Child brides more often face psychiatric disorders than women who marry after they turn 18, researchers have found.
Their work is the first to try to gauge the mental toll of child marriage, which has already been tied to several health problems, such as pregnancy complications and an increased risk of sexually transmitted infections.
So far, most research has focused on child marriages in low- and middle-income nations in Africa and Asia, where it is often rampant.
But according to the new report, the U.S. also has its fair share of underage brides.
Based on a government survey from 2001 and 2002, it estimates that as many as nine percent of American women took their vows as kids. About 9.4 million women were married at 16 or younger, and 1.7 million were no older than 15.
All but one U.S. state require couples to be at least 18 years old to be married. With parental consent, however, marriage age is only 16 in most states, and under some circumstances may be as low as 15 in Hawaii and Missouri.
Blacks and Native Americans were more likely to be child brides than whites, Dr. Yann Le Strat, of the French National Institute of Health and Medical Research in Paris, and colleagues report in the journal Pediatrics.
Although the rate of child marriage seems to be on the decline, they say, "support for psychiatric vulnerabilities of women married as children is required."
Face-to-face interviews with nearly 25,000 women who were at least 18 revealed that 53 percent of those who had been child brides had some psychiatric disorder, such as depression or anxiety.
Of the women who married as adults, that figure was 49 percent.
Former child brides were also more likely to be diagnosed as "nicotine dependent" and with "anti-social personality disorder."
The findings don't prove that marrying as a child will necessarily lead to mental illness, the French team cautions.
Yet most women had been married before they developed mental problems, and the findings couldn't be entirely chalked up to differences in household incomes, education and other social factors.