MONDAY, Oct. 24, 2011 (HealthDay News) -- Teens who drink lots of soda seem to be prone to violence, new research suggests.
But the study authors concede that sodas are probably not the direct cause of the aggression.
While there's a chance that the sugar and caffeine from carbonated drinks contributes to violent behavior, the study shows an association, not a cause-and-effect. Soda consumption, for example, may be a marker of heightened violent tendencies already present in the teen, or of poor parenting, the researchers said.
"Soda [could be] a red flag that is indicating something else is wrong," said study co-author Sara Solnick, an associate professor of economics at the University of Vermont in Burlington.
The study is published in the Oct. 24 online issue of Injury Prevention.
The researchers asked about 1,900 Boston public high school students how many non-diet sodas they drank during the last week, as well as whether they carried a weapon or had been violent toward family members or peers.
Nearly 43 percent of teens who drank 14 or more cans of soda a week said they carried a weapon at some point, compared with 23 percent of teens who drank less than one can of soda a week.
Th researchers also saw an association between soda and weapons even when kids drank less than 14 cans. About 33 percent of teens who drank two to four cans a week said they'd carried a knife or a gun at some point, as did 38 percent of teens who drank five to seven cans of soda.
There was a similar "dose relationship" on other measures of violence. About 27 percent of teens who drank 14 or more cans of soda a week admitted to violence against a romantic partner, compared with 15 percent of those drinking less than one can a week.
And 59 percent of those drinking 14 or more cans a week had been violent toward peers, compared with 35 percent of those drinking one can or less. Teens who drank lots of soda were also more likely to be aggressive toward a sibling -- 45 percent compared with 25 percent among teens who drank little soda.
The authors were able to control for a number of factors including gender, race and tobacco and alcohol use but not for some other important factors that could affect the likelihood of violence, such as quality of parenting and poverty. Those who reported drinking lots of soda were also more likely to have also used alcohol or smoked cigarettes.
Nearly 30 percent of the ninth to 12th graders said they drank more than five cans of soda a week.
It's possible that the association is explained by the soda itself, researchers said. Teens who drink lots of soda could be missing important micro-nutrients found in healthier foods, according to background information in the study, or could be drinking soda to combat low blood sugar, which is linked to irritability or violence.
Soft drinks also contain sugar and caffeine, which might affect behavior.
But the studies on the effect of caffeine and sugar on behavior are inconclusive, said another expert.
"There's no definitive explanation that this explains how or if this might affect behavior," said Dr. Alan Manevitz, a psychiatrist with Lenox Hill Hospital in New York City.
Alternatively, "soda could be showing that this person is not having a healthy diet or they don't have a great upbringing," Solnick said. "Those things are connected to violence."
In the study, the authors make mention of the infamous "Twinkie Defense" in which defendant Dan White was convicted only of voluntary manslaughter instead of homicide in the deaths of San Francisco city district supervisor Harvey Milk and Mayor George Moscone in 1979.
White's lawyers argued that the crime wasn't premeditated because White was hyped up on junk food and Coca-Cola.
Since then, other studies have further probed possible effects of unhealthy food, with one study finding poor mental health among Norwegian teens who drank a lot of soft drinks. Another study found antisocial tendencies among U.S. college students who consumed a lot of soda.
The U.S. National Library of Medicine has more on teen violence.