Death rates among adolescents have overtaken those of young children as increasing numbers of young males are dying through violence or injury while efforts to reduce child mortality are succeeding.
A study of data from 50 countries over the second half of the 20th century found that most deaths of young people were due to incidents such as car accidents or reckless behavior, with violence and suicide also key causes of death.
The findings, published in the Lancet medical journal on Tuesday, show the reversal of an historical trend and are partly a reflection of success in reducing death rates among very young children, the researchers said.
But the strong international focus on reducing infant and child mortality has not been matched by similar efforts in older groups, they said, even though more than two-fifths of the world's population are in the five to 24 years age group.
"These trends are likely to continue because mortality in children younger than five years is expected to decline further, and injury-related mortality is expected to increase in the next 25 years," said Russell Viner from the University College London institute of child health, who led the study.
Commenting on the findings, Michael Resnick of the University of Minnesota in the United States, who was not involved in the study, said they showed how "the profound health and social changes that have accompanied economic development and urbanization are particularly toxic for young people in both high-income and low-income settings."
A study in 2009 by World Health Organization (WHO)-supported researchers found that 40 percent of adolescent deaths were due to injuries and violence.
Against this background, Resnick said breakthroughs in medical progress and service delivery were not enough to counter health threats faced by young people because of the major role played by factors such as socioeconomic conditions, opportunity and access to education.
Viner's team used the WHO mortality database to analyze data for 50 rich and poor nations between 1955 and 2004. They looked at patterns of mortality by age group, sex and cause of death -- divided into infectious diseases, chronic diseases and injury.
To find changes in mortality, they calculated death rates averaged over three five-year periods -- 1955 to 1959, 1978 to 1982, and 2000 to 2004.
Findings showed that in the 1950s, mortality in the one to four age group far exceeded that of all other age groups in all regions studied. But in the 50 years up to 2004, death rates in children aged one to nine fell by 80 to 93 percent, mostly due to reductions in deaths from infectious disease.
In contrast, declines in death rates in those aged 15 to 24 years were only about half that in children, largely because of increases in injury-related deaths, particularly in young men.
The researchers found that by the start of the 21st century, injuries -- such as in incidents like car crashes and street or gang violence -- were responsible for 70 to 75 percent of all deaths in young men aged 10 to 24 in all the regions studied.
By 2004, suicide and violence were responsible for between a quarter and a third of deaths in young men aged 10 to 24 years, and death rates in young men aged 15 to 24 are now two to three times higher than in boys aged one to four, they said.