Persistently high blood pressure, or hypertension, may spell worse heart trouble for black children under the age of 13 than for other children of the same ages, according to research led by scientists at Johns Hopkins Children''s Center and published in the November issue of Pediatrics.
The study analyzed data from 184 children and young adults, 45 of them black, ages 3 to 20, treated at three hospitals for primary hypertension.
Black children were, overall, more prone to left-ventricular hypertrophy (LVH), a dangerous thickening of the heart muscle, one of hypertension''s earliest, most insidious and most common complications, and the difference was particularly pronounced in those younger than 13 years of age, the researchers report.
"The bottom line is to monitor carefully and treat early all children with hypertension because they are all at risk, but pediatricians should also keep in mind that African-American patients may develop worse complications or develop them sooner," says lead investigator Tammy Brady, M.D. M.H.S., a kidney specialist at Hopkins Children''s.
Using a special monitor that automatically takes a child''s blood pressure every 20-30 minutes over 24 hours, the researchers found that black teenagers had more severe hypertension than teens from other races. Not only did black teens have higher blood pressure overall, but their blood pressures remained in the dangerously hypertensive range for longer periods compared to other children. Thus, in black teens, 57 percent of the readings for systolic blood pressure (top number) recorded over 24 hours were dangerously elevated compared to 41 percent for other teens. Nearly 30 percent of the diastolic pressure (bottom number) measurements during 24 hours were abnormally high in black teens, compared to 19 percent in teens form other races.
While the difference in hypertension severity was absent in those under 13, younger black children had higher rates of obesity and overweight (96 percent) than other races (74 percent) and were more likely to have abnormally higher levels of renin, the blood-pressure-regulating hormone produced by the kidneys (8.7 nanograms per milliliter of blood per hour) than other children (3.6). They were more than twice as likely to have thickening of the heart muscle (56 percent) than children of other races (26 percent).
The racial differences in renin levels and LVH disappeared in those 13 years of age or older, a finding potentially due to the higher overweight and obesity among the younger children, the researchers say.
While establishing clear racial differences among children with hypertension, the study findings underscore the need for early diagnosis and prompt treatment of high blood pressure in all children, regardless of race and age. Indeed, more than half of the children in the study were either overweight or obese and more than one-third had heart-muscle abnormalities.
The study did not explore the reasons behind these racial differences, but the researchers hypothesize that they may be related to biological variations, diet, access to healthcare and low birth weight, which is more common in African-Americans and is a well-known risk factor for hypertension.
A single episode of high blood pressure is not necessarily hypertension, but investigators say that all children with one episode of high blood pressure during a visit to the doctor should be monitored. Clinically important hypertension is defined as elevated blood pressure on three consecutive visits. Normal blood pressure values for adults are 120/80 and under, but normal values in children vary by age, gender and height.
All children diagnosed with hypertension should be referred to a kidney specialist and have an ultrasound to check the heart muscle thickness and function.
More than 4 million children in the United States are estimated to have hypertension, a number that has increased five-fold over the last 30 years, likely because of growing obesity in children, among other factors, the researchers say.
The research was funded by the American Society of Nephrology, the National Kidney Foundation and the Thomas Wilson Sanitarium for the Children of Baltimore City.
Co-investigators from Hopkins include Barbara Fivush, M.D., and Rulan Parekh, M.D., M.S. Researchers from other institutions: Joseph Flynn, M.D., M.S., of Seattle Children''s Hospital.