Children and teenagers with high blood pressure may have more difficulty with memory, planning and tackling complex tasks than their peers do, a small study suggests.

The study included 64 subjects who were 10-to-18 years old; half had hypertension while the other half had normal blood pressure levels. The researchers found that those with high blood pressure showed subtle differences in thinking, memory and attention, based on their parents' responses to a standard questionnaire, compared with their counterparts with normal blood pressure.

What's more, the 17 children who were both obese and had high blood pressure were more likely than the others to have symptoms of anxiety and depression. More than half had symptoms serious enough to warrant treatment, the researchers report in the Journal of Pediatrics.

The reasons for the findings are not clear, according to lead investigator Dr. Marc B. Lande of the University of Rochester Medical Center, New York and associates.

"This study can't tell us that this is cause-and-effect," Lande told Reuters Health.

He also stressed that children with high blood pressure had cognitive scores within normal range. The survey used in the study — an 86-item questionnaire completed by parents — is designed to pick up subtle differences in children's thinking, emotional control and behavior.

Still, Lande said, the concern is that high blood pressure might cause subtle damage to children's brain over time. "We don't know that yet,"

he said. "That's where we need further studies."

It will also be important, Lande noted, to see whether treating children's high blood pressure prevents any effects on cognition.

As to why the combination of obesity and hypertension was linked to anxiety and depression, the reasons are, again, unknown. Children in the study who were overweight but had normal blood pressure were not at elevated risk, Lande pointed out.

Whatever the reasons, the finding is one that parents and doctors should be aware of, according to Lande — especially because the recent rise in hypertension among children is largely driven by growing rates of obesity.

"I think that parents and practitioners should be aware that children who have obesity-related hypertension are at risk of anxiety and depression," Lande said.

The American Heart Association recommends that all children ages 3 and older have their blood pressure checked yearly. Diet changes and exercise are usually the first-line treatment, though some children also need medication.