Michelle Healy

USA TODAY

Despite changes in the types of caffeine consumed%2C young people%27s caffeine intake has not increased

73%25 of children%2C teens and young adults%2C ages 2-22 consumed caffeine on a given day

Insufficient evidence is available to determine how much caffeine is safe for kids and teens

The sources of caffeine consumed by kids, teens and young adults have become more varied over the past decade, but overall intake has not increased, an analysis by federal researchers shows.

Between 1999 and 2010, 73% of people ages 2 to 22 consumed at least some caffeine on a given day, including 63% of children ages 2 to 5, according to the analysis in the March issue of Pediatrics, published online today.

The American Academy of Pediatrics discourages caffeine consumption by young people and said in a 2011 statement that "stimulant-containing energy drinks have no place in the diets of children and adolescents."

Using nationally representative health and nutrition survey data, researchers report:

• The portion of caffeine Intake from soda declined from 62% in 1999-2000 to 38% in 2009-2010.

• Coffee accounted for only 10% of caffeine intake in 1999 -2000, but grew to nearly 24% of intake in 2009-2010.

• Energy drinks, which did not exist as a category tracked by the U.S. Department of Agriculture in 1999-2000, represented nearly 6% of caffeine intake in 2009-2010.

"If soda intake had not decreased over that time, then we certainly would have seen an increase in caffeine intake," says Amy Branum, a health statistician with the National Center for Health Statistics and co-author of the report, the first to examine caffeine trends among teens and kids since energy drinks became widely available.

Energy drinks' contribution to caffeine intake among young people represented "quite a difference in a relatively short amount of time," Branum adds.

Although caffeine is considered a "safe" substance by the Food and Drug Administration, "because of the relative lack of empirical data on children and adolescents, we just don't know whether or not that's true at that age or what the impact is over the long term of higher caffeine consumption," says Jennifer Temple, director of the Nutrition and Health Research Laboratory at the University of Buffalo. Temple, who is researching the effects of caffeine intake in kids and adolescents, was not involved in the new study.

Excess caffeine consumption can increase heart rate and blood pressure, hyperactivity and anxiety, the new study notes. And "case reports of caffeine toxicity and deaths among adolescents and adults reflect the potential dangers of excess caffeine or energy drink consumption," it says.

But caffeine also has some effects that are "thought to be more positive," such as increasing alertness and energy and reducing fatigue, says Temple.

For healthy adults, FDA has cited 400 milligrams a day (the amount contained in about three 8 oz. cups of brewed coffee) "as an amount not generally associated with dangerous, negative effects." The agency has not set a safe level for children.

In May, citing concerns about the growing number of food products with added caffeine, including waffles, jelly beans, gum and nuts, FDA said it would begin to investigate caffeine's potential side effects on kids and adolescents.

Among other study findings:

• Among kids ages 2 to 5, tea overtook soda as the largest contributor to caffeine intake In 2009-2010. Tea, in fact, was the second largest contributor to overall caffeine intake for all ages and remained relatively stable over the decade.

• Among 19- to 22-year-olds, coffee edged out soda as the primary source of caffeine, growing from 14% of intake to 34%. Energy drinks went from 0% in 1999-2000 to 10%.

• Among all age groups, ages 12 to 16 had a the greatest intake of caffeine from sodas in 2009-2010 (46%) down from 65% in 1999-2000.