Increasing numbers of children have high blood pressure, largely as a consequence of their obesity. A growing body of evidence suggests that high blood pressure may impair children's cognitive skills, reducing their ability to remember, pay attention and organise facts.
In the most comprehensive study to date, published on Thursday in The Journal of Pediatrics, 75 children ages 10 to 18 with untreated high blood pressure performed worse on several tests of cognitive function, compared with 75 peers who had normal blood pressure.
The differences were subtle, and the new research does not prove that high blood pressure diminishes cognitive skills in children. Still, the findings set off alarm bells among some experts. "This study really shows there are some differences," said David B Kershaw, the director of pediatric nephrology at C S Mott Children's Hospital at the University of Michigan, who was not involved with the research. "This was not just random chance."
Marc B Lande, a professor of pediatric nephrology at the University of Rochester Medical Center, and his colleagues had children tested at four sites in three states, matching those with and without high blood pressure by age, maternal education, race, obesity levels and other factors.
The researchers excluded children with learning disabilities and sleep problems, which can affect cognitive skills. Children with elevated blood pressure performed worse than their peers on tests of memory, processing speed and verbal skills, the researchers found. But all the scores were still in the normal range.
Because of increased obesity, elevated blood pressure, also called hypertension, is no longer rare in children, though it is underdiagnosed. In a recent survey, about 3.5 per cent of 14,187 children ages 3 to 18 had hypertension.
"Most people don't understand that cardiovascular risk factors - in this case, hypertension - can affect thinking and memory, and certainly they don't think there could be an effect in childhood," said Kristine Yaffe, a professor of psychiatry, neurology and epidemiology at the University of California, San Francisco, who has researched the effects of cardiovascular risk factors on cognition.
Lande and his colleagues noted that children with high blood pressure tended to have other risk factors that might negatively affect cognition, including insulin resistance and obstructive sleep apnea.
Children who had a formal diagnosis of obstructive sleep apnea were excluded from the new study, but some adolescents with poor sleep participated. Dr. Lande said the study found "that the presence of hypertension made the effect of poor sleep on cognition even worse."
Lower scores on cognitive tests do not necessarily indicate that a child is struggling in everyday life, experts cautioned.
"Yes, there are certain differences, but what they mean in terms of life functioning isn't clear," said Dr. Julie R. Ingelfinger, a professor of pediatrics at Harvard Medical School and a senior consultant in nephrology at Massachusetts General Hospital.
But, she added, "We know from other studies that problems with memory, attention and cognitive function have a lot to do with how well you do in your job and at school."
Children may be uniquely susceptible to cognitive deficits, Dr. Kershaw said. "One of my concerns is, if you have high blood pressure and you're 10 to 18 years old, it may impact your cognitive function more than if you're 40 or 50," he said.
The areas of the brain that control executive function mature until a person's early 20s. So the idea is that perhaps hypertension could hinder that function, Dr. Kershaw said.
Observational studies have shown that having high blood pressure in one's early 40s to 60s increases the risk of cognitive decline later in life. Clinical trials have not shown, however, that controlling high blood pressure with drugs or lifestyle changes can prevent cognitive problems.
More research is needed to decipher whether treating children who have high blood pressure with dietary changes, exercise or medication could improve their cognitive ability. The work is already underway: The 75 children with hypertension in the latest study are being treated and followed for a year. The last child will finish the study early next year, Dr. Lande said.
"Then we'll be able to know if subtle neurocognitive differences between hypertensive kids and the controls go away with treatment or not," he said.
Dr. Ingelfinger applauded the "carefully done" research, but said she was more interested in seeing the follow-up research. "The most important thing is, if blood pressure is controlled, do these cognitive changes go away?"
© 2016 The New York Times News Service
