The study published by medical journal, The Lancet looked at figures from 50 countries around the world – rich, poor and in-between – over a 50-year time span.
Premature deaths among both children and teenagers had fallen altogether, it found. But death rates have not been dropping as fast among teenagers and young people. That leaves death rates in this age group are now higher than in young children, reversing a historical trend.
The study found death rates in children aged between one and nine has fallen by between 80 and 93 per cent over the past 50 years. Researchers put the fall down to global success fighting infectious disease.
Violence, suicide and road accidents meanwhile were blamed for the relative rise in deaths of teenagers and young people.
In particular, death rates in young men aged between15 and 24 are now two to three times higher than in boys between the ages of one and four. Most deaths in young people are now due to injury, it said.
"What is clear is that the greatest threats to young peoples' health, outside of living in extreme poverty and in 'hot zones' of infectious disease and war, stem from the behaviours in which young people engage, and the contexts in which they find themselves," the University of Minnesota’s Dr Michael Resnick, who co-wrote the report.
Governments now need to focus "on violent neighbourhoods, extreme impoverishment and lack of access to fundamental resources and services, and the hopelessness that comes from utter lack of prospects and opportunity," he told the BBC.
The researchers now hope their findings will push forward a new global focus on the health and causes of death in teenagers and young people.
Despite the overall improvement in death rates among children, teenagers and young people, about 29,000 children under five – 21 each minute still die every day, mainly from preventable causes.
More than 70 per cent of almost 11 million child deaths every year down to six causes: diarrhoea, malaria, neonatal infection, pneumonia, preterm delivery, or lack of oxygen at birth, according to figures from the United Nations Children’s Fund (Unicef).
Most of these deaths are in the world’s poorest countries. An Ethiopian child is 30 times more likely to die by his or her fifth birthday than a child in Western Europe.