Amount of kids' exercise important in lowering blood pressure

The total amount of exercise may be more important than the intensity in lowering blood pressure in children, United Kingdom researchers reported in Hypertension: Journal of the American Heart Association.

In a study of 5,505 boys and girls 11- to 12-years-old who wore movement detectors for a week, researchers found that higher amounts of total physical activity — 100 counts per minute — was associated with lower blood pressure of almost half a millimeter of mercury for both systolic and diastolic blood pressure.

"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," said Sam Leary, PhD, lead author of the report and a lecturer in statistics in the Department of Oral and Dental Science at the University of Bristol, United Kingdom. "If these associations translate into those of similar magnitude in adulthood, this could be of public health significance."

The researchers also found that 15 minutes per day of moderate to vigorous activity was associated with lower blood pressure of at least a half a millimeter of mercury. However, when the researchers studied total physical activity and time spent in moderate to vigorous activity together, the association between blood pressure and physical activity remained similar, while the association between moderate to vigorous exercise activity was substantially weakened.

The study — part of the Avon Longitudinal Study of Parents and Children, based in Bristol, United Kingdom — measured the blood pressure of the children in a research clinic. Researchers then outfitted the children with an accelerometer/movement detector to wear around their waist for seven days. The accelerometer detects movement in the vertical plane recorded as counts. Total physical activity included all activities at all intensities measured as average counts per minute; moderate to vigorous activity was calculated by the average number of minutes per day above 3,600 counts per minute.

Although the relationship between physical activity and blood pressure in adults is well established, findings in children have been inconsistent. Most studies have based physical activity data on self-reported questionnaires that provides a poor measure of activity in children.

Mechanical techniques such as accelerometers may provide a more accurate measure of activity in children, Leary said. "Therefore, our study provides invaluable data. In addition to its large size, it is one of the few to use accelerometers and the first to our knowledge to compare the volume and intensity of activity with respect to associations with blood pressure in childhood."

Few of the children in the study had high blood pressure. The average systolic blood pressures were 104.8 mmHg for boys and 106.0 mmHg for girls. The average diastolic blood pressures were 58.3 mmHg for boys and 59.1 mmHg for girls.

The median physical activity was 645 counts per minute per day for boys and 529 counts per minute for girls. The median amount of time spent in moderate to vigorous activity was 25 minutes daily for boys and only 16 minutes daily for girls — well short of the recommended 60 minutes a day. Only 3 percent of the children (5 percent of boys and a half percent of girls) met the guidelines, researchers reported.

Researchers found that children meeting the activity guidelines had blood pressure levels that were on average 2 mmHg and 1 mmHg lower for systolic and diastolic, respectively, than those who did not meet the guidelines.

"Any activity other than lying or sitting contributes to the total volume of activity so if, for example, children chose to walk to and from school instead of riding in a car, their overall level of physical activity would increase," Leary said. "Moderate to vigorous activity includes anything where you work up a sweat, such as fast walking, running or jogging."

A previous study (Lancet - 1990;335:765-774) in adults showed that a reduction of 5 mmHg in diastolic blood pressure was associated with a decrease of at least 34 percent for stroke and 21 percent in coronary heart disease.

"So the lower levels of blood pressure observed in the current study with physical activity could lead to reductions in these diseases," Leary said. "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 called for further studies in children using mechanical measurements of physical activity to confirm the results observed in the current study, "in particular the idea that it is the total volume rather than the intensity of activity that should be increased should be further investigated."

The National Heart, Lung, and Blood Institute and the Wellcome Trust funded the study.

Co authors are: Andy Ness, M.R.C.P., Ph.D., F.F.P.H.; Calum Mattocks, M.Sc.; Kevin Deere, B.Sc.; Steven Blair, P.E.D.; and Chris Riddoch, Ph.D.

Editor's note: To combat the growing epidemic of childhood obesity, the American Heart Association and the William J. Clinton Foundation, joined forces in 2005 to create the Alliance for a Healthier Generation. The Alliance is working to stop the nationwide increase in childhood obesity by 2010 and is taking bold, innovative steps to help all children live longer and healthier lives. The Alliance is positively affecting the places that can make a difference to a child's health: homes, schools, restaurants, doctors' offices, and the community. For more information please visit www.healthiergeneration.org.