Do you know your child’s blood pressure?

Amid the world-wide obesity epidemic and broader concerns about improving heart health, blood pressure has emerged as an important question—for kids of any weight. Rising rates of hypertension among overweight kids is driving the concern, but genetics and rare medical problems also may be triggers. While high-blood pressure is generally considered an adult medical problem, its increasing prevalence among children and teenagers is putting many young people on an early trajectory for heart attacks, strokes and other serious problems.

“The foundation of cardiovascular disease develops during childhood,” says Nathalie Farpour-Lambert, who heads the pediatric exercise medicine and obesity care program at University Hospitals of Geneva, in Switzerland. “There is evidence that from the age of 4 we can see the first signs of atherosclerosis,” Dr. Farpour-Lambert says. “Forty years later, it results in coronary heart disease.”

An estimated 5% of people age 18 and under have hypertension, up from about 1% three decades ago—largely reflecting the increased number of obese and overweight kids. The hypertension rate could actually be higher.

In West Virginia, a project over the past 12 years screened 60,000 fifth-graders for heart-risk factors and found 14% of youngsters considered at normal weight, and 21% considered overweight but not obese, had high blood pressure.

Just as with adults, a large portion of kids in potential trouble don’t even know it. “It’s an important health issue in youth and it’s getting worse instead of better,” says Reginald Washington, a pediatric cardiologist and chief medical officer at Rocky Mountain Hospital for Children, in Denver.

Researchers at Cincinnati Children’s Hospital, in Ohio and elsewhere have linked pediatric high blood pressure with enlarged hearts and early stages of disease in the arteries, especially in kids who are overweight or obese. Enlargement of the heart, known by doctors as left ventricular hypertrophy, or LVH, is a thickening of the heart’s main pumping chamber that results from the extra work the heart must do to pump against the resistance caused by high blood pressure.

“The heart is a muscle,” says Tammy M. Brady, a pediatric nephrologist at Johns Hopkins Children’s Center, in Baltimore. “If I’m lifting weights, my arm muscle is going to get bigger. When my heart is pumping against higher blood pressure, it’s going to work harder and get bigger.”

Children love it when their biceps get bigger. But it’s not good to have a thick heart muscle unless it is acquired through athletic conditioning. The periodic exertion followed by rest and recovery that is part of working out can thicken an athlete’s heart and make it more efficient, doctors say. In contrast, enlargement resulting from chronic, unremitting hypertension weakens the heart, causing it to stiffen. That compromises pumping function and ultimately will put an adult at risk of heart attack, heart failure and heartbeat irregularities that may cause sudden cardiac arrest.

“Kids generally don’t have heart attacks or heart failure,” Dr. Brady notes. “But if an 8-year-old has LVH, what are they going to look like as an adult?”

William A. Neal, pediatric cardiologist at West Virginia University and director of a screening project in West Virginia public schools, says, “When you tell a parent their child’s heart has thickened somewhat because of hypertension, that gets their attention.”

The good news is that most young people can achieve healthy blood pressure and reverse the accumulated bad effects by increasing physical activity, improving their diet and losing weight. Medicines generally aren’t required.

The first step is to know your child’s blood pressure. Long-established guidelines call for children starting at age 3 to have their blood pressure checked at every doctor visit. Surveys indicate that in as many as half the cases, that doesn’t happen.

Even when doctors or nurses do take children’s blood pressure, potentially troublesome readings are sometimes missed or ignored. A recent study in the journal Pediatrics by Dr. Brady and her colleagues found that 87% of tests indicating elevated blood pressure among 726 children at an inner-city clinic went unrecognized by the providers giving the tests.

Clinicians sometimes don’t have time to do an accurate blood-pressure test in kids. It takes three consecutive readings to confirm the diagnosis.

With adults, a straightforward reading of, say, 135/90 is all a doctor needs to guide treatment. But in children, what qualifies as hypertension varies widely by height, age and gender. A child’s blood-pressure reading has to be matched up on a chart correlating blood-pressure rankings with heights for boys and girls.

For example, for a 5-year-old girl in the 25th percentile for height, normal blood pressure is 91/53, borderline is 105/67 and high blood pressure is 108/71 or above, according to national blood-pressure guidelines. For an 8-year-old boy in the 75th percentile for height, normal blood pressure is 100/60, borderline is 114/74 and high blood pressure is 118 /79 or above. For a 12-year-old girl in the 90th percentile for height, normal is 108/64 , borderline is 121/78 and high is 125/82 or above.

For adults, optimal target blood pressure is 120/80 or lower; 140/90 or above is considered high.

Diagnosis isn’t a life sentence. A study by Geneva’s Dr. Farpour-Lambert, published in December in the Journal of the American College of Cardiology, showed that after just three months, a regular program of physical activity for obese children led to significant reductions in blood pressure and improvements in the health of their arteries.

Dr. Farpour-Lambert and colleagues assigned 22 children, on average 9 years old, to a program of 60 minutes of physical activity three times a week, and another 22 children to their usual activity. After three months, children in the exercise group had significant lowering of blood pressure that wasn’t linked to weight loss. At six months, other measurements revealed their arteries were healthier and more elastic, and thickening of the neck arteries, an early sign of cardiovascular disease, had stabilized. The study didn’t call for specific diet restrictions, but researchers found those in the exercise group consumed slightly fewer calories than the control group. Time away from the house and the television was time away from unhealthy eating, Dr. Farpour-Lambert suggests. “Instead of putting kids on diets, it’s better to encourage them to play sports,” she says. “They get busy, they get great effects on their health and during that time, they’re not in the fridge.” Among other things, she says the findings support more time for physical activities at schools.

Experts say some attention to diet, though, is a good thing—especially reducing salt, which contributes to high blood pressure and is ubiquitous in fast-food meals. Aerobic exercise as well as some use of weights for resistance-training is beneficial, although Rocky Mountain Hospital’s Dr. Washington cautions that kids with high blood pressure shouldn’t engage in heavy weightlifting, which can make blood pressure worse.

For kids whose blood pressure may result from genes or causes other than being overweight, similarly healthy regimens are the right prescription, he adds. Kids who say, “It’s my mother’s fault so I can eat whatever I want,” increase their risk of future heart problems, Dr. Washington says. “If they do all the wrong things, it’s going to be worse than if they do all the right things.”

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