According to the study, marital strain is a key source of stress, which can affect one's immune system. But unhappiness also affects people's opinion of how healthy they are.
The researchers questioned 1,049 married people and asked them to rate, on a five-point scale, various aspects of their married life, such as how satisfied they were with their marriage, how often they argued and whether their spouse was willing to listen to their problems. The scientists then compared those answers to other responses in which the couples described aspects of their health.
The answers were compared with the participants' responses reflecting how they describe their health.
The conclusion:
The married do exhibit better health than the unmarried but it is not the case that any marriage is better than no marriage at all when it comes to health benefits. The quality of relationships is also linked to health.
So, are you risking your health if you remain in a bad marriage? Not necessarily. After all, marriage is, overall, beneficial to people, helping them to live longer and more prosperous lives, etc. Instead of seeking a divorce, the study’s authors suggest that couples who are in bad marriages try to identify their difficulties and improve their relationships.
From my own personal experience in dealing with couples, I'm convinced that there is a direct relationship between both physical and mental health and someone's relationships, married or not. Even if marriage has benefits, it would be too broad an endorsement of marriage to suggest it is married people alone who are healthier.
In my experience it is the quality of the relationship which is important. Any couple in a positive relationship, married or not, can expect to be healthier.