Mike Johnston has no idea what he was thinking when he took up cigarettes at age 15.
"I was definitely more impulsive back then than I am now," said Johnston, 39, of Oakville, Mo., as he puffed away on a downtown sidewalk during a work break. "I was young and had no responsibilities. Now I have a wife and two kids."
Charlie Condor, 49, of St. John, Mo., was smoking with co-workers when he admitted that his lifestyle and woeful views about life might have played a role in his decision to start smoking 28 years ago.
"Just kid stuff, you know? I was coming up through adulthood and it seemed like life was against me," he said.
The way that Johnston and Condor assess their younger selves mirrors recent findings of two researchers at University of Missouri.
By analyzing data collected during a long-term study, Andrew K. Littlefield, doctoral student in psychology, and Kenneth J. Sher, professor of psychology, have found that people who smoke at age 18 have higher rates of impulsivity than non-smokers at that age. They've also found that those who quit between ages 18 and 25 show the biggest decreases in impulsivity during that time period.
The study, which began in 1987 with one group of 489 Mizzou students and has continued with several more groups, is intended to assess substance use in general, not just smoking, according to Littlefield.
Among other things, subjects are asked to rate how well two statements describe their behaviors on a scale of one to 10. The statements pertain to whether they tend to think through facts, details and consequences before deciding to do something and whether they tend to worry a lot.
They are surveyed seven times - once a year during college then at about age 25, 29 and 35.
"We see the biggest changes in impulsivity and neuroticism between age 18 and 25," Littlefield said. "After age 30, most personality traits are usually set in plaster and they're not changing much."
Changes in people ages 18 to 25 begin happening when they leave their families, go to college, enter the workforce, get married and have children. Logic would dictate that becoming less impulsive and neurotic are a part of maturing, which causes many smokers to quit.
But Littlefield and other scientists aren't ready to draw that conclusion yet.
Quitting smoking might be prompting the changes in personality traits, he said. He stressed, however, that he means personality changes over a long time frame, not short-term ones like nervousness and lower self-regulation that come from nicotine withdrawals.
Littlefield and Sher have also concluded that, by the time a person is 35, smoking is usually no longer related to neuroticism and impulsivity.
"Now, it's moving from those traits to addiction and compulsivity, which is when your behaviors are patterns," Littlefield said. "You're on autopilot, lighting up without thinking when you get out of bed or on the way to work."
He believes the findings of his study could be useful in figuring out ways to help people quit smoking before it becomes addictive and compulsive.
Studies have shown, he said, that "there are residual effects when you follow up with students after they've taken a money management course. You find that many of them reduce drinking and either quit or reduce smoking. They not only spend less, but they reduce behaviors associated with high impulsivity."
He urges people to think of self-regulation as a muscle. It can become fatigued if you use it too much, or it can grow stronger when exercised.
"Likewise," he added, "if you can target internal thoughts you can make them more positive and reduce the impact of being neurotic."