Until now, such research was limited to adolescents. Prior studies showed a link between soft drinks and older children's aggression, depression and suicidal thoughts.
"It makes sense on a lot of levels, and that's what's interesting about this study," said Ben Belnap, a child psychologist at Primary Children's Medical Center in Salt Lake City and the father of four children, ages 2 to 9. "It sort of seems like a no-brainer. "
Although the new study doesn't pinpoint whether it's the sugar or some other ingredient, Belnap said it seems wise to limit consumption.
"It's hard enough being a 5-year-old and learning to navigate in the world," he said. "I'd say, let's make it as easy as we can for these kids and help them have steady blood sugar."
The new study found that any soda at all resulted in more aggressiveness destroying others' things, getting into fights or physically attacking people but more soda meant more aggression, more attention problems and an increase in withdrawn behavior.
"We found that the child's aggressive behavior score increased with every increase in soft drink servings per day," Suglia said in a news release.
The study analyzed 2,929 mothers' answers to questions about their children's behavior at age 5. They were part of The Fragile Families and Child Wellbeing Study, which enrolled several thousand women in 20 cities at the time their babies were born and surveyed them periodically for several years.
The mothers reported that 43 percent of the children drank a serving of soda every day, and 4 percent consumed four or more. The survey didn't ask the size of the serving.
The latest similar data for Utah, by contrast, showed 8.2 percent of children ages 5 to 8 consumed seven or more soft drinks a week, the equivalent of one a day. However, 69 percent had one to six soda drinks per week according to that research, published by the Utah Department of Health in 2008.
Though the new study shows a correlation, it doesn't prove soda makes 5-year-olds aggressive, withdrawn or gives them attention problems. It also doesn't explore what it is about soda that appears to have such effects, whether it's the high-fructose corn syrup, carbonation, preservatives, caffeine or some combination of those ingredients.
The American Beverage Association noted that limitation in a statement Thursday.
"The authors themselves note that their study 'is not able to identify the nature of the association between soft drinks and problem behaviors,' " the association said in a statement supplied by Christopher Gindlesperger, senior director of public affairs.
"It is a leap to suggest that drinking soda causes these or any other behavioral issue. The science does not support that conclusion," the ABA said, also noting that its member companies do not promote or market soft drinks to 5-year-olds.
Belnap said the study will be valuable for him as he tries to get to the bottom of a child's problems.
It may be that a child drinking a lot of soda and exhibiting bad behavior lives in a permissive home with little supervision. He now has research to back up the suggestion that parents set more limits even if only about soda consumption.
Patrice Isabella, a registered dietitian at the Utah Department of Health, notes that soft drinks are just one of the culprits in youngsters' overconsumption of empty calories.
Fruit punch, sports drinks, flavored yogurt, pudding and soda all add up, for most children, to far more than the 120 calories per day a 5-year-old should get from solid fats and added sugars, she said.
She doubts that soda consumption has dropped much among Utah children since the 2008 study was published. "People will buy what's available," she said. "It's a challenge to parents to make their way through the myriad beverages available in the marketplace."