For harried parents, the idea that raising children can lower your blood pressure seems counterintuitive. So it came as a surprise to a local researcher when she came to that conclusion during a recent study.

"From personal experience, I thought it would go the opposite direction," said Julianne Holt-Lunstad, assistant professor of psychology at Brigham Young University, whose study on the phenomenon was published Thursday in the Annals of Behavioral Medicine.

"While caring for children may include daily hassles, deriving a sense of meaning and purpose from life's stress has been shown to be associated with better health outcomes," Holt-Lunstad said.

The study involved 198 local adults, ages 20 to 68, all of whom were married, and 70 percent of them had children. Subjects wore portable blood pressure monitors that took measurements at random intervals during a 24-hour period, including sleep time.

The result? For parents overall, the 24-hour blood pressure readings averaged 116/71 — which put them 4.5 points lower than nonparents in systolic blood pressure (the first number) and 3 points lower than nonparents in diastolic blood pressure.

The effect was dramatic among women in particular, with motherhood corresponding to a 12-point difference in systolic blood pressure and a 7-point difference in diastolic blood pressure.

"We knew that these findings are going to seem counterintuitive and people would be very surprised, particularly with a study coming out of Utah," she said. "There will certainly be a lot of skepticism out there, so we've been careful to look into what explains it."

Using statistical analysis, the researchers were able to control for factors already known to influence blood pressure: age, body mass, gender, exercise, employment, diet and smoking.

They also controlled for different parenting stages. "I thought maybe there would be different stages that are more stressful for parents — primarily people with babies or teens — but the effect is consistent across various stages of parenting," Holt-Lunstad said.

So why did parents register lower blood pressure numbers than their nonparent peers? "We can't say for sure what it is, but we have been able to … identify a few probable ones," she said.

Biology may play a role, she said, noting the finds are consistent with some animal research that shows a "pregnancy protection" in the hormones generated during lactation that are shown to be associated with better stress regulation in animals. "If they're more protected against stress, they're better at protecting their young."

Psychology also may play a role, because "people with stress that are able to find meaning in it cope with it better. Parenting is a very meaningful activity," and that may help explain the less detrimental effect of stress that comes from parenting, she said.

Research also shows that parents have larger social networks because they're involved with others in their children's activities, and large social networks are correlated with better health.

Diet may also play a role, she said, noting that "if you're encouraging your children to eat healthy, you're probably eating healthy, too."

Parents also may engage in less-risky behaviors based on their responsibility to be healthy and well for their children.

Finally, she said, couples without children "may incur stress associated with violating the social norm" or expectation that they will have children. "Some couples may wish to be parents and aren't, or can't be, and there may be stress with that. Other couples may not wish to be parents but get a lot of negative social pressure to do so."

None of those factors is definitive, she said, noting the need for more research to determine what is driving blood pressure down for parents.

"I would imagine if you looked at parents during particular points in time, you may see their blood pressure elevated, but if this (potential) biological protection is valid, it would suggest when we face those frustrating moments or challenges, as parents we may be less reactive to it or better able to cope with it."