In addition to diagnostic (e.g., asthma, diabetes) and functional definitions (e.g., intellectual disability), common features of the many different definitions of a chronic health condition include the following:

As opposed to permanency, most chronic conditions are defined by a prolonged or episodic course and an impact that can change with growth and development. For example, cerebral palsy is the result of a static developmental insult, yet the requirement for orthopedic surgery in adolescence results from dynamic growth. Physical health conditions, behavioral and emotional disorders including neurodevelopmental conditions (e.g., attention deficit hyperactivity disorder [ADHD]), and related disorders (e.g., substance abuse) are all considered chronic health conditions, based on the presence of associated impairments or disability. In this regard, disability is viewed as an overarching term for impairments at the level of the body, the person, and the person in social situations, which result in limitation of activities or restrictions to full participation in age-appropriate activities.¹

In contrast to a definition based on the presence of impairments or disabilities, the term “Children with Special Health Care Needs” refers to children with one or more chronic physical, emotional, developmental, and behavioral conditions who also require health and related services of a type or amount beyond that required by children generally.² This definition is equally inclusive of a wide variety of conditions, and is as relevant for AYAs as it is for children.

Over the past few decades, technical advances have resulted in dramatic improvements in the survival of children with conditions that were largely considered fatal in childhood, such as congenital heart disease, cystic fibrosis, and spina bifida. The majority of adolescents with such conditions now expect to survive into adulthood.³

Disease-specific surveys are able to describe the incidence and prevalence of conditions, and how this has changed over time. There is a real increase in the incidence of certain conditions, such as type 1 diabetes, allergies and anaphylaxis, and chronic inflammatory bowel disease. Other surveys demonstrate increasing prevalence in certain conditions over time, such as overweight and obesity with a resultant increase in hypercholesterolemia, hypertension, metabolic syndrome, and type 2 diabetes, especially in young adults. In many parts of the world, treatment of human immunodeficiency virus (HIV) infection has resulted in HIV/acquired immunodeficiency syndrome now being largely considered to be a chronic health condition.

The extent of emotional disorders in AYAs is increasingly appreciated, as is the effect of puberty on risk of onset.⁴ One in four young people have experienced a mental health disorder over the past year.⁵ The most common conditions are mood and anxiety disorders (e.g., depression), behavioural and neurodevelopmental disorders (e.g., ADHD, conduct disorder) and substance use disorders. Comorbidity between different mental health disorders is apparent in adolescence and young adulthood, as is the co-occurrence of chronic physical conditions with mental health conditions.⁵

However, even for the same condition, the use of different definitions of a condition within different surveys nationally and internationally can yield inconsistent estimates. The difficulty in obtaining a picture of the incidence and prevalence of chronic
health conditions in adolescence and young adulthood is further compounded by poor assessment across adolescence and young adulthood. Many surveys span childhood and adolescence; however, data for adolescents are inconsistent due to the use of different age-cuts (e.g., 10 to 14 years, 15 to 19 years versus 11 to 13 years, 14 to 15 years, 16 to 17 years). Other surveys do not report adolescent data separately (e.g., 0 to 17 years). The prevalence of different chronic health conditions in young adulthood is not well appreciated as many age-cuts fail to bring visibility to this age group (e.g., 14 to 65 years, 18 to 40 years, 18 to 65 years).

Much advocacy around AYAs with chronic health conditions has successfully influenced policy by focusing on a specific condition or group of similar conditions (e.g., mental health conditions, cancers). In this regard, disease-specific surveys can be very valuable in measuring the changing incidence or prevalence of a particular condition, the presence and type of unmet health care needs, access (or lack of access) to health insurance, and particular educational or employment challenges. In addition to disease-specific advocacy, other policies are best advanced by understanding the issues affecting chronic health conditions in AYAs as a group. For example, the relative proportion of time that specialist medical training programs dedicate to AYA health would be better supported by surveys that describe the broad prevalence of chronic health conditions, rather than by individual conditions. Similarly, knowledge of the extent of comorbid physical and mental health conditions has the potential to alter models of health care delivery to AYAs. In this regard, the 2009 to 2010 National Survey of Children with Special Health Care Needs in the United States found that 18.4% of 12- to 17-year-olds had special health care needs in comparison to 9.3% of 0- to 5-year-old children.⁶ That is, the prevalence of special health care needs increases with age across adolescence, and increases further again into young adulthood. Of these children, 66% had health conditions that consistently or moderately affected their daily activities, while 16% had missed 11 or more days of school in the past year. Such information can also help support more generic interventions, such as the concept of a “medical home” that is built on the notion of quality health care, continuity of care, and patient- and family-centered care together with expectations of comprehensive and accessible services.⁷

The two defining aspects of biological development in adolescence, namely puberty and neurocognitive maturation, can have even more profound implications for adolescents with chronic health conditions than their healthy peers. The interaction of chronic health conditions with adolescent development is complex and bidirectional; the health condition may affect development and/or development may affect the condition. For example, some chronic health conditions, such as chronic renal failure and anorexia nervosa, can cause pubertal delay, changing the timing and trajectory of peak height velocity. When extreme, these changes can result in stunting of adult height. For other conditions such as asthma, the onset of puberty can reduce the severity of the disease, while the reverse is more typical in diabetes mellitus, with onset of puberty a risk for poor metabolic control. Regular monitoring of growth and puberty is an important component of health care for all adolescents with chronic health conditions.

During adolescence, the fundamental cognitive and problem-solving skills acquired in earlier childhood undergo further development.⁸ Cognitive maturation results in greater capacity for insights around the significance of life-limiting conditions, such as cystic fibrosis, which may contribute to anxiety and depression. A growing capacity to maintain attention, greater working memory, and inhibitory control of emotions promote the development of more goal-directed activities, which bring greater capacity for self-management of chronic health conditions. Importantly, future planning skills continue to develop well into the mid-20s, with particular implications for adherence to treatment. Social cognition, or the ability to make sense of the world through the processing of signals from others, accelerates from puberty and is central to interpersonal functioning, mental health and well-being, educational attainment, and future employment.⁹ The effects of deficits in such cognitive skills, that can occur in a range of neurodevelopmental and mental health conditions, are commonly amplified in late childhood and adolescence. Regardless of the cause (e.g., mobility limitations, parental overprotectiveness), fewer opportunities for peer engagement will reduce opportunities for social and emotional learning, social confidence, and self-esteem.

The social determinants of health influence health outcomes in AYAs with chronic health conditions.¹⁰ Structural determinants such as national economic wealth will influence the availability of health insurance, education, and employment, which are all relevant for young people with chronic health conditions and their future health and life opportunities. More proximal determinants, also known as risk and protective factors, operate within the individual and their family, peers, school, and community. A chronic health condition is a risk factor within the individual domain that, when compounded by risks within other domains (e.g., family dysfunction, bullying, unsupportive schooling, high rates of youth unemployment), can influence adolescents’ and young adults’ engagement in health-related behaviors (e.g., tobacco use) and states (e.g., depression). For example, bullying increases the likelihood of a number of health-related behaviors and states, including substance misuse, unsafe sex, depression, antisocial and illegal activities, and dangerous driving.¹¹

Given the importance of academic success for future employment, promoting school engagement by minimizing school absenteeism from illness and medical appointments is important. However, beyond academic achievement, schools are important social environments for adolescents with chronic health conditions that promote peer connections, emotional control, and well-being. Peer support groups, whether face-to-face or online, can be helpful in normalizing the differences young people with chronic health conditions can experience,¹² which may consequently promote well-being and continued engagement with schooling.

Many studies have explored the question of whether adolescents with chronic health conditions have a higher rate of mental health disorders. Most robust studies suggest that this group has an elevated risk¹³ that is largely mediated by the same factors as in healthy young people such as family connectedness.¹⁴ Youth with certain conditions, such as physical and intellectual disabilities, appear to be at even higher risk.

Many health professionals might assume that AYAs with chronic health conditions, especially when severe, would be less likely than their healthy peers to engage in health-related behaviors such as unsafe sex, or unsafe alcohol or drug use. However, there is little evidence to support this notion. Instead, studies suggest that young people with chronic health conditions are as likely, if not more likely, to engage in health-related behaviors.¹⁵ The explanation for potentially higher rates is unclear. At least some of the increased risk is mediated through depression. Part of the explanation may reflect biological differences in cognitive processing that result in a different appreciation of the risk associated with particular behaviors (e.g., ADHD). However, a more simple explanation may be the greater challenge to feel “normal” experienced by many AYAs with chronic health conditions, which may render them more sensitive to perceived peer norms in order to fit in socially.

What is apparent is that the risks of certain health-related behaviors are greater for AYAs with particular chronic health condition.³ For example, while smoking is unhealthy for all young people, it is even more damaging for AYAs with diabetes, due to its effect on microvascular and macrovascular disease. It is similarly more risky for young people with chronic lung or cardiac conditions. In the same way, while heavy alcohol use is unsafe for all, alcohol can lower the seizure threshold for young people with epilepsy, and make blood glucose control more challenging in those with diabetes.

Within many children’s services, most support services and physical facilities remain oriented to young children as they constitute the age group that has historically been the major user of such facilities. Yet, around the world, as the upper age of specialist pediatrics increases and the proportion of adolescents managed by pediatricians and specialist children’s services grows, services and facilities need to become better aligned to adolescents with chronic health conditions, because young people require different approaches from their health care providers and health services than those oriented to younger children.¹⁶