And those are only the immediate effects. Scientists don't know what caffeine's long-term effects might be in children.
"What does it do to an 8-year-old's cardiovascular system? Or her brain?" asks Judith Owens, director of the Center for Pediatric Sleep Disorders at Boston Children's Hospital. "There's really no reason for kids to have caffeine."
And yet American kids are eating and drinking caffeine-containing products. Results from annual surveys conducted by the Centers for Disease Control and Prevention found that 73 per cent of Americans from age 2 to 22 consume caffeine on any given day. In the first survey year, 1999-2000, 63 per cent of it came from soda, but that declined to 38 percent in the last survey year, 2009-2010.
Over that same time frame, the proportion of caffeine coming from coffee increased from 10 per cent to 24 per cent, and caffeine from energy drinks grew from nothing to 6 per cent. (The overall amount of caffeine held steady from 60 to 80 milligrams per day over the 10-year period.)
How much is too much? Unlike US agencies, Health Canada makes caffeine recommendations: no more than 400 milligrams per day for healthy adults, 300 for pregnant or breast-feeding women.
And for kids? A 45-milligram limit for kids age 4 to 6, 62.5 milligrams for kids 7 to 9 and 85 for kids 10 to 12. For adolescents, the recommended limit is 2.5 milligrams per kilogram of body weight.
Owens scoured the scientific literature for studies of how caffeine affects kids and published a paper last year in the journal Nutrition Reviews.
Caffeine does reduce sleepiness, she says. This might be handy for a high school student tackling a mountain of homework. But later, there's a big downside. "You'll have more trouble falling asleep and more sleep disruptions through the night," she said. For a sleep-deprived nation of teenagers, this is not good news.
A study of 191 Ohio middle schoolers found that caffeine intake varied from zero to 800 milligrams per day, with an average of 53 milligrams per day. Students in the study reported their sleep patterns and consumption of caffeine-containing foods for 14 days in a row. Higher caffeine intake was associated with shorter sleep duration at night, increased wakings at night and increased sleeping during the day.
The energy boost is a key reason many adults drink coffee. If you watch commercials for energy drinks, you might be convinced of their capacity to improve just about every aspect of your life. The marketing of energy drinks causes as much concern among caffeine researchers and pediatricians as the ingredients in these beverages, which also include sugar and herbal extracts.
"Party like a rockstar!" says the Rockstar ads. Likewise, Red Bull and Monster sponsor active sports such as BMX biking and skateboarding - and their appealing athletes.
In 2011, the American Academy of Pediatrics published a policy statement declaring that "energy drinks have no place in the diet of children and adolescents." The statement also accused energy-drink makers of marketing to children, a charge that Red Bull quickly denied.
"Red Bull says they don't market to kids, but their Web site is a 13-year-old boy's dream," Owens says.
Some researchers argue that energy drinks are a gateway to other drugs, legal and illegal. Students might graduate from using a shot-size energy drink to sharing a roommate's Ritalin for a better study boost.
"The earlier kids use caffeine, the more likely they are to smoke and to drink alcohol," Owens says. Cause and effect are not clear: It could be that the kids buying into the caffeine messaging are more likely to try out other mind-altering substances as well.
Caffeine can also affect mood - in both positive and negative ways. In a small 2008 study, 30 children (ages 7 to 17) who had been diagnosed with depression averaged five servings of caffeine a day, whereas an age-matched group of 23 kids with no psychiatric diagnoses averaged one serving per day.
"The causality here is not known," says study co-author Jennifer Silk, a psychologist at the University of Pittsburgh. It wasn't clear whether caffeine was contributing to depression or depression was making kids seek caffeine, she says. "We suspected the kids might be self-medicating. When they're sluggish or down, they need a pick-me-up."
Silk's study also found that the kids with depression reported more anxiety on the days they consumed more caffeine.
"I don't see any reason to give kids caffeine," Silk says. "It's used to counter fatigue, low mood and anxiety. But it could be causing those things too."
I think I'll encourage my 11-year-old to order decaf.
