Epidemiology and overview of the burden of disease in adolescents

HELEN WEISS: In this step, we’re going to talk about the demographic and epidemiological transitions, and they are important for adolescent health. Adolescence represent 1/6 of the world’s population. In 2015, there were just over 1.2 billion adolescents in the world, the most they have ever been. And that’s estimated to increase gradually to about 1.3 billion by 2050. Out of the total population, the proportion who are adolescents vary substantially by region, with the greatest proportion in the least developed countries, and the smallest proportions in the industrialised countries. More than half of all adolescents globally live in Asia. In absolute numbers, South Asia is home to more adolescents– around 340 million– than any other region.

It is followed by East Asia and the Pacific, with about 277 million. The adolescent population of either of these regions dwarfs that of any other region in the world. Sub-Saharan Africa is the region where adolescents make up the greatest proportion of the population, with 23% of the region’s population age 10 to 19.

The trends in population in different regions of the world differ substantially. As one can see here, it is projected that there will be a substantial decline in the number of adolescents in the East Asia and Pacific region over the next 35 years. In contrast, the numbers in sub-Saharan Africa, where adolescents already make up 23% of the total population, will continue to increase substantially through to 2050 and beyond. We are witnessing a demographic transition. Rapidly falling fertility rates and huge increases in the number of children surviving to adolescence have created the largest cohort of adolescents that we have ever seen. In parallel to this demographic transition, there is an epidemiological transition.

This is being caused by declines in infectious diseases in childhood, such as diarrheal diseases and pneumonia, and the increasing importance of non-communicable conditions, which have implications on the health needs and programming priorities for adolescents. A growing urgency now are the increasing non-communicable conditions, such as injuries, mental health disorders, diabetes, and cardiovascular diseases in early life. So why are these transitions so important? It is because countries have a one-time only opportunity to invest in a large proportion of the population who are young adults in their most productive years. But to realise this potential dividend, individuals must leave adolescence and into adulthood healthy, well-educated, and employed.

To ensure that these healthy transitions happen, we have to understand what the health priorities in adolescence are. In 2015 alone, an estimated 1.2 million adolescents age 10 to 19 years died. Nearly all of these deaths are preventable. Currently, the top five causes of death globally among adolescents are road injury, lower respiratory tract infections, suicide, diarrheal diseases, and drowning. Other major causes of adolescent deaths include interpersonal violence and HIV/AIDS. To address these deaths, we have to remember that social determinants of health, such as the norms of the culture you’re living in, the environment that you’re living in, the particular risk and protective factors– such as whether you have parental care and concern– are important.

They can also include factors such as education and employment, marriage and parenthood, marketing and digital media, and the quality of universal health coverage. The health-related behaviours in states, such as smoking, alcohol consumption, and drug use, all can lead to specific adolescent health outcomes, which continue to have an impact throughout adult life.

We can see here that there are regional variations, with most deaths and low middle income countries, and highest mortality in Africa, which accounts for 45% of adolescent deaths in the low middle income countries, followed by Southeast Asia, which accounts for 26%.

Mortality is relatively low in the adolescent age group compared with other age groups, but the burden of disease is high, due to lifelong morbidity resulting from conditions with onset in adolescence. So what is burden of disease? This is a combination of mortality and morbidity. Mortality contributes the years of life that you’ve lost if you die from a condition. Morbidity contributes the years of life lived with disability, which take away from those years. For example, if you were bedridden for an acute illness for one year, and then you recover completely, that would contribute almost an entire disability-adjusted life year. This combined measure is a disability-adjusted life years lost.

QALYs are another measure of disease burden, which look at both the quality and the quantity of life lived. QALYs are years gained in perfect health, where DALYs are the measure of years of perfect health lost due to illness. In this presentation, we will focus mainly on DALYs.

So what’s causing this burden of disease in adolescents? When we look at the top five causes of burden of disease in adolescents, as opposed to simply mortality, we see a subtle difference. Still, we can see the importance of road injuries, and then depression, and iron deficiency– anaemia. When thinking about health outcomes or risk factors for disease burden, it is important to consider differences between both sex and age groups. Among female adolescents of all ages, anxiety disorders an iron deficiency anaemia are a consistent cause of ill health.

However, in the 10 to 14-year-olds, the infectious disease is associated with younger age groups continue to cause a significant burden, with lower respiratory tract infections, diarrheal diseases, and meningitis making up the rest of the top five. In the older, 15 to 19 year group, this changes, with depressive disorders, maternal conditions, and self-harm replacing the three infectious diseases.

For males, this picture is slightly different. We can see here that anaemia is also the top cause of DALYs lost in 10 to 14-year-olds, however, road injury, interpersonal violence, self-harm, depressive disorders, and drowning are the top causes. These changes in disease patterns mean that the risk factors for disease shift from unsafe water, unsafe sanitation, and inadequate handwashing to alcohol and drug use, unsafe sex, and intimate partner violence.

One of the key things to note is that the burden of non-communicable health conditions has been increasing dramatically globally for all age groups. These are due to injuries, mental health disorders, cardiovascular disease, and diabetes, as well as obesity. Most of these either have their biggest effects during adolescence, such as injuries. They present for the first time during adolescence, such as many mental health disorders, or the behaviours and risk factors that start during adolescence lead to cardiovascular disease or diabetes and obesity in later life.

All of this is intensified in humanitarian and fragile settings, including some burdens related to malnutrition, disability, unintentional injury, violence, sexual and reproductive health needs, water sanitation and related health needs– e.g., menstrual hygiene management– and mental health. Adolescence is a period when many risky or protective behaviours start or are consolidated, having a major impact on health as adults. Examples include diet and physical activity, substance use, and sexual risk behaviours. To appreciate this, we must take a life course perspective, and think beyond immediate causes of mortality and morbidity to include risk and protective factors.

And all of these factors are affected by the local environment, and also the social, educational, and economic policies environment that you’re in, and the particular health policies that you’re living with in the country that you’re living in. So what are the most important risk factors? Alcohol or tobacco use, lack of physical activity, unprotected sex, and/or exposure to violence can all jeopardise not only of your current health, but also health of adults, and even the health of future children. Promoting healthy behaviours during adolescence and taking steps to better protect young people from health risks are critical for the prevention of health problems in adulthood, and the country’s future health and ability to develop and thrive.

But we must be mindful that adolescents’ needs differ across contexts age and effects. Some adolescents are particularly vulnerable, experiencing higher exposure to health risks, lower access to health services, worse health outcomes, and greater adverse social consequences as a result of ill health. Particularly vulnerable adolescents include those living with disabilities or chronic illnesses, stigmatised and marginalised because of sexual orientation, gender identity, or ethnicity, or living in humanitarian and fragile settings, where they often experience multiple and compounded vulnerabilities. Investing in adolescents now will have a huge impact on future generations.