Teens who say they think it's unlikely that they'll live to age 35 are more likely to engage in risky behaviors such as abusing drugs or attempting suicide, according to a new study.

In 1994 and 1995, researchers surveyed 19,000 teenagers and found that one in seven said they had a 50-50 chance, or less, of living to age 35. When the researchers caught up with the participants 14 years later, they found that those who still said they weren't likely to live to 35 were three times more likely to have attempted suicide, compared with their peers who were more optimistic about their survival.

Because of the strong association with suicide, researchers suggested that "monitoring survival expectations may be useful for identifying at-risk youth," the researchers wrote.

Participants in the study completed surveys about their habits and perceptions of longevity at ages 13 or 14, one year later, seven years later and 14 years later. (About 15,000 participants responded at the time of the last survey.)

The researchers found that those who reported feeling that they would not likely live past 35 at each survey point were increasingly likely to participate in such unhealthy behaviors as using drugs or smoking heavily.

"Perceptions of immortality and invincibility have been offered as explanations for heightened risk-taking among youth," the researchers wrote. "However, fatalism and perceived vulnerability may also encourage greater recklessness."

Among those who said they had a low likelihood of surviving to 35 both in high school and seven years later, 14 percent had thought about suicide ,  and 5 percent had attempted it. Among those who said they believed they would live past 35, 6 percent reported having suicidal thoughts, and 1.1 percent said they had attempted suicide.

Additionally, the researchers found that those who had reported feeling, even at only one point, that they were not likely to live to 35 were more likely to engage in dangerous behaviors, compared with those who reported unwavering confidence in surviving beyond that age.

Not believing that one will live past 35 is a form of hopelessness, and "we know that hopelessness is a significant factor associated with thoughts of suicide, suicide attempts and death by suicide," said Dr. Tim Lineberry, a psychologist and suicide expert at the Mayo Clinic. Lineberry was not involved with the study.

He added that he might start asking his patients if they believe they will live past 35 as an entry point to discussing their level of hopelessness.

In comparison with their more-optimistic peers, those who said in high school and seven years later that they thought they would die before 35 were nearly twice as likely to binge drink, two-and-a-half times as likely to smoke a pack of cigarettes a day, and nearly four times as likely to use illegal drugs (aside from marijuana) on a weekly basis.

Substance abuse itself has been associated with a higher rate of suicide, the researchers noted. 

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