Today’s generation of young people is, relative to other age groups, the largest in history. With a population of 1.8 billion, 10-24-year-olds now comprise over a quarter of the global population. This large increase in the youth population arises from improved infant and child survival following dramatic improvements over the past 50 years in maternal antenatal care, acute childhood illness and malnutrition. Nearly 90 percent live in LMICs where they may comprise more than a third of the population. 

Adolescents have been a major focus in recent global approaches to sexual and reproductive health. A life-course perspective also places adolescents centrally in other health agendas including the prevention of non-communicable diseases, mental disorders and injuries [1]. A cluster of health risk behaviours and states that largely start in adolescence (tobacco, alcohol, obesity, physical inactivity) are potential drivers of future non-communicable diseases in adults [2]. This adolescent contribution to dis- ease burden in those over 60 years old includes high blood pressure, cholesterol and glucose (29 percent); tobacco use (10 percent); physical inactivity (7 percent); and overweight and obesity (7 percent) [3]. A range of global factors has come into play in shaping the health of young people. Perhaps the most immediate effect is the widespread dissemination of values and lifestyles that are potentially damaging to health. Tobacco use, alcohol and other substance use, physical inactivity and obesity have spread rapidly to many LMICs in the last two decades. Indeed rates of adolescent tobacco use have diminished in many high-income countries whereas elsewhere rates are escalating rapidly. 

In comparison to younger children, adolescents have seen fewer health gains. In a study of 50 countries with longitudinal data, the mortality of children had declined by over 80 percent in the last 50 years. In contrast, mortality among adolescents had improved only marginally and there has been a reversal of historical mortality patterns in which early childhood mortality exceeds adolescent deaths. Over that time causes of death in adolescents have changed with a fall in infectious deaths in most high- and middle-income countries and a rise in deaths due to injuries, that now account for around 40 percent of all adolescent deaths globally. Causes of injury death include suicide, motor vehicle injury and homicide, with a major difference in patterns and rates of death in different parts of the world. In contrast, in low-income countries in sub-Saharan Africa and southern Asia infectious dis- eases, including HIV, tuberculosis, malaria and maternal causes remain major contributors to death in young people. Moreover, as recently stated by Capua et al. [4], ‘Coverage rates for the adolescent vaccinations continue to lag behind those of the child- hood vaccinations, despite their importance’, even in high-income countries. 

Adolescents need both boosters and new vaccines such as the one against Human Papilloma Virus (HPV). 

Young people bear a substantial disease burden in all regions of the world, both in terms of years of life lost and years of life lost due to disability. Overall they account for over 15 percent of the total disability-adjusted life year toll for all age groups and are the only age group where disease bur- den is higher in women than men. Africa has the highest regional rate of disease burden for those aged 10-24, 2.5 times greater than in high-income countries that have the lowest. The major global causes of disease for those aged 10-24 are neuropsychiatric conditions for both sexes, injuries in males and maternal conditions in females. 

We now also recognize ways in which the health of adolescent girls affects the health of the next generation. The influences range from viral infections such as rubella and HIV, maternal malnutrition and micronutrient deficiency, obesity and gestational diabetes and health risks associated with alcohol, tobacco and illicit and psychotropic drugs use [5]. 

Prevention and Health Promotion 

Adolescent-onset behavioural problems implicated in non-communicable diseases include unsafe driving, mental health, violence, alcohol, tobacco and drug misuse, as well as unsafe sex and teen pregnancy [6]. These health risks are all largely preventable. Over the last 40 years the integration of life course research with prevention trials and community epidemiology has offered a new way forwards in adolescent health. This prevention science framework posits that to prevent the onset of a problem, one must change the factors that predict it [7]. Such factors are commonly termed risk and protective factors and include those from an individual’s family, school and peer contexts as well as individual factors. Risk factors increase the likelihood of problems and protective factors either directly decrease the likelihood of problems or mediate or moderate exposure to risk. There is a good deal of commonality in risk factors across problem behaviours, suggesting that prevention programmes that seek to reduce, for example, family management problems or academic failure are likely to prevent multiple problems despite the fact that the programmes themselves may be focused on single problems such as conduct problems or academic success. 

Although there has been less research on protective factors, longitudinal, prospective studies have identified seven factors that promote positive social development and reduce behaviour problems, including individual factors: high intelligence; resilient temperament; social, emotional and cognitive competence; and environmental factors: opportunities for prosocial involvement; recognition for positive involvement; bonding; and healthy beliefs and standards for behaviour [8]. 

The Gatehouse Project is a primary prevention programme which includes both institutional and individual-focused com-ponents to promote the emotional and behavioural well-being of young people in secondary schools. Using a school-based cluster randomized controlled trial, it has shown effectiveness on behaviours such as substance use by young people, with a 3-5 percent risk difference between intervention and control students for any drinking, any and regular smoking and friends’ alcohol and tobacco use across the three waves of follow-up [9]. Nurse-Family Partnership (NFP) is a programme in which trained, registered nurses provide low-income, single, first-time mothers with biweekly structured visits during pregnancy and for 2 years post birth. Nurses share information on how mothers can reduce their use of alcohol, tobacco and other drugs during pregnancy; improve their prenatal health and diet; sensitively and responsibly care for their infants; achieve their own education and occupational goals; avoid unwanted future pregnancies; and access community services. The programme has been demonstrated in controlled trials to reduce the mother’s reliance on public welfare, the number of subsequent births were reduced by 43 percent, verified reports of child abuse and neglect decreased and mothers increased their workforce participation. Children at age 15 have been shown to have fewer arrests and less alcohol use and fewer lifetime sexual partners compared to those not receiving services [10]. 

Strengthening Families Programme for Parents and Youth 10-14 

The programme targets family, peer and individual risk and protective factors, including parent communication and child management skills; children’s social skills, stress management and ability to refuse peer drug offers; and parent/child conflict resolution and bonding. Across multiple studies conducted in rural communities in the United States the programme has been shown to reduce substance use and delinquency up to 5 years post intervention for participants versus control group members [11]. 

Conditional Cash Transfer (CCT) Programmes provide payments that come with conditions. Examples include payment of school fees and supplemental cash to poor parents with the condition that they send their child to school. Trials in Malawi and Kenya found reduced self-reported sexual activity, pregnancy and marriage in one or both countries and girls and young women who received the CCTs were 15 percent less likely to drop out of school compared to controls [12].

Unplugged is a 12-hour, teacher-led alcohol, tobacco and other drug use prevention programme for early secondary school students. Lessons target peer influence and societal risks and aim to improve students’ goal-setting, decision-making and drug refusal skills [13]. 

Prevention approaches also include community policies and laws ranging from access to contraceptives for those under age 18 to graduated driving laws in which new drivers have restrictions on conditions under which they may drive and raising the legal drinking age to 21. Two examples relate to health policy for mature minors and the use of taxation. 

Policies that ensure minors’ right to obtain contraception without parental notification or consent and provide contraception at no cost to minors have been associated with an 8.5 percent decreased adolescent birth rate. Youth who were provided with contraception combined with sexuality education in school-based clinics were more likely to delay initiation of sexual intercourse and have lower pregnancy rates compared to youth not exposed to the intervention [14]. 

Systematic reviews of multiple studies have shown that price and tax increases on alcoholic beverages have been associated with reduction in alcohol use by adolescents and young adults, including excessive drinking and alcohol-related health problems [15]. 

Community monitoring systems are an essential element of effective prevention programmes. These assess behaviour problems, as well as risk and protective factors and can help communities apply prevention strategies relevant for that setting [16]. Several local surveys exist that have been tested in multiple countries, including the Communities That Care (CTC) Youth Survey which measures risk, protection and substance use, delinquency, violence and depression and the also, several avenues have proven effective to address child and adolescent obesity, from primary to tertiary care. These include the involvement of the family, the schools and the community in the care of overweight and obese adolescents, but also the development of strategies and policies which aim at improving the nutritional supply and environment of young people. Indeed, adolescence is a timely period to shape healthy eating and exercise habits that can contribute to physical and psychological benefits during the adolescent period and to reducing the likelihood of nutrition-related chronic diseases in adulthood. 

Finally, the prevention of injuries is mainly improved through environmental and legislative measures such as enforced control of firearms, mandatory use of helmets or seat belts, or improvement of roads. 

Despite the growing evidence that prevention can be effective, most preventive interventions have been developed in high-income countries. Even in high-income countries like the United States, prevention approaches that are not effective or have not been evaluated are more widely used than prevention programmes that have been tested and found to be effective. The underutilization of effective programmes in LMICs is even greater, where fewer prevention programmes have been tested. One current challenge is how the use of tested, efficacious prevention policies and programmes can be extended globally while recognizing that communities and nations are different from one another and need to decide locally what policies and programmes they use, because risk and protection factors as well as the cultural and the political context vary by community. 

First, the marketplace (government, public health agencies, schools and parents) must recognize that adolescent health is a priority, behaviour problems are implicated in poor health outcomes in adolescence and adulthood and there are effective policies and programmes that can prevent behaviour problems. A shift of 10 percent of the total funds spent on adolescent health and education to effective prevention policies and programmes could make a big difference in adolescent and adult morbidity and mortality worldwide. 

Second, more research is needed on the impact of translating these efficacious approaches to a range of communities and across nations. Translation of effective approaches must recognize differences in local conditions, but also recognize that the policy or programme has active ingredients that need to be preserved in order for the programme to work. Some interventions created in high-income countries can be translated to and be effective in LMICs. Third, using surveys to understand country and community epidemiology can help assess and address local needs with efficacious prevention programmes. By regularly assessing local risk and protective factors and behaviour problems in youth, communities and nations can understand and prioritize their need for specific prevention approaches. 

There are no simple answers to these considerable challenges. Rather, responses will need to be made at multiple levels and in the different settings in which young people are growing up. They include the provision of youth-friendly healthcare, the development, implementation and evaluation of strategies at school and community levels for promoting the health development of the young, the implementation of legislative and environmental policies that take into account local culture and history and the engagement of public health professionals with fields well beyond health in the implementation of these strategies.

1. Innocenti Research Centre. An Overview of Child Well-Being in Rich Countries. Geneva: UNICEF, 2007.

2. Beaglehole, R., et al. "Priority Actions for the Non-Communicable Disease Crisis." The Lancet, vol. 377, 2011, pp. 1438-47.

3. Gore, F.M., et al. "Global Burden of Disease in Young People Aged 10-24 Years: A Systematic Analysis." The Lancet, vol. 377, 2011, pp. 2093-102.

4. Capua, T., et al. "Update on Adolescent Immunizations: Selected Review of US Recommendations and Literature." Current Opinion in Pediatrics, vol. 25, 2013, pp. 397-406.

5. Bhutta, Z., et al. Systematic Review of Preconception Health Risk and Interventions. Geneva: WHO, 2011.

6. Patton, G.C., et al. "Global Patterns of Mortality in Young People: A Systematic Analysis of Population Health Data." The Lancet, vol. 374, 2009, pp. 881-92.

7. Coie, J.D., et al. "The Science of Prevention: A Conceptual Framework and Some Directions for a National Research Program." American Psychologist, vol. 48, 1993, pp. 1013-22.

8. Catalano, R.F., et al. "Prevention of Substance Use and Substance Use Disorders: The Role of Risk and Protective Factors." In Y. Kaminer and K.C. Winters (Eds.), Clinical Manual of Adolescent Substance Abuse Treatment, American Psychiatric Publishing, 2011, pp. 25-63.

9. Bond, L., et al. "The Gatehouse Project: Can a Multilevel School Intervention Affect Emotional Well-Being and Health Risk Behaviours?" Journal of Epidemiology and Community Health, vol. 58, 2004, pp. 997-1003.

10. Olds, D.L., et al. "Long-Term Effects of Nurse Home Visitation on Children’s Criminal and Antisocial Behavior: 15-Year Follow-Up of a Randomized Controlled Trial." Journal of the American Medical Association, vol. 280, 1998, pp. 1238-44.

11. Spoth, R.L., et al. "Randomized Trial of Brief Family Interventions for General Populations: Adolescent Substance Use Outcomes 4 Years Following Baseline." Journal of Consulting and Clinical Psychology, vol. 69, 2001, pp. 627-42.

12. Duflo, E., et al. "Education and HIV/AIDS Prevention: Evidence from a Randomized Evaluation in Western Kenya." World Bank Policy Research Working Paper 4024, World Bank, 2006.

13. Faggiano, F., et al. "The Effectiveness of a School-Based Substance Abuse Prevention Program: 18-Month Follow-Up of the EU-Dap Cluster Randomized Controlled Trial." Drug and Alcohol Dependence, vol. 108, 2010, pp. 56-64.

14. Zabin, L.S., et al. "Evaluation of a Pregnancy Prevention Program for Urban Teenagers." Family Planning Perspectives, vol. 18, 1986, pp. 119-26.

15. Wagenaar, A.C., and Toomey, T.L. "Effects of Minimum Drinking Age Laws: Review and Analyses of the Literature from 1960 to 2000." Journal of Studies on Alcohol Supplement, vol. 14, 2002, pp. 206-25.

16. Mrazek, P.J., et al. Community-Monitoring Systems: Tracking and Improving the Well-Being of America’s Children and Adolescents. Society for Prevention Research, Falls Church, VA, 2004. http://www.preventionresearch.org/CMSbook.pdf.