On the other hand, even having a supportive social network did not translate into a blood pressure benefit for singles or unhappy married people, according to the study.
"There seem to be some unique health benefits from marriage. It's not just being married that benefits health -- what's really the most protective of health is having a happy marriage," study author Julianne Holt-Lunstad, a psychologist who specializes in relationships and health, said in a prepared statement.
The study included 204 married and 99 single adults who wore portable blood-pressure monitors for 24 hours. The monitors recorded blood pressure at random intervals and provided a total of about 72 readings.
"We wanted to capture participants' blood pressure doing whatever they normally do in everyday life. Getting one or two readings in a clinic is not really representative of the fluctuations that occur throughout the day," Holt-Lunstad said.
Overall, happily married people scored four points lower on the blood pressure readings than single adults. The study also found that blood pressure among married people -- especially those in happy marriages -- dipped more during sleep than in single people.
"Research has shown that people whose blood pressure remains high throughout the night are at much greater risk of cardiovascular problems than people whose blood pressure dips," Holt-Lunstad said.
The study was published in the March 20 issue of the journal Annals of Behavioral Medicine.
The study also found that unhappily married adults have higher blood pressure than both happily married and single adults.
Holt-Lunstad noted that spouses can encourage healthy habits in one another, such as eating a healthy diet and having regular doctor visits. People in happy marriages also have a source of emotional support, she said.