A little bad luck can be good for us.

That's the surprising result of a new national, multi-year study of nearly 2,400 people that found that, basically, what doesn't kill us can make us mentally stronger.

The study, by researchers at the University at Buffalo and the University of California, Irvine, found that people who encountered some misfortune in their life emerged more resilient and adaptable than either those who had nothing bad happen to them or those with a long history of adversity.

"I think this study has an encouraging message for older Americans," says author Mark Seery, assistant professor of psychology at the University at Buffalo. "Just because people have experienced difficulties or even something terrible in the past does not mean that they are doomed to be forever damaged. In fact, they may have ended up being stronger now because of the experience."

Mindy Fain, M.D., codirector of the Arizona Center on Aging, also sees a positive message in the study's findings. "Those who experience some adversity have the opportunity to learn from it [and] are better positioned to successfully deal with some of the challenges of growing older," she says.

The study participants ranged in age from 18 to 101. Between 2001 and 2004, they were asked about the lifetime crises they had experienced, based on 37 categories of traumatic events, including the death of a loved one, becoming seriously ill or injured, experiencing a natural disaster and going through a divorce. Participants were also asked about their mental health and sense of well-being, including any posttraumatic stress symptoms, functional impairment or distress.

Researchers then totaled the number of events that people had experienced and examined the relationship between the number of events and the various measures of participants' mental health.

The results showed that people with a history of some lifetime adversity were less negatively affected by recent crises when compared with those with no or high adversity.

"In our sample, people who experienced between around two and four or five events tended to report the best mental and physical health outcomes," Seery wrote in an e-mail.

The researchers theorized that dealing with some difficult challenges help people learn coping skills, as well as build confidence that they could overcome hard times.

However, Seery cautioned against thinking that there are an "optimal" number of disasters that people can tolerate. Instead, people should realize that "being sheltered from adversity may protect us in the short term, but does not contribute to strengthening us later."

At the other extreme, the study suggests that being exposed to a long run of adversity can also overwhelm a person and lead to declining mental health.

The study found no evidence that certain categories of events (such as the death of a loved one) had more of an effect on mental health than others, Seery noted.

And age wasn't a factor either. Although researchers had wondered whether those with a low number of lifetime traumas might simply be younger and more resilient — and, conversely, that older people would have experienced more troubles during their longer lives — the evidence proved otherwise. The number of disasters a person had to overcome, regardless of age, was a better predictor of that person's mental health.

While this doesn't mean people should go looking for bad experiences to help toughen them up, those who have overcome hardship should feel encouraged. As Ernest Hemingway wrote in the novel A Farewell to Arms, "The world breaks everyone and afterward many are strong at the broken places."

Candy Sagon writes about health and nutrition for the AARP Bulletin.