The friend who both pleases and vexes you may be bad for your health. A research collaboration between Brigham Young University and the University of Utah found that mixed-feeling friendships may not let you relax or provide the social support you need during stressful times.

The study is being published today in the Annals of Behavioral Medicine. The researchers found that "unpredictable and ambivalent friendships" raise blood pressure, possibly because they are a source of stress, while more positive friendships help you deal with stress. Next, they hope to study whether those ambivalent friendships can contribute to cardiovascular problems such as high blood pressure or clogged arteries.

That's important information, according to Julianne Holt-Lunstad, an assistant professor of psychology at BYU, because about half of most people's relationships are somewhat ambivalent.

"Our friends can be our best allies and our harshest critics," John Cacioppo, president of the Association for Psychological Science and a University of Chicago professor who was not involved in the research, was quoted in a release about the research. "This research demonstrates that a more sophisticated conceptualization of our social relationships provides richer information about their impact on our health."

The study confirmed an earlier finding that blood pressure is higher when people are with their mixed-feeling friends than with people they either really like or dislike.

For this study, the researchers — led by Holt-Lunstad and the U. psychology department's Bert Uchino, associate professor, and Timothy W. Smith, professor — got about 100 people to each list 10 friends, then answer questions about them, ranging from how long they've known each other and how often they see them to how helpful that person is during times of stress or how supportive, among other questions. Based on that information, the researchers rated the friendships as supportive or ambivalent

They were looking for mid-ground ambivalence, friends who score at least a three out of six in terms of positive feeling but who also are somewhat upsetting.

Then they specified which friend to bring in for the study — either supportive or conflicted — without saying why.

The two were asked some questions in the lab, mostly to get them used to the setting, since it's not where friends normally hang out, Holt-Lunstad said. Then they were separated by a curtain and told to relax and not talk so that the researchers could establish baseline cardiovascular measures.

After chatting about something mundane — what do you do in a typical day, for example — the participant was asked to disclose a moderate-intensity experience that researchers had selected from the participant's list of five positive or five negative recent experiences.

"We were trying to more or less simulate the types of conversations you might have with a friend in the real world," Holt-Lunstad said.

Blood pressure rose across the board for those who brought in ambivalent friends, and not just when discussing a negative experience, although that's when it was highest.

They also measured the friend's blood pressure, but haven't analyzed that yet to see what effect the interaction has on the friend.

Holt-Lunstad didn't know who was assigned to bring in a supportive friend and who was told to bring a mixed-feeling friend. But she said she could usually tell just by watching their blood pressure and pulse.

She said they were surprised that participants who shared good news with an ambivalent friend didn't get the physical benefits that normally occur. Instead, they seemed to "disengage" from the discussion of their own good news.

Holt-Lunstad said the findings have suggested future research, including whether avoiding specific topics that are a source of conflict will reduce stress.

They also plan to study the extent to which various barriers influence maintenance of the ambivalent relationships, including social ties, family relationships or the fact that you live next door to or work with each other.

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