Single life has its charms and freedoms, but adults who never marry may not live as long as their wedded peers, new research suggests.

While the protective effect of marriage on health and longevity has been pointed out before, newer research is zeroing in on the never-married folks. Staying single all your life may not be good for your health or your lifespan, according to researchers at the University of California, Los Angeles.

The team looked at the 1997 U.S. National Death Index and the 1989 National Health Interview Survey. In 1989, almost half of the survey sample was married; about 10 percent widowed; 12 percent divorced; 3 percent separated; 5 percent living with someone; and 20 percent had never married.

Compared with married people, those who had never been married were 58 percent more likely to have died at the end of the study's eight-year follow up period.

By comparison, those who were widowed were nearly 40 percent more likely to die during the follow-up than were married participants, while those who had been divorced or separated were 27 percent more likely to die.

Still, the UCLA researchers, who published the study in the Journal of Epidemiology and Community Health, said the findings can't prove cause and effect.

And other researchers say it could be a chicken-and-egg question. Does single status lead to lack of health, or "are they single because they are unhealthy?" asked Patrick Markey, an assistant professor of psychology at Villanova (Pa.) University. He and his wife, Charlotte Markey, a researcher at Rutgers University in New Jersey, have studied the topic of marriage's effects on health.

"Marriage, at least for males, has a huge benefit" on health, said Patrick Markey. He and his wife looked at more than 2,200 adults, all participants in the New Jersey Family Health Survey, and found that being married was associated with men being more "health proactive" - or practicing good health habits, such as seeing the doctor regularly for check-ups.

"Marriage helps men out more than women," Markey said, citing more results from the study, which was published in the journal Sex Roles in 2005. Married women and single women both tend to be "health proactive," the researchers found.

"I guess the (married) women may be reminding the men" about good health practices, Markey said.

So why do unmarried women stay healthy? "Single women tend to have good social networks," Markey said. They have people to turn to when they need help, he said, and typically more so than single men.

But another researcher, Howard S. Friedman, a professor of psychology at the University of California, Riverside, said singles shouldn't necessarily expect a lack of wedding vows to shorten their lives.

"We did not find that singles are at greater risk for premature mortality," he said, citing his long-running research on predictors of health and longevity.

"We found, confirming most other research, that married men live longer — that is, are at less risk of premature mortality — than divorced men, but this was not primarily due to any protective effects of the marriage itself," he said.

"Rather, it seems both that some men are at greater risk for poor marriages and poor health, and that poor marriages, breakups and divorces are stressful," Friedman said.

Friedman's research also links childhood personality, especially conscientiousness and not experiencing a parental divorce, as predictive of longevity.