Unwed mothers face poorer health at midlife than do women who have children after marriage, according to a new nationwide study, which appears in the June 2011 issue of the American Sociological Review.

Researchers found that women who had their first child outside of marriage described their health as poorer at age 40 than did other moms.

This is the first U.S. study to document long-term negative health consequences for unwed mothers, and it has major implications for our society, said Kristi Williams, lead author of the study and associate professor of sociology at Ohio State University.

About 40 percent of all births in the United States now occur to unmarried women, compared to less than 10 percent in 1960, Williams said. That suggests there will soon be a population boom in the United States of single mothers suffering middle-aged health problems.

"We are soon going to have a large population of single mothers who are entering midlife, when many health problems just begin to emerge," Williams said. "This is a looming public health crisis that has been pretty much ignored by the public and by policymakers."

Moreover, the study suggests that later marriage does not generally help reverse the negative health consequences of having a first birth outside of marriage. This calls into question the value of government efforts to promote marriage, among low-income, single mothers, at least in terms of their consequences for these women's health.

"It is a tall order to expect that marriage can counteract the cumulative strains of unwed motherhood and their eventual negative impact on health," Williams said.

The study used data from the National Longitudinal Survey of Youth, which has followed a nationally representative sample of nearly 13,000 men and women who were aged 14-22 in 1979. They were interviewed every year through 1994 and every two years since.

In one analysis, Williams and her co-authors used a subset of data from the National Longitudinal Survey of Youth on 3,391 women and a second analysis involved data on 1,150 women. By 2008, they had data on marriages and other unions for a 29-year period, and measures of health and well-being taken when the women were 40.

In general, the results showed that unwed mothers reported poorer health at age 40 than did other mothers. But there were several notable differences between racial and ethnic groups.

Most notably, Hispanic women who had a first child outside marriage did not have the same negative health consequences at age 40 that white and black women did. The researchers suspect that it has to do with the fact that when Hispanic women have a child out of wedlock, it is more likely to occur in a long-term cohabiting relationship that resembles marriage.

Hispanic single mothers may also be a part of larger and more close-knit family networks than single moms from other racial and ethnic groups, which can provide support that protects their health and helps them cope.

Williams said it was beyond the scope of this study to determine why unwed mothers in general had poorer health than others. But other research suggests it may be related to the high levels of stress and the poor economic conditions faced by single moms.

"Research has clearly shown the toll that long-term stress takes on health, and we know that single mothers have a great deal of stress in their lives," Williams said. "Their economic problems only add to the problem."

But if single motherhood is hard on women's health, the answer isn't necessarily getting married, Williams said.

Results showed that for most women, the negative consequences of having a first birth out of wedlock won't be eased by a later marriage or cohabiting union. The one exception, at least in some cases, was marrying the biological father.

Among white and Hispanic women who had a first child outside of marriage, those who married the biological father of their child and remained married to him did have better health at age 40 than did those who didn't have partners. But that advantage did not apply to black women, who have a larger percentage of out-of-wedlock births compared to women of other racial and ethnic groups.

"Marriage to the father of their child tends to help by providing women with economic and social support, but black women are disadvantaged in marriage in both of those respects," Williams said. "Black single mothers are more likely to marry men who have poor economic prospects, in part because decades of poverty have contributed to a shortage of marriageable men."

These results cast doubt on the benefits of government efforts to promote marriage for the health of women most affected by such undertakings, Williams said. Beginning with the 1996 U.S. welfare reform act, federal and state governments have developed programs to promote marriage, particularly among low-income single mothers. These efforts have included public advertising campaigns emphasizing the importance of marriage and programs providing relationship skills training.

"Studies have shown the average benefits of marriage to women in the general population," Williams said. "But this study shows that these benefits don't apply equally to single mothers, at least when it comes to health. They have too much working against them to benefit from marriage in most cases."