The biggest health threats facing adolescents and young people have largely been ignored for the last 30 years, leading to a negative impact on their well-being and mortality, a report has found. Although people aged between 10 and 24 represent more than a quarter of the world's population, there has not been as much effort to reduce mortality and the disease burden as there has been in other age groups – the under-fives, in particular.

These are the conclusions of a Lancet commission on Adolescent Health, investigating how preventable diseases, infections, mental disorders and unsafe sex are affecting adolescents around the world.

Bringing together experts from 14 countries as well as four academic institutions, the report finds that causes of deaths and most common diseases diagnosed in young people have not changed much since 1990 – signs that no real strategies have been implemented to address the issue.

Additionally, some risk factors of ill health have become more important – unsafe sex, in particular.

Last year, the World Health Organization came to similar conclusions, urging countries to promote healthcare among people in this important age group.

Road accidents, mental health and unsafe sex

Because adolescence and early adulthood are considered to be the healthiest time in people's lives, there has traditionally been less investment in their health needs. This is in sharp contrast with infants and children under the age of five, whose mortality rates have been cut by half since 1990.

Mortality has decreased at much slower rates in people aged 10-24. Depression, road accidents, HIV and drowning caused a quarter of deaths in that age group in 2013. There are contrasts between boys and girls: the former are more likely to die in traffic accidents, while the latter are more affected by mental disorders that can lead to self-harm and death. These causes of mortality have been affecting teenagers since 1990 without much change.

Mental health, iron deficiency and alcohol consumption remain significant factors of ill health, but one of the report's main findings is the increase in unsafe sex. It is actually the fastest-growing health-risk factor for young people, moving a placing of 13 to the second-biggest problem. Unwanted pregnancies, HIV and other sexually transmitted diseases are among the most frequent issues.

What steps for the future?

The commission has come up with a series of recommendations to make adolescent health a priority. With 1.8 billion people aged between 10 and 24, this is the biggest generation of adolescents in history - a figure which gives a good idea of the scale of the challenge.

Among the most important steps to reduce death and disease rates are the need to expand access to free secondary education, to empower and protect adolescents through the law (such as guaranteeing the minimum age for marriage remains at 18), and continue gathering better evidence for action, particularly around mental health and violence.

"The single-best investment we can make is guaranteeing access to free, quality secondary education," concluded Professor Patton, the commission's lead author. "Every year of education beyond the age 12 is associated with fewer births for adolescent girls and fewer adolescent deaths for boys and girls. A healthy, educated workforce has the potential to shape a country's economic prospects."