They should be the healthiest people on the planet, the "almost grown ups" still in the bloom of youth and full of dreams for the future. But today's adolescents are instead a troubled generation.
Far from being the healthiest time of life, adolescence is instead a period of maximum risk and maximum vulnerability according to scientists, as still growing bodies and undeveloped minds hurl themselves into experimentation with drink, drugs and sex. They are targeted by the mass marketing of unhealthy products and lifestyles – tobacco, alcohol, junk food – which doctors compare to an infectious disease epidemic. And evidence shows British teenagers are among those exposed to the greatest threats.
In a series of papers published in The Lancet, scientists describe how new research has changed our understanding of adolescence which was thought to start with the physical changes to the body around puberty and to be completed in the late teens. Now researchers believe the brain is not fully developed until at least 24.
While puberty catapults adolescents into a period of risky behaviour powered by their raging hormones, their brains are ill-equipped to exert control and vulnerable to the effects of activities such as drinking and drug taking. Scientists say the adolescent brain is handicapped in the rational assessment of risk and prone to "hot cognitions" – decisions influenced by exciting or stressful conditions which adults are better able to resist.
The modern teenager is taking longer than ever to grow up and, despite its legal significance, 18 is no longer regarded as the start of adulthood. Fifty years ago people married and started families at this age. Today over three times more young people are in further education and most spend years in work before marrying and settling down.
The single biggest cause of deaths in adolescence is injury as a result of accident, often triggered by unnecessary or excessive risk taking. Better scientific understanding of the maturation of the brain has underpinned policy decisions such the limit imposed on the number of adolescent passengers permitted in a car with a young driver, in the US and Canada. Yet despite its significance for lifelong health, adolescence has been neglected in scientific and medical research.
British teenagers score among the worst on measures of adolescent health behaviour. England ranked fourth out of 40 high income countries for the proportion of 13-year-olds who had ever been drunk. Wales was fifth and Scotland eighth.
One in five adolescents indulges in binge drinking at least weekly in high income countries and Britain was again among the worst. The UK also has high rates of sexual activity in early adolescence (aged 13-15), ranked third behind Denmark and Iceland in girls. Despite a recent decline, Britain still has one of the highest rates of teenage pregnancy in western Europe. The Health Survey for England reported last November that a quarter of girls had sex before the age of 16, triggering claims about the "pornification" of British culture. US researchers warned last year that heavy drinking during the teenage years can affect the brain, particularly the development of spatial memory.
For the 1.8 billion adolescents in the world today – comprising more than a quarter of the world's population – families remain the key factor in their healthy development.
Adolescents who feel connected to their family smoke fewer cigarettes, drink less alcohol, use less marijuana, start sex later and are less likely to be involved in violence. Parents who know about and are involved in their children's lives are less likely to have problem adolescents.
Research suggests infancy and early adolescence represent two clusters of risk. The abused or neglected child struggles to learn in primary school, is rejected by its peers and then progresses to drinking, smoking, drug taking, early sexual experience, violence and pregnancy, leading to the premature end of schooling.
More than half of those who develop disorders such as alcohol misuse and anti-social personality disorder are diagnosed by the age of 25, highlighting the vulnerability of the adolescent years.
In its editorial, The Lancet says four steps are needed to improve the lives of adolescents – These are: international comparisons of their behaviour, goals for their healthy development, preventive measures to reduce obesity, alcohol and drug abuse, and monitoring of their progress.
"Young people are our future assets," it states. "They provide energy, innovation, productivity and progress ...Adolescent health [should be] an equal concern alongside existing health priorities in the world."