What Is ADHD? Everything You Need to Know About Attention Deficit Hyperactivity Disorder
Causes and Risk Factors for ADHD
Experts aren't sure what causes ADHD. Research suggests that the disorder has a strong neurobiological basis and that heredity is a major factor. (11)
Neuroimaging studies using MRIs to look at brain structure have found a consistent set of neural circuits to be associated with ADHD. These circuits are related to sustained attention, control of inhibitions, motivation, and regulation of emotions. (12)
But it’s unclear whether ADHD behaviors result from abnormal neural connections or whether there is neural adaptation because of symptoms.
Imaging studies have shown that certain areas of the brain are smaller in children with ADHD compared with children who don’t have ADHD. Two meta-analyses found that these differences in brain volume are no longer detectable in adulthood, suggesting that ADHD symptoms may be due, in part, to delays in development or maturation. (12)
Several factors may increase a child's likelihood of developing ADHD:
Geneticsappear to play the largest role. ADHD has been shown to run in families, and studies have estimated that heritability may range from 60 to 90 percent. (12)
Although the specific genes at play have not yet been identified, scientists believe multiple genes may be involved, because it’s such a complex condition. (13) These genes may have to do with the processes of certain neurotransmitters, such as dopamine, which plays a role in the brain’s reward systems and in regulating impulsivity and movement.
Environmental exposure to toxins and chemicals, especially tolead, may be a contributing factor. Studies have indicated a relationship between ADHD and levels of lead in the bloodstream. One 2010 study, published in theJournal of Child Psychology and Psychiatry, found that lead exposure was associated with the impulsivity-hyperactivity combined type of ADHD, but not the inattentive type. (14)
Alcohol or tobacco use during pregnancyhas been associated with ADHD symptoms in children in a number of studies. But more recent research has questioned whether the use of these substances directly causes ADHD.
A study published in April 2019 in theJournal of Child Psychology and Psychiatryfound no support for a causal association between smoking during pregnancy and ADHD. (15) Similarly, a study published in October 2019 in theInternational Journal of Epidemiologyfound that maternal alcohol use during pregnancy was weakly, though perhaps causally, associated with reported ADHD symptoms but not with clinical diagnoses of ADHD. (16)
Still, pregnant women should refrain from alcohol consumption and smoking because of other well-established risks.
Traumatic brain injury (TBI)in early childhood has been linked to the development of psychiatric disorders. Among those disorders, ADHD is the most common, with a prevalence of about 20 percent, notes a study published in March 2019 inJAMA Pediatrics.(17)
TBI is not uncommon — more than 1 million children and young adults seek emergency treatment for it each year.
Premature birth or low birth weightmay increase the risk for ADHD. Some research has suggested a correlation along a gradient — that the lower the birth weight or the higher the preterm level, the greater the risk of ADHD. A meta-analysis and review of 34 studies, published in January 2019 inPediatricsconfirmed this, showing an even stronger association with the development of ADHD when birth weight was extremely low or the birth was extremely preterm (which the World Health Organization defines as before 28 weeks. (18)
Diet and behavioral factorssuch as consuming too much sugar or food additives or excessive screen time (television, smartphones, tablets, and computers) have been associated with ADHD. While these factors may affect or exacerbate symptoms, research doesn't support claims that they cause ADHD.
Video: Does my Child Have ADHD?
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