Study suggests those with “normal blood pressure” still at risk.
The body mass index (BMI) of seemingly healthy teens in 11th or 12th grade should be checked to predict whether they are likely to develop hypertension (high blood pressure) as young adults. This is the lesson of a new study by Ben-Gurion University of the Negev researchers who just published their findings in the journal Hypertension of the American Heart Association.
The BMI can easily be calculated by dividing one’s weight in kilos by the square of one’s height in meters (or in non-metric countries, the number of pounds multiplied by 703 and divided by one’s height in inches squared). Anyone with a BMI over 25 is considered overweight; if it is over 30, the person is obese.
BGU clinical biochemistry Prof. Assaf Rudich, who headed the large-scale prospective study, said that despite “normal” blood pressure at age 17, hypertension can develop a few years later. The team also found that teenage boys are three to four times more likely to develop high blood pressure in early adulthood than girls.
Currently, systolic blood pressures (the top number of the reading) of 100 to 110 and even up to 120 are considered within the normal range for adolescents. But if their BMI is too high, they may be in trouble and having a lower blood pressure at 17 should now be regarded as desirable, Rudich said.
Known as the “silent killer,” hypertension is a major risk factor for heart disease and vascular diseases like stroke, he said. “It is increasing along with the obesity epidemic, but regrettably young adults who are otherwise healthy frequently are not screened for becoming hypertensive.”
The BGU researchers examined the development of blood pressure from adolescence to young adulthood in 23,191 men and 3,789 women from the ages of 17 when undergoing medical tests for the Israel Defense Forces and followed them up until the age of 42. They took regular readings of blood pressure and BMI of teenagers who did not have high blood pressure at 17.
The study showed that in boys, there is a strong correlation between blood pressure and BMI at 17, meaning that while the blood pressure reading may be in the “normal range,” there is a greater risk for hypertension when BMI is also evaluated.
The rate of progression to hypertension is higher in boys whose systolic blood pressure is 110 versus those whose blood pressure is 100.
For girls, only the sub-group considered obese had substantially higher risk of high blood pressure. The researchers believe that the hormone estrogen may protect against hypertension.
The study also confirmed the observation that 17-year-old boys have higher blood pressure than girls of the same age. During a follow-up period with these adolescents, 14 percent or 3,810 people developed hypertension.
“Collectively, the study suggests that pediatricians caring for adolescents and physicians caring for young adults should be more aware of the need to monitor weight and blood pressure even when they are considered normal,” said Prof. Iris Shai of the Faculty of Health Sciences‚ epidemiology department.
“For the individual person, a ‘normal value’ may still be associated with a significant elevated risk of disease when the BMI and sex of the patient is also considered,” she concluded.