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What Causes ADHD in Children – Risk Factors

Happy family of a woman, man, boy and girl, and girl runs in front, wondering what causes ADHD

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 interdependent​1​.

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 component​2​.

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

a colored illustration of a brain, shades of blue on the left brain and rainbow color on the right brain, can it be an ADHD brain

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 all​3​.

Environmental Risks

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 occurrence​4​.

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.

Industrial Toxins

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 disorder​5​.

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.

Lead

Studies have found that ADHD symptoms are related to blood lead level​6​.

Lead is a toxin that should be avoided at all costs. Besides its association with ADHD occurrence, lead can cause other severe neurodevelopment damages.

Psychosocial Adversity

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 7​7​.

However, similar to other environmental risk factors, no conclusive causal relationships have been found​8​.

Early Deprivation and Neglect

While the influence of parenting on ADHD remains unclear, severe early neglect is an identified risk factor​9​.

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 institutionalized​10​.

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 associations​11​.

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 children​12​.

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 disappeared​13​.

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 children​14​. However, multiple studies and meta-analysis have shown that sugar does not cause ADHD​15,16​.


References

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    Thapar A, Cooper M, Eyre O, Langley K. Practitioner Review: What have we learnt about the causes of ADHD? Journal of Child Psychology and Psychiatry. September 2012:3-16. doi:10.1111/j.1469-7610.2012.02611.x
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    PURPER-OUAKIL D, RAMOZ N, LEPAGNOL-BESTEL A-M, GORWOOD P, SIMONNEAU M. Neurobiology of Attention Deficit/Hyperactivity Disorder. Pediatric Research. May 2011:69R-76R. doi:10.1203/pdr.0b013e318212b40f
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    Arnsten AFT. ADHD and the Prefrontal Cortex. The Journal of Pediatrics. May 2009:I-S43. doi:10.1016/j.jpeds.2009.01.018
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    Linnet KM, Dalsgaard S, Obel C, et al. Maternal Lifestyle Factors in Pregnancy Risk of Attention Deficit Hyperactivity Disorder and Associated Behaviors: Review of the Current Evidence. AJP. June 2003:1028-1040. doi:10.1176/appi.ajp.160.6.1028
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    Kuehn BM. Increased Risk of ADHD Associated With Early Exposure to Pesticides, PCBs. JAMA. July 2010:27. doi:10.1001/jama.2010.860
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    Russell AE, Ford T, Russell G. Socioeconomic Associations with ADHD: Findings from a Mediation Analysis. Eapen V, ed. PLoS ONE. June 2015:e0128248. doi:10.1371/journal.pone.0128248
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    Pheula GF, Rohde LA, Schmitz M. Are family variables associated with ADHD, inattentive type? A case–control study in schools. Eur Child Adolesc Psychiatry. February 2011:137-145. doi:10.1007/s00787-011-0158-4
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    Tarver J, Daley D, Sayal K. Attention-deficit hyperactivity disorder (ADHD): an updated review of the essential facts. Child Care Health Dev. April 2014:762-774. doi:10.1111/cch.12139
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    Sheridan M, Drury S, McLaughlin K, Almas A. Early Institutionalization: Neurobiological Consequences and Genetic Modifiers. Neuropsychol Rev. November 2010:414-429. doi:10.1007/s11065-010-9152-8
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    Millichap JG, Yee MM. The Diet Factor in Attention-Deficit/Hyperactivity Disorder. PEDIATRICS. January 2012:330-337. doi:10.1542/peds.2011-2199
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    Bloch MH, Mulqueen J. Nutritional Supplements for the Treatment of ADHD. Child and Adolescent Psychiatric Clinics of North America. October 2014:883-897. doi:10.1016/j.chc.2014.05.002
  13. 13.
    Nigg JT, Lewis K, Edinger T, Falk M. Meta-Analysis of Attention-Deficit/Hyperactivity Disorder or Attention-Deficit/Hyperactivity Disorder Symptoms, Restriction Diet, and Synthetic Food Color Additives. Journal of the American Academy of Child & Adolescent Psychiatry. January 2012:86-97.e8. doi:10.1016/j.jaac.2011.10.015
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    Milich R. Sugar and hyperactivity: A critical review of empirical findings. Clinical Psychology Review. 1986:493-513. doi:10.1016/0272-7358(86)90034-6
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    Wolraich ML. The Effect of Sugar on Behavior or Cognition in Children. JAMA. November 1995:1617. doi:10.1001/jama.1995.03530200053037
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    Kim Y, Chang H. Correlation between attention deficit hyperactivity disorder and sugar consumption, quality of diet, and dietary behavior in school children. Nutr Res Pract. 2011:236. doi:10.4162/nrp.2011.5.3.236
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