Marriage may not always be as beneficial to health as experts have led us to believe, according to a new study. Researchers made two discoveries that explain why: First, marriage provides less protection against mortality as health deteriorates（恶化）, even though it does seem to benefit those who are in excellent health. Secondly, married people tend to overestimate how healthy they are, compared to others.

"We believe marriage is still good for the health of some people, but it is not equally protective for everyone," said Hui Zheng, lead author of the study and an assistant professor of sociology at The Ohio State University.

"For those who are already in poor health, marriage doesn't seem to provide any extra benefits."

The results generally held true for both men and women. They were also similar for all types of unmarried people, including divorced, widowed and never married, as well as separated people.

Zheng conducted the study with Patricia Thomas of the University of Texas at Austin. Their results appear in the March 2013 issue of the Journal of Health and Social Behavior.

The researchers used data on about 789,000 people who participated in the National Health Interview Survey from 1986 to 2004. In this survey, participants rated their own health on a five-point scale (excellent, very good, good, fair, poor). Zheng and Thomas then used follow-up data to identify the nearly 24,100 people who died between 1986 and 2006.

The self-rated health measure used in this study has been found to be one of the best predictors of whether a person will die in both the short and long term -- even better than doctor diagnosis in some cases, Zheng said.

The researchers used a statistical model to determine how self-rated health, marriage status and other factors related to mortality risk over a three-year period.

Overall, the researchers confirmed the volumes of previous research that has found that, overall, being unmarried -- including never married, separated, divorced and widowed -- significantly increases the risk of death within three years. For example, a never-married person who lists his health as "excellent" is two times more likely to die within three years than a similar married person in excellent health.