By Lin Taylor

LONDON, June 7 (Thomson Reuters Foundation) — About 115 million boys were married off as children with 1 in 5 wed before they turned 15, according to the first United Nations' study to track the prevalence of child grooms.

The UN children's agency UNICEF analyzed marriage and population data across 82 countries and found the Central African Republic had the highest prevalence of child grooms at 28%, followed by Nicaragua at 19% and Madagascar with 13%.

UNICEF said children married young tended to leave school, have limited economic opportunities, and be more vulnerable to abuse and mental health problems than those who married later.

"Marriage steals childhood," the charity's Executive Director Henrietta Fore said in a statement as the report was released on Friday.

"Child grooms are forced to take on adult responsibilities for which they may not be ready. Early marriage brings early fatherhood, and with it added pressure to provide for a family, cutting short education and job opportunities."

UNICEF said these figures meant that there were now 765 million married boys and girls among the 2.2 billion children globally, but girls were still more likely to wed young, which put them at risk of health issues related to teen pregnancies.

Globally about 1 in every 5 women aged 20 to 24 were married before their 18th birthday, compared to 1 in 30 men, UNICEF said.

Read More: More Than 78,400 Children in the US Were Married Between 2010 and 2014

If all girls finished secondary school, more than 50 million child marriages could be prevented by 2030, children's charity Save the Children said in an October report.

The United Nations has said all countries should end child marriage by 2030 as agreed in the global development goals in 2015.

Almost all countries have a minimum marriage age of 18, but children can still legally wed in places like the United States if they have parental consent or through religious ceremonies, according to data research group World Policy Analysis Center.

(Reporting by Lin Taylor @linnytayls. Editing by Belinda Goldsmith. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's and LGBT+ rights, human trafficking and slavery, property rights, social innovation, resilience and climate change. Visit http://news.trust.org to see more stories).