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Every marriage has highs and lows from time to time, but some relationships are both good and bad on a regular basis. Call it the ambivalent marriage — not always terrible, but not always great, either.

While many couples can no doubt relate to this not bad, but not good, state of affairs, new research shows that ambivalence in a relationship — the feeling that a partner may be unpredictable with his or her support or negativity — can take a quiet toll on the health of an individual.

The findings, published this month by researchers at Brigham Young University, are part of a growing body of research that attempts to parse the so-called marriage benefit, the well-established notion that married people are, over all, far healthier and live longer than the unmarried. But increasingly, researchers are trying to understand the more nuanced effects of marriage on health. To reap the health benefits of marriage, is it enough to just be married? Or how much does the quality of the marriage, such as the level of support, warmth, negativity or controlling behavior, affect the health of seemingly stable couples?

“Unfortunately, a lot of the research on the benefits of marriage measures relationship quality on this unidimensional scale,” said Wendy C. Birmingham, who led the study, which was published in Annals of Behavioral Medicine. “They look at whether you’re happy or you’re not happy, or you feel supported or you’re not supported. But not all relationships are one-dimensional.”

In a carefully controlled study of 94 heterosexual couples in Salt Lake City, the researchers quizzed each partner privately about the level of positive and negative interactions in their marriage. The couples had been married, on average, for 5.4 years, but the lengths of their marriages ranged from one year to 41 years. About 15 percent had been married for a decade or longer. Both partners were working part-time or full-time, and none had children or anyone else living with them in their homes.

“We wanted to look at the effects as they occurred between the couple, and not because someone else was living in the home,” Dr. Birmingham said.

The researchers asked about the level of positive support the men and women received from their spouses and gave to their spouses when one of them needed advice or understanding. They also asked about the level of negativity between the spouses on a daily basis, or when they were excited or happy about something.

Based on the responses, the researchers determined that 23 percent of the couples were in supportive marriages with low levels of negativity. The remaining 77 percent of couples gave mixed responses, suggesting their marriages were more ambivalent in terms of positive and negative feelings toward each other.

Next, the men and women were given baseline blood pressure readings and wore a blood pressure monitor for one day, from morning to bedtime. After random blood pressure readings during the day, twice each hour, subjects used a Palm Pilot to record exactly what they were doing at the moment the blood pressure was taken — eating, working, resting, interacting with their spouse. They were asked about their mood in general and about their feelings toward their spouse at that moment. To ensure accuracy, respondents had only five minutes after the blood pressure check to fill out the diary; otherwise the data would not be included. (In the end, only 7 percent of the diary records were discarded, fewer than one per participant, suggesting the couples were vigilant about compliance with the study protocol.)

The findings reveal the complex nature of marital relationships and the subtle effect positive and negative moments in a marriage can have on physical health. When the researchers analyzed the blood pressure readings, they found that the men and women in ambivalent relationships consistently posted higher systolic blood pressure readings during a given day. That suggests that one of the well-established benefits of marriage — better cardiovascular health — may not be as robust for couples in ambivalent marriages.

To be sure, the study has its limitations. The couples all were heterosexual, mostly white and from the same city. It is also not clear if the high blood pressure findings shown in the study would eventually lead to poorer health over time.

That said, the conclusion that the health benefits of marriage are dependent on the quality of the relationship has been borne out in other research. For instance, a University of Utah study found that a marital fight that lacked warmth or was controlling in tone could be just as predictive of poor heart health as whether the individual smoked or had high cholesterol. Ohio State University researchers found that wounds heal more slowly when couples have hostile arguments compared with couples who manage conflict without hostility. At the University of Virginia, studies showed that when happy couples held hands, the calming effect on the brain was similar to that caused by pain-relieving drugs. But unhappy couples did not show the same benefit.

Arthur Aron of the Interpersonal Relationships Lab at Stony Brook University in New York, notes that every marriage will inevitably have good and bad qualities. But Dr. Aron, who was not involved in the B.Y.U. study, said the results suggest that it is the unpredictable nature of an ambivalent relationship that may be taking the toll.

“Being sometimes supportive and sometimes not supportive is not the same thing as being moderately supportive all the time,” Dr. Aron said. “Part of the issue may be the unpredictability. When you know someone is not going to be supportive, you acclimatize to that. But if they are sometimes one way and sometimes the other way, it’s much harder.”

James A. Coan, the University of Virginia professor who conducted the hand-holding studies, said couples who find they have an ambivalent relationship should not panic about the study findings, but should feel motivated to work on the relationship and seek counseling before their problems become intractable.

“I think about relationships like the stock market,” he said. “There are bull markets and bear markets in any short period of time, but if you take the long view, the investment almost always pays off.”

Is your marriage ambivalent? Take our quiz to find out.

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