George and I are often asked, why focus on adolescent health? Adolescents are healthy, aren't they? And in any case, there's not much you can do with adolescents. They're risk takers, they're difficult. They don't listen to adults. It's a whole lot simpler to just deal with things once they've grown up. These sorts of attitudes are some of the reasons why globally, adolescent health has not received the attention it deserves. And why Richard Horton, the editor of the Lancet Medical Journal, was able to say a couple of years ago that adolescents are the most pervasively neglected group, in global health. In saying this he recognised the importance of investing in adolescents. This course is designed to provide answers to the question of why adolescent health matters. To outline new thinking about adolescence as a critical period within the life course. And to think about the sorts of investments and actions that will promote the health of today's adolescents. >> So, how do we think about health of adolescents? It's certainly true that on some indicators adolescence is a healthy time. Through much of human history there's been a low point in mortality across the life course. And adolescents are stronger, faster, fitter, and smarter than at any other point in the life course. But it's now clear that in many countries, that the health burden across the life course is changing. And that adolescents are affected by a unique set of health problems that differs markedly from those of other ages. Population health change is one reason. Mortality rates have fallen sharply in younger children in high and middle income countries compared to those in adolescents and young adults. This figure shows estimates of all-cause mortalities, that is death rates for 1 to 4 year olds from 1980 and 2013. Over this 33 year period mortality in 1 to 4 year olds fell to around a quarter of the 1980 levels. In contrast, while the mortality in 20 to 24 year olds has fallen, this has been turning around 60% of 1980 levels. As a result, mortality in males in a growing number of high and middle income countries is now greater in older adolescence and young adults than in one to four year olds. There have been other shifts as well. With the declines in many infectious diseases, and problems of early childhood, the global focus has shifted to noncommunicable diseases. From a life course perspective, noncommunicable diseases that manifest later in life. Are influenced by events, exposures and behaviours occurring in adolescence. Cancer, diabetes and heart disease in adulthood commonly stem from risks such as tobacco and alcohol use. Physical inactivity, poor diet and obesity that begin in adolescence. A broad range of health problems affect adolescents and young adults. These include some that also occur at other times of life. Including sexual and reproductive health problems and HIV, infectious diseases and chronic physical health disorders. But are there are a unique set of problems related to emotion and emotional control that characterise adolescent health. This is the age in which mental disorders commonly begin, and have a greater impact during this time of life than at any other. Problems with substance use typically emerge during the adolescent and young adult years. Injuries, both intentional and unintentional rise in these years. Intentional injuries include the problems of suicide, and homicide. And the onset of many health risks including those with sexual reproductive health, are also related to emotion and emotional control. >> So why does this matter? There are a set of health problems, as George has outlined, that affect adolescents, that we have largely neglected. And that have not seen the gains that have occurred in other age groups. These conditions are the focus of this course. But adolescence also provides a foundation for health across the life course. The social, cultural, emotional, educational, and economic foundations established during adolescence, reaps benefits in the decades that follow. Conversely, health risks that begin in adolescence amplify over time, to have major consequences for later life. You will gain an understanding of how this happens during this course. And thirdly, often forgotten, adolescents are the next generation to parent. Without good health, their capacity to successfully provide a healthy start to life for the next generation is diminished. Poor nutrition, mental health problems, substance use, and infectious diseases, including HIV during adolescence and young adulthood. Have the potential to compromise fetal development, but also can greatly effect an individual's capacity to parent that child once it is born. The global community is increasingly aware of the opportunities of investing in adolescence, with some amazing developments in the past year. The sustainable development goals cannot be achieved without addressing adolescents. And the new global strategy for women's, children's and adolescent's health is the first global strategy to explicitly address adolescent health and well being. Much of this course is informed by our work leading two previous series on adolescent health for the Lancet Medical Journal in 2007, and 2012. Together with some of the thinking that went into the recent Lancet Commission on Adolescent Health and Wellbeing, published in May, 2016, which we have made available to you online together with the two previously Lancet series. We think this is an incredibly exciting time to be learning about adolescent health. And we have every confidence, by the end of this course you'll share our excitement.