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You need to pick your spouse wisely. If you are married, you really need to work at making it a high-quality marriage.

- Study author Julianne Holt-Lunstad, BYU psychology professor

When it comes to blood pressure, it's healthier to be married than single. But it's better to be single than unhappily married.

Those are the results of a Brigham Young University study funded by competing interests: BYU's Family Studies Center, whose mission is to strengthen families, and the San Francisco-based Anthony Marchionne Foundation, which supports research on singles.

The study was published today in the Annals of Behavioral Medicine. Lead author Julianne Holt-Lunstad, a BYU psychology professor, randomly measured blood pressure of 204 married and 99 single men and women over a 24-hour period.

Married adults benefited from a drop of more than 11 points in systolic blood pressure at night compared to 8 points for singles. A reduced amount of so-called "blood pressure dipping" is thought to contribute to organ damage, according to the study.

The finding is in line with other studies showing the health benefits of marriage. But marriage isn't an elixir by itself.

While previous research has compared high-quality marriages to low-quality ones, little has been done to compare health effects of low-quality marriages to being single, Holt-Lunstad said.

She identified low-quality marriages through surveys about adjustment to marriage and satisfaction, and found it was better to be single when it comes to blood pressure.

"You need to pick your spouse wisely," Holt-Lunstad said. "If you are married, you really need to work at making it a high-quality marriage."

Craig Parks, director of the Marchionne Foundation's small-grants program, said the results will help combat the stereotype that being single equals being unhealthy.

"It really continues to feed into this database that's growing that people who are [single for life] are just not automatically at the bottom of the health barrel," he said.

Janice Kiecolt-Glaser, director of the Division of Health Psychology at Ohio State University's College of Medicine, said the findings are "a nice addition" to previous research. "They suggest that being single is better for your health than a bad marriage," Kiecolt-Glaser, who was not involved in the BYU study, said in an e-mail.

The new study found happily married individuals' blood pressure was 4 points lower than single adults. They were also less stressed and depressed.

But being married only seemed to provide a benefit at night. There was no difference among married and single individuals' average 24-hour or waking blood-pressure readings.

Holt-Lunstad wonders if blood pressure during the day is more influenced by external factors while the nighttime drop reflects the benefits of a stable relationship.

She expected to find that single people or unhappily married individuals would benefit from having close friends, co-workers or siblings - that a strong social network would help lower blood pressure. She was surprised to find that didn't happen.

"There does seem to be something a little bit unique about the marital relationship," she said.

* A 2004 study by the Centers for Disease Control and Prevention found that married adults were less likely than other adults to be in fair or poor health and were less likely to smoke, drink heavily or be physically inactive. Other studies have shown a link between high blood pressure and marital problems.

* The new BYU study's findings are potentially limited because the adults studied were predominantly white and, as residents of Utah County, may have been predominantly Mormon.

* Among singles, the BYU study didn't distinguish among those in serious dating relationships or people who chose to be single.