Jan. 20, 2006 -- Big brothers and sisters may play a big role in whether their younger siblings smoke tobacco and drink alcohol.
In fact, older siblings may be more influential than parents or friends, according to a new study.
It boils down to behavior. If a big brother or sister drinks or smokes, their younger sibling is more likely to follow in their footsteps.
Kids also tend to copy their parents' behavior to a slightly lesser degree, the new study shows.
It might be a good idea to get older siblings to help discourage younger kids from smoking and drinking, write Abigail Fagan, PhD, and Jake Najman, PhD, in the Journal of Drug Issues.
Fagan now works at the University of Washington. Najman directs the Queensland Alcohol and Drug Research and Education Centre at Australia's University of Queensland.
Following Older Sibling's Example
The study included 1,370 children and their mothers in Brisbane, Australia. The moms reported their smoking and drinking habits starting during pregnancy. The children consisted of 685 pairs of siblings who were one to three years apart.
When the kids were 14, they answered questions about whether they had used alcohol or tobacco, and if so, how often.
If an older sibling reported smoking, their younger brother or sister was four times as likely to report smoking at age 14.
A similar pattern held for drinking. Younger siblings were three times as likely to report drinking at age 14 if their older brother or sister had done so at the same age.
"Tobacco and alcohol use are more likely among younger siblings who have older siblings engaging in these behaviors, compared to those whose siblings abstain," the researchers write.
What About Parents?
Parents' smoking and drinking was slightly less influential, but still important, the study shows.
"Sibling substance use has a greater effect on adolescent substance use than does smoking or drinking by parents," the researchers write.
They add that children were also more likely to report smoking or drinking if their mothers were depressed.
Some of the teens may have tried smoking or drinking as a one-time experiment. But experimentation at a young age often paves the way for long-lasting habits, write Fagan and Najman.
The researchers took into account any influence parents' behavior may have had on both younger and older siblings. However, they aren't sure if other factors -- like genes and parental supervision -- made a difference.
Older siblings could prove helpful in efforts to discourage teenage smoking and drinking, the researchers suggest. They note that younger kids might copy elder siblings or get cigarettes and alcohol from their big brothers and sisters.