Too much soda can contribute to childhood obesity, but its negative impact may go even farther.

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Black teens who drink several caffeinated drinks each day may increase their blood pressure, according to a study published in the May issue of Archives of Pediatric & Adolescent Medicine.

"This paper indicates that the concern about soda consumption in children and teens should not be limited to the fact that soft drinks add more calories to the diet," said Dr. Margaret Savoca, a nutritionist at the Medical College of Georgia. "Caffeine consumption may also impact their blood pressure."

Savoca and her team studied the blood pressures and caffeinated-beverage intake of 159 healthy black and white adolescents age 15 to 19. They found that the kids who drank the most caffeine -- more than 100 milligrams a day or the equivalent of about four 12-ounce sodas -- had the highest pressures. The top, or systolic, number -- which indicates the pressure inside blood vessels that the heart must beat against -- was the most impacted.

They also found that despite the fact that the teens who drank the most caffeine were white, the blacks' pressures were most impacted. Black adolescents who drank the most caffeine had systolic pressures that averaged 13.9 millimeters higher than blacks who consumed less than 50 milligrams of caffeine; in adolescent whites, the average was only about .2 millimeters higher.

An estimated 68 percent of boys and 62 percent of girls ages 12 to 17 drink one or more soft drinks each day, and about 20 percent of boys and girls drink tea or coffee every day.

The researchers said more studies need to be conducted that look into caffeine's effects on adolescents, both black and white.