybe one gets a medication and one doesn't -- and see what happens.
But, "you can never do a experiment where you isolate 100 people and then take 100 people and give them lots of friends," she said.
The U.S. National Library of Medicine has details on stress.
SOURCES: Julianne Holt-Lunstad, associate professor, psychology, and Timothy Smith, PhD, professor, psychology, both of Brigham Young University, Provo, Utah; Sonja Lyubomirsky, Ph.D., psychology professor, University of California, Riverside; July 2010 PLoS Medicine
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