"Keep your friends close and your enemies close" is a saying that may not be the best advice for people who are aged 50 and older, according to a recent study.

Researchers from Carnegie Mellon University found that unpleasant or demanding interpersonal encounters increase hypertension risk among older adults.

 Hypertension affects an estimated 65 million Americans and is a major contributor to cardiovascular disease, the leading cause of death in the United States.

"This demonstrates how important social networks are as we age - constructing strong, positive relationships are beneficial to prolonged health," Cohen, the Robert E. Doherty University Professor of Psychology in the Dietrich College of Humanities and Social Sciences, said in a statement.

For the study, researchers used data from the Health and Retirement Study, a multi-year survey of more than 1,500 healthy adults aged 50 and older. In 2006, the frequency of negative interactions - exchanges or behaviors that involved excessive demands, criticism, disappointment or other unpleasantness - with their partners, children, other family members and friends was assessed by questionnaire. Blood pressure was measured at this assessment as well as four years later.

Researchers found that each increase in the total average negative social interaction score was associated with a 38 percent increased chance of developing hypertension over the four-year period. Younger older adults - those aged 51 to 64 - were also more affected than those 65 or older.

They also observed sex differences in their findings. While negative interactions predicted hypertension risk among women, these interactions were not related to hypertension risk among men.

"There is a body of evidence in social psychology research suggesting that women care more about and pay more attention to the quality of their relationships," Rodlescia Sneed, researcher and a Ph.D. candidate in psychology, said in a statement. "Our findings suggest that women are particularly sensitive to negative interactions, which is consistent with this previous work."

The findings were recently published in the American Psychological Association's journal Health Psychology.