By Alison Trinidad

Teenagers who see friends smoking and drinking alcohol in photographs posted on Facebook and MySpace are more likely to smoke and drink themselves, according to a new study.

“Our study shows that adolescents can be influenced by their friends’ online pictures to smoke or drink alcohol,” said Thomas W. Valente, PhD, professor of preventive medicine at the Keck School of Medicine of USC and the study’s principal investigator. “To our knowledge, this is the first study to apply social network analysis methods to examine how teenagers’ activities on online social networking sites influence their smoking and alcohol use.”

The study appears in the Sept. 3 online edition of the Journal of Adolescent Health.

Valente and his team surveyed 1,563 10th-grade students from the El Monte Union High School District in L.A. County in October 2010 and April 2011 about their online and offline friendship networks and the frequency of their social media use, smoking and alcohol consumption. At the time of the study, El Monte was the ninth largest city in the county, with a population of about 113,500.

The researchers found that the size of one’s online network was not significantly associated with risky behavior. Exposure to friends’ online pictures of partying or drinking, however, was significantly associated with both smoking and alcohol use. Teens whose close friends did not drink alcohol were more likely to be affected by increasing exposure to risky online pictures.

“The evidence suggests that friends’ online behaviors are a viable source of peer influence,” said Grace C. Huang, PhD, MPH, a graduate of the Keck School’s Health Behavior Research program and the study’s first and corresponding author. “This is important, given that 95 percent of 12 to 17 year olds in the United States access the Internet every day, and 80 percent of those youth use online social networking sites to communicate.”

Students who responded to the survey were evenly distributed across gender and on average 15 years old. About two-thirds were Hispanic/Latino and about one-fourth were Asian, which closely reflects the ethnic distribution of El Monte. In April 2011, nearly 30 percent of respondents had smoked and more than half had at consumed least one alcoholic drink. Roughly one-third of students reported having at least one friend who smoked and/or consumed alcohol.

Almost half of all students reported visiting Facebook and Myspace regularly. On average, 34 percent of students had at least one friend who talked about partying online and 20 percent reported that their friends posted party/drinking pictures online.

Further research might examine how online and offline friendships differ in terms of activities and interactions they have with each other, Huang said.

“Little is known about how social media use affects adolescent health behaviors,” said Huang, now a postdoctoral fellow at the National Cancer Institute. “Our study suggests that it may be beneficial to teach teens about how posting risky behaviors online can hurt their friends.”

The study was supported by the National Institute on Alcohol Abuse and Alcoholism (1RC1AA019239-01) and National Cancer Institute (T32 CA-009492028). Co-authors include Jennifer B. Unger, PhD; Daniel Soto, MPH; Kayo Fujimoto, PhD; Mary Ann Pentz, PhD; and Maryalice Jordan-Marsh, PhD.