A Practitioner Review from The Journal Of Child Psychology and Psychiatry summarizes what causes Attention Deficit Hyperactivity Disorder, ADHD, as follows:
No single risk factor explains ADHD. Both inherited and noninherited factors contribute and their effects are interdependent1.
So no one knows the exact cause of ADHD, but several risks factors and substantial components have been identified.
Hereditary Factors (Gene)
Genetic has been identified to be a substantial component2.
ADHD usually runs in the family. Family, twin, adoption, segregation analysis, and molecular genetic studies show that the heritability rates are high, around 71-90%. Children with ADHD first degree relatives (e.g. parents, siblings) are up to eight times more likely to also have ADHD.
Despite the strong inherited contribution to ADHD, environmental interactions also play a significant role because they can influence how genes are expressed throughout brain development.
The Prefrontal Cortex
ADHD is a heterogeneous disorder characterized by symptoms of inattention, impulsivity and locomotor hyperactivity.
Inside the brain, the prefrontal cortex (PFC) regulates attention, behavior and emotion. This is why injuries or lesions in PFC can also result in ADHD symptoms.
Researchers have found that the PFCs in people with ADHD are slightly different. They could be different in size, signaling, connectivity, maturity or activities. This could be why ADHD manifests different for everyone and no one treatment is for all3.
Several environmental factors have been identified to be associated with ADHD. Notice the word association. It means the associated factors are more likely to be found in people with ADHD. But since no causal relationships have been established, they may or may not be what causes the disorder.
Pregnancy and Birth
During pregnancy, exposure to tobacco smoke in utero is suspected to be associated with ADHD and ADHD symptoms in children. Besides maternal smoking, stress and (to a lesser extent) alcohol consumption have also been found associated with ADHD occurrence4.
Infants with low birth weight and prematurity are also associated, especially with the inattentive sub-type of ADHD.
But again, these are only associated risk factors. To date, no conclusive studies have been found to prove that these factors are the direct causes.
Pesticides and toxic industrial products such as PCB are both identified risk factors.
Previous studies had linked ADHD with very high levels of childhood exposure to pesticides, such as levels experienced by kids living in farming communities. But a recent study found that even children who were only exposed to the chemicals through eating pesticide-treated fruits and vegetables, had a higher risk of developing the disorder5.
Despite the lack of direct causal proofs between these factors and the disorder, they are still dangerous and proven to cause other problems, such as memory impairments. So these toxins should be avoided whenever possible.
Studies have found that ADHD symptoms are related to blood lead level6.
Lead is a toxin that should be avoided at all costs. Besides its association with ADHD occurrence, lead can cause other severe neurodevelopment damages.
Researchers have found that children from disadvantaged socioeconomic backgrounds are at a greater risk of mental health problems, including ADHD.
Financial difficulties at childhood is the strongest predictor of ADHD. Kids with younger or single mothers are also more likely to have ADHD diagnosis at age 77.
However, similar to other environmental risk factors, no conclusive causal relationships have been found8.
Early Deprivation and Neglect
While the influence of parenting on ADHD remains unclear, severe early neglect is an identified risk factor9.
Children who have been institutionalized early in life, such as orphans in Romania, are 7 times as likely to have ADHD by age 4-5 compared to children who have never been institutionalized10.
Television Viewing And Video Games
Some parents believe that watching too much TV or playing video games can result in ADHD. But after several studies found such associations, several other studies came out and refuted those claims.
The latter researchers did similar experiments or redid previous analysis using the same data. They could not come up with the same conclusion that too much TV time causes ADHD.
Further studies are needed to settle this debate. For now, although the results are inconclusive, limiting television viewing in early childhood is still a sensible parenting decision.
Nutrition and Nutritional Deficiencies
The links between ADHD and some nutritional deficiencies (e.g. zinc, magnesium and plyunsaturated fatty acides) are found in some studies but not in others. There is not enough consistent evidence to support the associations11.
Despite the lack of evidence to support the associations between nutritional deficiencies and ADHD, supplementing the diet with Omega-3 fatty acids has been found to alleviate ADHD symptoms in children12.
Food Color Sensitivities
One study found a mild correlation between food color additives and ADHD. However, when the study was re-analyzed with only FDA approved food colors, the correlation disappeared13.
Myth: Does Sugar Make Kids Hyper
Sugar have been blamed by some parents for causing ADHD. Some studies have found that high levels of sugar consumption are associated with increased rates of inappropriate behavior in some children14. However, multiple studies and meta-analysis have shown that sugar does not cause ADHD15,16.
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