A new Brigham Young University study adds our social relationships to the "short list" of factors that predict a person's odds of living or dying.

In the journal PLoS Medicine, BYU professors Julianne Holt-Lunstad and Timothy Smith report that social connections -- friends, family, neighbors or colleagues -- improve our odds of survival by 50 percent. Here is how low social interaction compares to more well-known risk factors:

Equivalent to smoking 15 cigarettes a day

Equivalent to being an alcoholic

More harmful than not exercising

Twice as harmful as obesity

"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 the PLoS Medicine editors in a summary of the BYU study and why it was done.

The researchers analyzed data from 148 previously published longitudinal studies that measured frequency of human interaction and tracked health outcomes for a period of seven and a half years on average. Because information on relationship quality was unavailable, the 50 percent increased odds of survival may underestimate the benefit of healthy relationships.

"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."

Holt-Lunstad said there are many pathways through which friends and family influence health for the better, ranging from a calming touch to 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 examining the data, Smith took a careful look at whether the results were driven primarily by people helping each other prolong their golden years.

"This effect is not isolated to older adults," Smith said. "Relationships provide a level of protection across all ages."

Smith said that modern conveniences and technology can lead some people to think that social networks aren't necessary.

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

Brad Layton worked on the study as an undergrad at BYU and appears as a co-author on the new study. Layton's involvement in this project helped him secure a spot as a Ph.D. candidate in the highly ranked epidemiology program at the University of North Carolina at Chapel Hill.