Adolescent health epidemiology
- Mortality rates are low in adolescents compared with other age groups and have shown a slight decline in the past decade.
- Globally, the leading causes of death among adolescents are road injury, HIV, suicide, lower respiratory infections and interpersonal violence.
- HIV-related deaths have more than tripled since 2000, making it the number 2 cause of death among adolescents worldwide.
- Depression, road injuries, iron deficiency anaemia, HIV and suicide are the major causes of disability-adjusted life years lost in 10–19 year olds.
- The African Region has the highest rates of disability-adjusted life years among adolescents.
- Nearly 35% of the global burden of disease has roots in adolescence.
Leading causes of death
In 2012 an estimated 1.3 million adolescents died, down from 1.5 million in 2000. The mortality rate decreased from 126 to 111 per 100 000 between 2000 and 2012. This modest decline of about 12% continues the trend of the past 50 years. Mortality rates dropped in all regions and for all age groups except 15–19 year old males in the Eastern Mediterranean and the Americas regions.
The leading causes of death among adolescents in 2012 were:
- road injury
- lower respiratory infections, and
- interpersonal violence.
There are two important differences from the 2000 mortality data. HIV-related deaths have more than tripled since 2000, making it the number 2 cause of mortality among adolescents. In contrast, in 2000 HIV was not even among the top 10 causes of death.
Morbidity is also important for defining public health priorities for adolescence. Morbidity data allow assessment of the many non-fatal diseases and conditions that develop during adolescence, which not only have implications for service provision today but often also have life-long repercussions.
Years lost to disability (YLD) are estimates based on prevalence data, real or imputed, that quantify the burden of morbidity and facilitate comparisons of various diseases and conditions. As with other estimates, they need to be interpreted with caution since they depend on both the accuracy of reporting, which often is not good, and the methods and assumptions built into the modelling.
There were few significant changes in the top 5 YLDs between 2000 and 2012, and the commonalities across regions and between high income countries and low and middle income countries remain.
The top five ranked causes of YLDs in 10-14 year olds are:
- unipolar depressive disorders
- iron deficiency anaemia
- back and neck pain, and
- anxiety disorders.
They are similar for 15-19 year olds except asthma is replaced by alcohol use disorders, the number 2 cause of YLDs in 15-19 year old males. These conditions are responsible for nearly 50% of YLDs in adolescents 10-19 years.
Disability-adjusted life years: Combining mortality and morbidity
What are DALYs?
Disability-adjusted life years (DALYs) are a measure of the years of healthy life lost due to ill health, disability or premature death. They estimate the gap between current health status and an ideal health status, with the entire population living to an advanced age free of disease and disability.
For a specific health condition, DALYs are calculated as the sum of the years of life lost (YLL) due to premature death plus disability (YLD) for people living with the health condition.
Between 2000 and 2012 overall DALYs for adolescents decreased from 165 to 152 per 1000 population, or 8%, less than half of the 17% decline overall for all age groups.
The African Region continues to account for the highest DALYs (in 2012, 300 DALYs per 1000 population). The lowest DALYs are in the high income countries and the Western Pacific Region (both 84 per 1000 population, in 2012). The Eastern Mediterranean, South-East Asian, Americas and European regions lie between these extremes (at 165, 148, 125 and 111 per 1000 population in 2012, respectively).
DALYs declined between 2000 and 2012 for all adolescents except for 15–19 year old males in the Eastern Mediterranean Region and Americas Region. DALYs for all adolescents declined most in the South-East Asia Region (21%) and the Western Pacific and European regions (16% and 17% respectively). The smallest declines took place in the Eastern Mediterranean Region (4%).
The major causes of DALYs changed little between 2000 and 2012. In 2012, depression, road injuries, iron-deficiency anaemia, HIV and intentional self-harm were the top five global causes of DALYs for adolescents. The one notable change from 2000 was that HIV ranked number 4 among causes of DALYs in 2012. In 2000 it was not among the top 10.
So, what do we know?
All the measures of death, disease and disability tell a similar story about adolescent health. Generally, there is remarkable consistency across ages, sexes and regions and between low and middle income countries and high income countries.
While there are many similarities between 2000 and 2012, trend data reveal both successes (measles down) and challenges (HIV and war-related deaths and DALYs up).
Several points stand out:
- Many of the health problems seen in adolescence start during the first decade, emphasizing the need for programming across the life-course.
- The mortality and morbidity/disability patterns of adolescence reflect the transition from childhood to adulthood and the impact of the developmental processes taking place during this period.
- Important gender differences include more interpersonal violence and war-related deaths among male adolescents and maternal problems affecting females, although the latter have decreased significantly between 2000 and 2012.
- There are more similarities than differences among regions and between high and low/middle income countries.
- The increase in global HIV-related deaths results primarily from high mortality among adolescents in the African Region.
- The statistics expose some largely neglected issues in adolescent health: mental health problems, suicide, alcohol use, road injuries and other unintentional injuries, interpersonal violence and war.
- Common infectious diseases continue to be a major problem.
The estimates of mortality, morbidity and DALYs provide a strong argument to shift thinking away from the assumption that adolescence is generally a healthy period and so needs little attention. Yes, most adolescents are healthy most of the time. But many adolescents have health problems that require serious attention from the health sector, particularly since many conditions and behaviours that start or are reinforced during adolescence affect health across the life-course.