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 people with strong personal relationships are 50% more likely than others to survive over a specific period of time.

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 308,849 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.

The 50% number held up even when researchers adjusted their figures for factors such as age and health status.

Holt-Lunstad said the study researchers didn't calculate how much longer those with the relationships lived, nor what percentage of them died during the study periods.

But it did appear 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, she 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."