NEW YORK -- A happy marriage is good for your blood pressure, but a stressed one can be worse than being single, a preliminary study suggests.

That second finding is a surprise because prior studies have shown that married people tend to be healthier than singles, said researcher Julianne Holt-Lunstad.

It would take further study to sort out what the results mean for long-term health, said Holt-Lunstad, an assistant psychology professor at Brigham Young University. Her study was reported online Thursday by the Annals of Behavioral Medicine.

The study involved 204 married people and 99 single adults. Most were white, and it's not clear whether the same results would apply to other ethnic groups, Holt-Lunstad said.

Study volunteers wore devices that recorded their blood pressure at random times over 24 hours. Married participants also filled out questionnaires about their marriage.

Analysis found that the more marital satisfaction and adjustment spouses reported, the lower their average blood pressure was over the 24 hours and during the daytime.

But spouses who scored low in marital satisfaction had higher average blood pressure than single people did. During the daytime, their average was about five points higher, entering a range that's considered a warning sign. (That result is for the top number in a blood pressure reading).

"I think this (study) is worth some attention," said Karen Matthews, a professor of psychiatry, psychology and epidemiology at the University of Pittsburgh. She studies heart disease and high blood pressure but didn't participate in the new work.

Few studies of the risk for high blood pressure have looked at marital quality rather than just marital status, she said.

It makes sense that marital quality is more important than just being married when it comes to affecting blood pressure, said Dr. Brian Baker, an associate professor of psychiatry at the University of Toronto.