Most young children drink caffeine. They drink lots of it, and many start as young as 5 years old.

THE GIST

A new study finds that three-quarters of young children consume caffeine, typically in the form of soda.

Scientists don't yet know what the health effects of caffeine are on kids, or how much is too much.

Caffeine doesn't seem to make bed-wetting worse, but it probably interferes with sleep.

Three-quarters of young kids consume caffeine, found a new study. Some drink up to three cans of soda a day, and many start as early as age 5.

The study was originally designed to look at the link between caffeine consumption and bed-wetting -- and, to the researchers' surprise, results showed no such connection. But sleep declined as caffeine use went up.

Just by looking at caffeine use in kids in the first place, the study helps by drawing new attention to the widespread use of a stimulant that has unknown health consequences on young bodies.

"Caffeine is not some boogie man, but at some point for all of us, too much caffeine is a problem," said William Warzak, a psychologist in the department of pediatrics at the University of Nebraska Medical Center in Omaha.

"We just don't know where to draw the line for kids," he added. "The take-home point is that parents need to be aware of what their children are eating and drinking."

Warzak is an expert in bed-wetting disorders. Based on anecdotal evidence, he said, doctors often tell parents to give their bed-wetting kids fewer liquids at night and to cut out caffeine, which is a known diuretic.

To test that advice, Warzak and colleagues surveyed the parents of more than 200 kids, ages 5 to 12, during routine visits to an urban pediatric clinic in the Midwest. Parents answered questions about what their kids ate and drank, how much they slept and whether bed-wetting was a problem.

Caffeine use did not seem to affect bed-wetting, the researchers report in the Journal of Pediatrics. But the habit of consuming caffeine was widespread.

Seventy-five percent of kids in the study consumed caffeine, mostly in the form of soda. And they drank a significant amount of it.

According to parents' reports, kids between ages 5 and 7 consumed an average of 52 milligrams of caffeine per day, while eight-through 12-year-olds took in an average of 109 milligrams. A typical 12-ounce can of soda contains between 35 and 55 milligrams.

The United States Food and Drug Administration doesn't offer caffeine guidelines for kids. But the Canadian government recommends an upper limit of 62 mg per day for 7- to 9-year-olds, and 82 milligrams for children up to age 12.

Some kids in Warzak's study were exceeding those recommendations by 25 percent or more. True consumption levels may be even higher than what the study picked up, he added, especially for older kids who often do things their parents don't know about.

For adults, caffeine seems to be mostly benign up to the FDA-recommended limits of 300 milligrams a day, which is equivalent to about three cups of brewed coffee.

But when it comes to young people, there is almost no evidence to say how much is too much or what the health effects might be, said Jennifer Temple, a behavioral neuroscientist at the University of Buffalo in New York. Still, there are some concerns.

Sleep is a big one. Lost sleep in kids has been linked to emotional, learning, safety and health problems. And the new study found that 25 percent of kids in the younger group and most of the older ones slept less than recommended amounts.

Caffeine might also make kids more sensitive to much harder drugs, Temple added. In rat studies, at least, animals that consume caffeine get more pleasure out of cocaine and are more likely to use those drugs again.

In her work, Temple has also found that kids who consume caffeine with sugar end up liking sugary foods better and eat more of those foods compared to kids who don't get any caffeine. Other data suggest that pairing caffeine with certain flavors conditions a taste preference for those flavors.

What all of that means, Temple said, is that drinking sugar-filled caffeinated beverages -- a common combination in sodas and loaded energy drinks -- could lead kids down an insidious path toward both tooth decay and obesity.

"We know that a can of soda here and there is not going to be detrimental, and I don't think anyone would support going out with this alarmist-type message," she said. "But we really have no idea what 200 to 400 milligrams every day in a 13-year-old kid is going to do. We don't have data on that. That's the problem, really."