People who never marry are far more likely to die prematurely than those who get hitched or divorced, say US researchers.
Married couples lived longer
Bachelors aged between 19 and 44 were more than twice as likely to die as their married male peers.
The authors of the study in the Journal of Epidemiology and Health say loneliness is the killer rather than alcohol or cigarettes.
Their work looked at data on 67,000 Americans between 1989 and 1997.
Single people were only slightly more likely to smoke than marrieds and were less likely to drink regularly.
They also exercised more and were less overweight.
Dr Robert Kaplan and colleague Richard Kronick, from the University of California, Los Angeles, believe that people who never marry are less likely to have a good social support network and become isolated, which, in turn, knocks years off their lives.
In 1989, almost one in two of the people they studied were married, and almost one in 10 were widowed. About 12% were divorced and 3% were separated. Of the remainder, 5% were cohabiting, and one in five had never been married.
Although older age and poor health were the strongest predictors of death by 1997, surviving marriage was also strongly associated with a longer life.
Those who had never married were at greater risk than those who were separated or divorced.
Indeed, the risks of being never married, in terms of odds, rival the risks of having increased blood pressure or high cholesterol.
Never marrieds were 58% more likely to have died than peers who were married and living with their spouse in 1989.
Those who had been widowed were almost 40% more likely to die, and those who had been divorced or separated were 27% more likely to die.
The risk among the never marrieds was larger for those in very good or excellent health, and smallest for those in poor health, and it was greater among bachelors than spinsters.
For the younger singletons, the primary causes of death were infectious disease and accidents, homicides and suicides. Among the middle aged and elderly unmarrieds, the main causes were cardiovascular and chronic diseases.
But the researchers believe it is social isolation that underpins the premature death risk.
The researchers said: "Accumulated evidence suggests that social isolation increases the risk of premature death.
"Having never been married may be associated with more severe isolation because it is associated with greater isolation from children and other family."
Alternatively, it might be that people who have underlying illnesses that threaten their health and shorten their life expectancy are deemed less suitable as marriage material.
Also, many of the never married men in the study died from infectious disease, most likely HIV, note the authors.