Nancy Brown, chief executive officer of the American Heart Association, said it's recommended children eat 1,500 milligrams a day.
The study, published in the journal Pediatrics, found the number of obese youth increased 74 percent for every 1,000 milligrams of increased sodium intake per day -- compared with only a 6 percent increase among normal-weight young people.
"It's very disturbing that this nation's children and teens consume too much salt in their diets at school and home. High blood pressure, once viewed as an adult illness is now affecting more young people because of high sodium diets and increasing obesity," Brown said in a statement. "While new nutrition standards for school meals are helping, progress is slow."
More than 75 percent of sodium in the U.S. diet comes from processed and restaurant foods, as well as beverages, Brown said.
Too much sodium is linked to high blood pressure, a major risk factor for heart disease, stroke and other health problems, Brown added.
"The salt we all eat daily is becoming a major public health issue and current approaches to sodium reduction in the United States have not been effective," Brown said. "We must make the reduction of sodium a national priority."