High blood pressure is a major risk factor for heart disease , and the leading cause of stroke .

In adults, blood pressure should be below 120/80. In children and adolescents, however, normal blood pressure varies by age and sex and is determined using a blood pressure table, similar to the height and weight growth charts.

Previous research shows that children who have elevated blood pressure levels often develop high blood pressure as young adults. Once you develop high blood pressure, it usually lasts a lifetime. A risk factor for developing high blood pressure is being overweight. Between 1988 and 2000, the percent of American children who were overweight rose considerably, from 11.7% to 16.3%.

A new study in the May 5, 2004 issue of the Journal of the American Medical Association set out to determine whether along with weight, there was also a change in blood pressure levels among youth between 1988 and 2000. The study found that, in fact, average blood pressure levels among American children and adolescents did increase over the past decade, a finding that they attribute partially to the increase in prevalence of overweight and obesity.

About the Study

This study included 5582 children between the ages of 8-17 who were all part of the National Health and Nutrition Examination Surveys (NHANES) in 1988-1994 or 1999-2000. The average age of the children in both surveys was just under 13 years. In addition, about 50% of the children in each group were males, 16-17% were non-Hispanic black, and 9-12% were Mexican American.

During both of these survey periods, physicians measured blood pressure up to three times using a standard protocol. For this study, the researchers included only those children with at least three valid blood pressure measurements, as well as height and weight measurements.

The researchers compared the systolic and diastolic blood pressure levels for children in the two surveys. (Blood pressure is usually written as a ratio, with the upper number representing systolic blood pressure, and the bottom diastolic blood pressure.) They also looked at the differences when other factors—such as weight, sex, and ethnicity—were taken into account.

The Findings

Overall, systolic blood pressure increased by 1.4 points, and diastolic blood pressure increased by 3.3 points between the two study periods, after adjusting for age, ethnicity, and sex. In 1999-2000 the average blood pressure was 106/61.7 and in 1988-1994 it was 104.6/58.4. After adjusting for body mass index (BMI, a measure of weight that takes into account a persons height) the increase in blood pressure levels was reduced, but they were still higher among the children in the 1999-2000 study period.

Additionally, systolic blood pressure was higher among non-Hispanic blacks and Mexican Americans, than non-Hispanic whites. However, these differences were smaller when BMI was accounted for.

How Does This Affect You?

This study suggests that average blood pressure levels are on the rise among our nations youth, corresponding with the increasing prevalence of overweight and obesity among this population.

However, blood pressure levels were still higher among children in the 1999-2000 study period even after accounting for the subjects’ BMI. This suggests weight is not the only factor influencing blood pressure in children and adolescents. More research is needed to isolate other factors—such as diet and physical activity—that may also be affecting blood pressure independent of weight.

One such study actually appears in this week’s Archives of Pediatric and Adolescent Medicine . The study looked at the relationship between caffeine and blood pressure in adolescents and found that caffeine intake was associated with higher blood pressure levels, particularly among African American youth. But more studies are needed to confirm these results—and to determine whether it was the caffeine or other lifestyle factors associated with caffeine intake that led to the increase in blood pressure.

These studies have significant implications for the future health of our society. Previous research shows that for every one to two point increase in systolic blood pressure, children face a ten percent increased risk of developing high blood pressure as a young adult. And with no signs of the obesity epidemic slowing down, it’s likely that blood pressure levels will continue to rise, pitting our nations youth against a lifetime of health challenges.

Fortunately, most cases of high blood pressure can be avoided through preventive action. The following are some lifestyle guidelines to help decrease the likelihood that your child will develop high blood pressure:

  • Help them to maintain a healthy weight for their height.
  • Encourage them to exercise regularly.
  • Ensure a diet rich in fruits, vegetables, and skim dairy products.
  • Steer them clear of foods high in sodium.

All these steps work just as well in adults too.