NEW YORK - Child brides more often face psychiatric disorders than women who marry after they turn 18, according to a study that is the first to try and gauge the mental toll of child marriage, which is already tied to several health problems.

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 the report, published in Pediatrics, said that the United States also has a fair share of underage brides.

Based on a government survey from 2001 and 2002, the study estimated that as many as nine percent of US women took their vows when they were under the age of 18.    

"Child marriage increases the risk of lifetime and current psychiatric disorders in the United States," wrote Yann Le Stat, at the French National Institute of Health and Medical Research in Paris, and colleagues.

"Support for psychiatric vulnerabilities among women married in childhood is required."

About 9.4 million women in the United States married at 16 or younger, and 1.7 million were no older than 15, according to the government survey.

Blacks and Native Americans were more likely to be child brides than whites, Le Strat and his team said.  

Face-to-face interviews with nearly 25,000 women who were at least 18 showed that 53 percent of those who had been child brides had some psychiatric disorder, such as depression or anxiety.

That compared to 49 percent of women who married as adults.

Women who married under the age of 18 were also more likely to be diagnoses as "nicotine dependent" and with "anti-social personality disorder."

The researchers cautioned that their findings don't prove that marrying as a child will necessarily lead to mental illness.

Yet most women had been married before they developed mental problems, and the findings couldn't entirely be written off as due to the differences in household incomes, education and other social factors, they added.

All but one US state require couples to be at least 18 years old to be married, but with parental consent, couples can marry at 16 in most states. Under some circumstances, however, marriage age can be as low as 15 in Hawaii and Missouri.