TUESDAY, Dec. 11 (HealthDay News) -- When it comes to lowering children's blood pressure, the amount of exercise they get may be more important than the intensity.

That's the suggestion of a British study of 5,505 boys and girls, ages 11-12, who wore movement detectors for a week.

The researchers found that a higher amount of total physical activity was associated with almost half a millimeter of mercury reduction in both systolic and diastolic blood pressure. The study findings were published Dec. 11 in the journal Hypertension.

"Even after taking into account a number of possible confounding factors, such as social class and maternal health, associations between physical activity and blood pressure were weakened, but remained. If these associations translate into those of similar magnitude in adulthood, this could be of public health significance," lead author Sam Leary, a lecturer in statistics at the University of Bristol's Department of Oral and Dental Science, said in a prepared statement.

The researchers did find that 15 minutes a day of moderate to vigorous activity was associated with lower blood pressure of at least a half a millimeter of mercury. However, when they looked at total amounts of exercise and moderate and physical exercise together, they found the association between amount of activity and blood pressure remained similar, while the association between moderate and vigorous exercise and blood pressure was substantially weaker.

"Our study findings suggest that encouraging children to increase their levels of physical activity may help reduce their current blood pressure. The higher levels of physical activity likely will track into adulthood and be associated with a lower adult blood pressure and thus contribute to a reduction in cardiovascular risk," Leary said.

Only 5 percent of the boys and 0.5 percent of the girls in the study met the recommended guidelines for 60 minutes of moderate to vigorous physical activity a day. The median was 25 minutes a day for boys and 16 minutes a day for girls.

Children that met the guidelines had, on average, 2 mmHg lower systolic and 1 mmHg lower diastolic blood pressure readings than those who didn't meet the guidelines.

SOURCE: American Heart Association, news release, Dec. 11, 2007