Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by inattention, hyperactivity and impulsivity. ADHD begins in childhood and often persists into adulthood. While the exact causes of ADHD are unknown, research suggests that genetics, brain changes and environmental factors play important roles.
ADHD has been found to have strong associations with a number of other conditions and factors. Understanding these links is important as it can help improve diagnosis, treatment and overall management of ADHD.
Twin studies have shown that ADHD often runs in families and that the heritability rate is around 70-80%. This means that genetics play a major role. Specific genes that have been implicated include those involved in dopaminergic and serotonergic activity. However, there are likely many genes involved, each making small contributions to ADHD risk. Environmental factors are also important and likely interact with genetic vulnerabilities.
Brain Structure and Function
Imaging studies show there are structural and functional differences in the brains of people with ADHD compared to those without ADHD. For example, children with ADHD tend to have slightly smaller brain volume in regions that control executive functioning. There are also connectivity differences between brain networks.
The neurotransmitter systems most implicated are those involving dopamine and noradrenalin. It is believed that imbalances or deficiencies in these neurotransmitters may underlie some of the symptoms of ADHD. Genes influencing these neurotransmitters may be a factor.
Traumatic Brain Injury
Children who have had a traumatic brain injury (TBI) are more likely to develop ADHD compared to peers with no brain injury. Even mild TBI can increase risk. The blow to the head may cause frontal lobe damage and disruptions in dopamine and noradrenalin activity.
In one study, nearly a quarter of children with TBI went on to develop ADHD within 2-5 years after their injury. Rates were highest if the injury occurred pre-school age.
Being born significantly pre-term (under 32 weeks) or at an extremely low birth weight is linked to a higher chance of ADHD symptoms. This is likely due to immature brain development. The more premature the birth, the greater the risk.
One study found 25% of extremely pre-term infants went on to develop ADHD later in childhood. Difficulties with inattention and hyperactivity were most common.
Smoking and Alcohol During Pregnancy
Women who smoke cigarettes or drink alcohol during pregnancy are more likely to have a child with ADHD. Nicotine and alcohol can interfere with fetal brain development.
According to a study, children whose mothers smoked 10 or more cigarettes a day while pregnant were over 2 times more likely to have ADHD compared to those with non-smoking mothers.
Exposure to certain pesticides, chemicals and toxins in utero or during childhood may increase ADHD risk to some degree. This includes lead, organophosphates used in pesticides and flame retardants used in furniture and electronics.
The developing brain is more vulnerable to damage from such neurotoxins. However, more research is needed to confirm specific environmental risk factors for ADHD.
Children from families of low socioeconomic status appear to have a heightened risk of developing ADHD symptoms. Poverty can be linked to poor prenatal care, maternal stress, malnutrition, exposure to environmental toxins, inadequate medical care and less access to support services.
One study found ADHD rates were 10% higher for children of low SES families compared to high SES families. However, it’s unclear exactly how much various social and environmental factors contribute to the increased risk.
Sleep difficulties are common in children and adolescents with ADHD and seem to be bi-directional – ADHD disrupts sleep, and inadequate sleep exacerbates ADHD symptoms. Having a sleep disorder like sleep apnea may also raise risk.
Poor or inadequate sleep negatively impacts mood, focusing ability, hyperactivity and cognitive functioning. Establishing healthy sleep patterns is an important part of managing ADHD.
Up to 30% of children with ADHD also have an anxiety disorder, such as generalized anxiety, social phobia or separation anxiety. It’s not fully clear why anxiety rates are elevated in ADHD. Contributing factors may include overthinking, hyperfocusing on threats, impulsiveness and low frustration tolerance.
Comorbid anxiety tends to make ADHD worse and harder to treat. Symptoms like restlessness, irritability, emotional volatility and trouble concentrating can all be amplified.
Between 10-20% of children with ADHD develop clinical depression. The challenges of ADHD – like relationship problems, academic underachievement and low self-esteem – can increase the risk for depression. There may also be overlapping genetic and environmental causes.
Depression combined with ADHD is linked to greater distress, social difficulty and substance abuse. Identifying and addressing depressive symptoms is an important part of ADHD treatment.
Oppositional Defiant Disorder
Oppositional defiant disorder (ODD) occurs in around 35% of children with ADHD. ODD involves frequent stubborn, hostile, defiant and disruptive behavior towards parents, teachers and other authority figures.
Children with both ADHD and ODD tend to have more severe symptoms, worse impairment, greater family conflict and more difficulties in school. Treatment focuses on teaching emotional regulation and problem-solving skills.
Adolescents and adults with ADHD have a significantly elevated risk of substance abuse issues involving alcohol, marijuana, cocaine and other stimulant drugs. These substances may be used as a form of self-medication for ADHD symptoms.
Impulsiveness, poor decision making skills and difficulty controlling urges can also contribute to substance abuse problems. Addressing ADHD is an important part of addiction recovery in these individuals.
Several studies have found links between ADHD and obesity, with rates of obesity increased two-fold in children with ADHD. Impulsivity around food, a lack of planning and dopamine dysregulation may play a role.
Additionally, some of the medications used to treat ADHD can increase appetite and weight gain. A healthy diet and regular exercise should be encouraged for all children with ADHD.
Coordination and Motor Control Problems
Up to 50% of children with ADHD experience some degree of developmental coordination disorder (DCD). This involves difficulties with balance, handwriting, scooting, running and other motor skills.
Some overlapping brain regions and dopamine pathways are involved in both ADHD and motor control. DCD combined with ADHD tends to cause greater impairment in school activities and sports.
Sensory Processing Issues
Around 30-50% of people with ADHD have sensory processing problems. They may be oversensitive or undersensitive to stimuli like noise, touch, sights and movement. As a result they may seek intense sensory experiences or actively avoid certain sensations.
Sensory issues in ADHD can lead to distractibility, anxiety, aggression and avoidance behaviors that exacerbate symptoms. Behavioral therapy and sensory integration education can help manage sensory problems.
ADHD occurs in around 30% of children with seizure disorders like epilepsy, while only 5% of the general population has ADHD. ADHD is linked specifically to absence seizures and petit mal seizures that most commonly arise in childhood.
Seizures and ADHD appear to share some underlying neurological features. Similar neurotransmitter systems are implicated in both conditions.
Around 30% of children with autism also meet criteria for ADHD. Both conditions involve problems with communication, social interaction, repetitive behaviors and executive functioning skills.
Autism and ADHD may have some overlapping genetic and environmental risk factors. Identifying both conditions leads to more targeted and effective interventions.
Tics or Tourette Syndrome
Tics, Tourette Syndrome and ADHD co-occur in 20-60% of cases. It is thought they arise from similar dysfunction in motor control pathways in the brain that utilize dopamine and serotonin.
The combination of tics/Tourette’s with ADHD is linked to greater cognitive issues, anxiety and obsessive-compulsive symptoms. Careful medication management is required to avoid worsening tics.
Learning Disabilities and Disorders
Up to 45% of children with ADHD also have a learning disability (LD) such as dyslexia, dysgraphia or dyscalculia. Cognitive weaknesses in areas like reading, writing and math make academic tasks more challenging.
ADHD combined with LDs lead to poorer educational outcomes. Addressing both conditions improves school performance and promotes success.
Around 5-10% of children identified as gifted also have ADHD. The mix of high intellectual ability and ADHD traits can be paradoxical. While giftedness is an asset, untreated ADHD symptoms like inattention and disorganization may hinder a child from achieving full potential.
Identifying and managing ADHD allows the strengths of gifted children to flourish. Special accommodations may help gifted ADHD students thrive academically.
Speech and Language Disorders
Various speech and language problems occur more frequently in children with ADHD, including:
- Speech sound errors
- Impaired grammar/syntax
- Poor vocabulary knowledge
- Difficulty understanding directions
Between 30-50% of children with ADHD experience some kind of speech-language impairment. It can contribute to problems with reading, writing, following instructions and socializing.
Delayed Development of Executive Functions
Many children with ADHD lag behind their peers in developing key executive functions like:
- Impulse control
- Working memory
- Planning and prioritizing
These deficits lead to many real-world difficulties in areas like completing assignments, controlling behavior, staying focused and managing time. Maturing executive function skills is a treatment target.
ADHD is associated with emotional control problems in about 25% of cases. Issues include:
- Low frustration tolerance
- Frequent mood swings
- Trouble managing anger
- Overreacting to small problems
- Taking criticism poorly
Impulsiveness, poor self-soothing skills and difficultly expressing emotions contribute to emotional dysregulation. Counseling and parenting programs can teach coping strategies.
Greater Risk of Injuries
Children with ADHD are more prone to injuries than their peers. Issues with impulsivity, inattention and hyperactivity all contribute to increased risk-taking and accidents.
One study found children with ADHD were 50% more likely to suffer a non-fatal injury requiring medical treatment compared to children without ADHD.
Common injuries include:
- Cuts and bruises
- Broken bones
- Head injuries
Ongoing supervision, training in safety practices and avoiding dangerous situations can help reduce injury risk.
Higher Rates of Emergency Room Visits
Children with ADHD are brought to emergency rooms for care 30-40% more often than those without ADHD. The types of common injuries listed above frequently necessitate ER visits.
Higher rates of hospitalization from accidents and greater need for emergency medical services also drain family financial resources and increase costs for healthcare systems.
More Doctor’s Visits and Use of Medical Services
Managing ADHD requires frequent doctor’s appointments for assessment, treatment follow-up and refilling prescriptions. Children with ADHD also tend to have more illnesses and health complaints that require medical care.
Families of children with ADHD spend around $2,500 more on healthcare expenses per year compared to other families. Ongoing care coordination improves outcomes.
Higher Rates of Traffic Accidents and Violations
Teenagers and adults with untreated ADHD are involved in significantly more motor vehicle crashes compared to the general public. Estimates range from being 1.5 to 4 times more likely to be in an accident.
Factors like inattention, distractibility, impatience and reckless driving increase accident risk. ADHD drivers also accumulate more speeding tickets, are cited more often for reckless driving and have licenses suspended or revoked more frequently.
ADHD-related driving difficulties include:
- Difficulty maintaining lane position
- Failure to observe traffic signals or signs
- Poor braking reaction time
- Making quick turns or lane changes without signaling
- Zoning out during driving
ADHD screening and management helps create safer teen and adult drivers.
Increased Risky Sexual Behaviors
ADHD is linked to earlier sexual activity, more sexual partners, less contraception use and higher rates of sexually transmitted infections in teens and adults.
Impulsiveness and poor decision-making contribute to risky sexual behaviors. Comprehensive sex education and coaching in relationship skills should be part of ADHD treatment.
In summary, ADHD has been strongly associated with a number of medical, developmental, psychiatric, cognitive and behavioral conditions. Understanding these connections allows for better screening, diagnosis and treatment approaches.
A holistic perspective that addresses ADHD along with any co-existing disorders or impairments leads to better long-term outcomes. With appropriate treatment and support, individuals with ADHD can thrive academically, socially and emotionally.