DALLAS, Sept 10 (Reuters) - Blood pressure levels among American children are on the rise, an alarming trend linked to climbing obesity rates that reverses decades of decline, researchers reported on Monday.

The study, published this week in the American Heart Association journal Circulation, adds to a growing body of evidence linking swelling juvenile waistlines with rising blood pressure and other cardiovascular problems.

The researchers looked at data from seven U.S. government surveys conducted from 1963 to 2002 on youngsters aged 8 to 17.

They looked at trends in blood pressure and "pre-high" blood pressure adjusted for age as well as variations among ethnic and racial groups and the impact of increasing obesity on these trends.

They found that each 0.4 inch (1 cm) increase in waist circumference raised the likelihood of high blood pressure by 10 percent and the likelihood of pre-high blood pressure by 5 percent.

Pre-high blood pressure was defined as either the systolic or diastolic blood pressure falling between the 90th percentile and the 95th percentile. High blood pressure was for readings above that.

"The prevalence of high blood pressure and pre-high blood pressure in children and adolescents showed a downward trend between 1963 and the 1988-94 survey. But the trend began to reverse through 2002," the Heart Association said in a statement.

Just over 11 percent of children and teens had high blood pressure in 1980, the Heart Association said. That fell to 2.7 percent in the 1988-94 survey, but rose to 3.7 percent in the latest survey done in 1999-2002.

The trend was most pronounced among Mexican-American males, who were included in the surveys for the first time from 1982. The survey found that 5.3 percent of these young men had high blood pressure in 1999-2002, the Heart Association said.

"Unless this upward trend in high blood pressure is reversed, we could be facing an explosion of new cardiovascular disease cases in young adults and adults. To reverse the upward trend at the beginning is good, and that's why we need to act now," said Dr. Rebecca Din-Dzietham, associate professor of community health and preventive medicine at Morehouse School of Medicine in Atlanta, Georgia.

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