Those who have never married have a 58% higher risk of an earlier death, compared with a married reference group, found Robert Kaplan, Ph.D., of the University of California at Los Angeles and Richard Kronick, Ph.D., of UC San Diego.
Strikingly, the 58% never-married penalty was also higher than the 27% combined death rates for those who were separated or divorced and the 39% rate for widowed persons. they reported in the August issue of the Journal of Epidemiology and Community Health.
Drs. Kaplan and Kronick suggested that those who have never married may require special attention. Their risks, they said, rival the risks of having increased blood pressure or high cholesterol. "Our data suggest that being never married deserves a separate category and more research attention," they wrote.
The findings were based on the U.S. 1989 national health interview survey and 1997 national death certification data. Analysis of marital status and mortality among 67,000 adults found that 5,876 (8.8 %) had died before 1997 while 61,123 (91.2%) were known to be alive.
In 1989, 47.7 % were married and almost 10% were widowed. About 16% were divorced or separated, 5% were living with a partner (they were excluded from the study), and 20% had never been married, the researchers wrote.
As expected, older age and poor health were the strongest predictors of death by 1997 whereas a surviving marriage, strongly associated with a longer life, was used as the reference group.
Controlling for age, health status, and demographic and socioeconomic characteristics, the researchers found that the death rate for people who never married was 58% higher than that for the married reference group (OR 1.58, CI 1.39-1.78).
For the youngest age group (19 to 44), the main causes of early death among never-married adults were infectious disease (presumably HIV) and so-called external causes.
Among middle-aged and older never-married men and women, the predominant causes were cardiovascular and other chronic diseases, the researchers reported. Actually there were only two causes, cancer and pulmonary disease, for which being single was not a risk factor relative to being married, they said.
The never-married penalty was seen for both sexes, and was significantly stronger for young men than for young women.
Never-married men, ages 19 to 44, were twice as likely to die as married men of the same age (OR 2.12, CI 1.68 -2.67), although the risk declined with increasing age to zero after age 65.
Among never-married women, for whom the risk while young (OR 1.64) was lower than the men's, the risks did not decline with increasing age. Thus by age 65, the women's risk (OR 1.48) had overtaken the men's.
Risky behavior could not explain the difference, Drs. Kaplan and Kronick said, because the members of the unmarried group were only slightly more likely to smoke than their married counterparts, and they were less likely to drink alcohol regularly. They also exercised slightly more and were less likely to be overweight.
One frequently offered explanation, namely that sick people require greater support, suggests that the never-married penalty would be stronger for those in poorer health. However, those in excellent or very good health were at least five times likelier to die (odds ratio 1.88, CI 1.53-2.32) than those in fair health (odds ratio 1.36, CI 1.06-1.74), the investigators said.
Although most authors cite being divorced/separated or widowed as risks, the current study suggests that never being married carried a greater mortality risk from all causes, from external causes, and from infectious diseases. Furthermore, they said, the single life was equivalent to being widowed for risk of death from cardiovascular disease.
It is difficult to assess the causal effect of marital status from these observational data, Drs. Kaplan and Kronick wrote.
One possible explanation, they said, lies with the impact of social isolation, although the data suggest that the effect of non-marriage is stronger than that of being divorced or widowed. Accumulated evidence suggests that social isolation, which is not restricted to the elderly, increases the risk of premature death, but varies at different stages of the life cycle.
It is possible that marriage is a rough proxy for social connectedness, they added. "We suggest that having never married may be associated with more severe isolation because it is associated with greater isolation from children and other family," they wrote.
As for the role of illness, the researchers said that its effect is hard to interpret. Clearly the findings challenge the belief that social isolation is linked to heart disease, since overall the findings underscore the impact of all-cause mortality.
Among the study's limitations, the authors noted the fact that the data were limited to baseline information and mortality follow-up. For this reason they were unable to assess other variables such as changes in health or in marital status.