"A person's heart condition seems to be influenced by negative intimate relationships," the researchers write. "We showed that the negative aspects of close relationships...are associated with coronary heart disease."
Says lead author Roberto De Vogli, an epidemiologist at University College London: "Other research has shown more social connections can mean a healthier life -- the "protective effect" -- but few studies have looked at how close friendships or marriages affect health.
"We found the effect is there not only for married people but also for unmarried people who have negative relationships with close friends", de Vogli adds.
The researchers studied civil servants who completed questionnaires about negative aspects of their relationships (which included a spouse or close friend between 1989 and 1990 or between 1985 and 1988.
The questions probed whether people had emotional support, a chance to talk with someone about problems or whether they could count on a partner or close friend for something as simple as a ride to the grocery store.
The team did a follow-up over a 12-year period and found that people who reported that arguments, criticism and other types of conflict were common had a 34 percent greater risk of heart attacks or chest pain.
When the researchers weeded out risk factors such as obesity, smoking, drinking and family history, the chance of a heart attack was still 23 percent higher, De Vogli informs.
"If you have good people around it is good for your health.
"If you have negative people around it is much worse for your health", he warns.
At the same time, the study did not look at whether a bad relationship played a role in the severity of a heart attack.
"It seems clear from this analysis that no matter if positive aspects of social relationships are having a significant protective effect, the negative impact seems far stronger, as people continually replay negative experiences", conclude the researchers. This they suggest is because it can activate emotional responses, including depression or hostility, in turn boosting heart disease risk.
The researchers found that this association held for both men and women and for those in higher and lower social positions. They also found that those in lower-grade jobs were more likely to have negative relationships. In addition, negative close relationships were less likely in people who were never married.