Marriage may be nearly universal, but does it still matter? Reliable contraception has lowered the intimacy stakes, and women have won some economic and political equality with men, so perhaps marriage has become optional instead of necessary. However, there are some reasons to doubt the benefits of a post-nuptial society. Married people tend to be happier and healthier than the divorced or the never-married.

The previous studies have been subject to some reasonable criticisms. After all, how can you be sure that happy and healthy people aren’t more likely to marry in the first place? Do the benefits of marriage outweigh the costs? A clear-sighted assessment of the choice to marry must factor in all marriage risks, including preconditions, divorce, and the goods it grants.

In a new study in the Global Epidemiology journal, researchers hoped to address these critiques, examining 11,830 American nurses, all women, who were originally never married and comparing those who married between 1989 and 1993 to those who remained unmarried. They assessed how their lives turned out on a wide variety of essential outcomes, including health, longevity, and psychological well-being, after 25 years.

In most cases, researchers controlled the nurses’ health and well-being in 1989, before marriage, and numerous other factors like socioeconomic status, race and age. This control helped researchers rule out the possibility that, for example, happiness predicted marriage instead of being indicated by it, or some hidden factor might predict marriage and happiness.

The assessment found that women who got married in the original time frame, including those who ultimately divorced, had a 35 percent lower risk of death for any reason than those who didn’t marry in that time frame. Married women also had a lower risk of cardiovascular disease, less loneliness and depression, and were more optimistic and happier. They also had a greater sense of hope and purpose.

Researchers also assessed the effects of staying married versus getting divorced. Divorce was linked with worse health and well-being among the women who were married at the beginning of the study, including increased loneliness and depression and lower levels of social interaction. There was also less substantial evidence that divorced women had a 19 percent higher risk of death for any reason over the 25 years of follow-up than women who stayed married.

Given how many factors influence health and well-being, marriage could reduce 25-year mortality by more than a third, and that divorce could increase it by nearly a fifth, indicating how important it remains even for modern life.

The causes of marriage’s marginalization are complex, including cultural shifts and economic constraints, particularly the declining earning power of less-educated men, which substantially reduces their marriage prospects even today. It is clear, however, that many of us now view marriage not as an essential setting for socializing sex and raising children but as a dispensable luxury.

The study’s findings, added to an already extensive literature showing the value of marriage, should serve as a wake-up call for a society in significant denial about this crucial element of flourishing.