The odds that adolescents will smoke, drink or use marijuana may have a lot to do with their physical development, regardless of their school grade level or how old they are, a new study shows.

Researchers found that among more than 5,700 10- to 15-year-olds in the U.S. and Australia, those who were in late-stage puberty were more than three times as likely as those in early-stage puberty to say they regularly smoked, drank or used marijuana.

In fact, it was the “biologically driven process of puberty” that showed the strongest influence over the adolescents’ substance use, according to the study’s lead author, Dr. George C. Patton of the University of Melbourne in Australia.

In contrast, he told Reuters Health, a child’s age or grade in school had no effect on smoking, drinking and drug use.

Past studies have shown that children who enter puberty at a younger-than-average age may have higher rates of smoking and drinking. Researchers have speculated that this is related to the low self-esteem or rejection such “early maturers” may feel.

However, Patton said, his team’s findings suggest that these children have higher rates of substance use than their peers simply because they’ve moved into puberty, and not because of their reaction to it. Pubertal stage showed a similar influence on older adolescents in the study as it did on younger ones.

Reporting in the journal Pediatrics, Patton and his colleagues note that puberty may have physiological effects that sway the tendency toward substance use. Animal studies, for example, have shown increases in “novelty-seeking,” which is linked to a brain area implicated in substance abuse.

For their study, the researchers surveyed 5,725 students in Washington state and Victoria, Australia, on substance abuse, pubertal development and relationships with family, friends and school.

Overall, 36 percent of Australian students and one-quarter of U.S. students said they had ever smoked or used alcohol or marijuana. Twenty-seven percent and 13 percent of Australians and Americans, respectively, reported regular substance use.

The researchers found that students in late-stage puberty were three times as likely - and those in mid-stage puberty were twice as likely - as those in early puberty to have ever used tobacco, alcohol or marijuana. Their risks of regular substance use were similar.

One explanation, the researchers found, was that students in late puberty had more friends who drank or smoked cigarettes or marijuana. This peer influence had a strong effect on substance use, though it did not fully account for the increased risk linked to late-stage puberty.

According to Patton, puberty seemed to “drive a different pattern of social affiliation,” such that kids who were well into puberty were more likely than others to choose friends who were smoking, drinking or using pot.

The findings, the researchers conclude, underscore the importance of preventing substance use among younger teens. According to Patton, this includes the willingness of parents and communities to take a harder line, and not, for instance, accept drinking as something that teenagers do.

In the study, kids who reported stronger connections to their parents or schools also reported less substance use.

SOURCE: Pediatrics, September 2004.