What Causes ADHD?

Epigenetics and ADHD: The Impacts of Environment, Lifestyle, and Stress

ADHD is a genetic disorder, but DNA is not working alone. Stress, foods, and environmental toxins change the brain as well. Here, learn how to reverse their negative effects.

Harmonyx Releases Genetic Test for ADHD Medication
Harmonyx Releases Genetic Test for ADHD Medication

What Causes ADHD?

Our understanding of ADHD has grown by leaps and bounds over the past 30 years. What started as hyperkinetic impulse disorder — its primary symptom excessive hyperactivity — over time shifted to attention deficit disorder and a focus on problems with inattention, then to reward functioning, and later to executive functioning. None of these translations was wrong, in and of itself; each set of highlighted symptoms is a distinct and important part of the disorder we now call ADHD. But the facets were poorly integrated with one another, and thus painted an incomplete picture of a highly complex condition.

Now, researchers understand that ADHD is primarily a disorder of self-regulation. Self-regulation weaves together all the older theories of ADHD into one cohesive picture; it is also what allows humans to manage impulses, engage or disengage attention, and navigate between deliberate and automatic responses to different situations. The ability to self-regulate is managed across the brain in highly interconnected ways; similar brain nodes regulate both attention and emotion — and when one area isn’t performing well, the others suffer, too.

The newest theories of ADHD, then, don’t focus on a single “underperforming” area of the brain, as older ones did. It’s now understood that ADHD manifests when neurons misfire in the ever-shifting communications and connections between multiple areas of the brain. Emerging research also suggests that these neurological wrinkles may be driven by the environment as much (or more) than they are by genes.

This new framework provides a much more nuanced and complex view of ADHD, but it also provides hope: If ADHD symptoms can be worsened by environmental causes, they can be improved by them, too. Read on to find out how.

ADHD: from Genetics to Epigenetics

Researchers have long known that ADHD can be passed down genetically. But the idea that we can find the single gene responsible for ADHD and “fix” it is now understood to be outdated. The newest theory of ADHD, as a disorder primarily related to self-regulation, relies on something called epigenetics.

[Quiz: Can You Tell the Difference Between ADHD Myths and ADHD Facts?]

Epigenetics refers to biological traits or changes that cannot be explained by a person’s genetic code. Epigenetic mechanisms actually create a physical mark on the DNA when a person undergoes an important experience, whether it’s positive or negative. These marks — which can be added methyl molecules, or a modified histone tail — adjust the individual’s gene function, changing what the genes do or how strongly they express themselves. In a nutshell, environment and experiences affect a human’s development and behavior in an enduring fashion — actually altering regions of DNA, with effects that may last for an entire lifetime.

How does it work? It starts with genes — the building blocks of who we are and who we become. But beginning at conception, everyone is exposed to different environmental toxins and advantages — and after we’re born, psychological inputs like stress, adversity, and even trauma begin to factor in. Epigenetics takes this input and uses it to change how genes are expressed — meaning a gene’s output isn’t fully known until environment and personal history are factored in.

Environmental Effects on ADHD

Epigenetics paints a much more complicated view of ADHD, but also a much more optimistic one; genes do not solely determine an individual’s fate. In fact, while genes may make someone more prone to certain diseases or disorders, including ADHD, the entire genetic system is highly dynamic and responsive to input. This means it’s possible to change the expression of a person’s “ADHD genes” by making certain environmental changes.

Credible and robust epigenetics research confirms these assertions. One experiment1 took two genetically identical mice embryo and, during the prenatal stage, fed their mothers foods that included the toxin bisphenol-A (BPA). The food of one mouse’s mother, however, was supplemented with nutrients like choline, folic acid, and B12; that mouse was later able to avoid the negative effects of the BPA, including higher body fat index and a higher risk of cancer. This phenomenon can be explained by epigenetics — the additional nutrients were able to “turn off” the genes that respond to BPA, and thus protect the mouse from its harmful effects.

[Free Resource: What to Eat (and Avoid) for Improved ADHD Symptoms]

Another experiment2 — this one involving humans — tested whether taking an omega-3 supplement would impact the attention abilities of a mother’s child. The study found that children whose mothers had randomly received the supplement had stronger attention at 6 and 12 months, and later had better-developed mental abilities, than did children whose mothers had not taken the supplement. Since this experiment was randomized and the effect was so great, researchers were able to determine a causal effect — and again, one that was influenced by epigenetics. Food dyes, artificial preservatives, and lead yielded similar results3 — the introduction of each into a child’s pre- or post-natal environment had real, causal effects on his or her attention, hyperactivity, and emotional regulation.

Similar experiments have been done on stress and adversity — and how exercise can counteract those negative effects. One experiment4 placed rats into a stressful situation for a period of time each day, which resulted in significant epigenetic changes that decreased healthy function. However, when those same rats were also allowed to exercise — while still experiencing the stressor — the negative effects on the brain were completely eliminated. The study provided a clear example of how exercise can reverse the harmful brain-based effects of a negative early-life experience.

ADHD Research on Causes, Treatments

This research suggests that lifestyle changes may help to offset the effects of ADHD genes activated by genetic, chemical, food, or other factors. More epigenetic research is needed, however a few things are clear: Omega-3 supplementation, aerobic exercise, and stress management can have real, positive effects on ADHD symptoms in both children and adults.

How big are these effects? Some changes, like reducing the amount of TV a child watches each day, have very small effects on ADHD symptoms — only slightly noticeable in a family’s everyday life. Others, like increasing omega-3 intake or introducing an exercise regimen, have significantly larger effect sizes — up to twice or three times as large as reducing screen time.

Researchers now recommend that anyone with ADHD follows these strategies:

  1. Exercise. There is strong, convincing evidence that exercise benefits a child’s development and attention. In fact, exercise can reverse negative ADHD symptoms in adults as well. It should be a regular treatment strategy.
  2. Sleep. Sleep is necessary for rebuilding the brain and body, and for improving attention skills and promoting learning. Getting a proper amount of restful sleep can improve symptoms for anyone with ADHD.
  3. Stress management. ADHD contributes to stress for the whole family, and often creates an unhealthy cycle between parents and children, or between spouses. Learning how to manage stress as a family — either through mindfulness, self-care, or therapy — will stop or slow the negative epigenetic changes in the brain that worsen ADHD symptoms.

Continuing research is creating an ever-growing body of evidence regarding which lifestyle changes improve ADHD symptoms, and which are less useful. Though findings are still preliminary, the evidence is already strong enough to make them actionable. Simple changes, like exercising more or taking a fish oil supplement, can have real, lasting effects on an individual’s ADHD symptoms — in other words, genes do not seal your fate.

[Daily Exercise Ideas to Boost Focus]

Learn more in Dr. Nigg’s book, Getting Ahead of ADHD: What Next-Generation Science Says about Treatments That Work and How You Can Make Them Work for Your Child

Joel Nigg, Ph.D., is a member of the ADDitude ADHD Medical Review Panel.

1 Dolinoy DC, Huang D, Jirtle RL. “Maternal Nutrient Supplementation Counteracts Bisphenol A-Induced DNA Hypomethylation in Early Development.” PNAS, vol. 104, 2007, pp. 13056–13061.
2 Colombo, John, et al. “Maternal DHA and the Development of Attention in Infancy and Toddlerhood.” Child Development, vol. 75, no. 4, 2004, pp. 1254–1267., doi:10.1111/j.1467-8624.2004.00737.x.
3 Stevenson, J, et al. “The Role of Histamine Degradation Gene Polymorphisms in Moderating the Effects of Food Additives on Children’s ADHD Symptoms.” The American Journal of Psychiatry, vol. 167, no. 9, Sept. 2010, pp. 1108–1115.
4 Kashimoto, R.K., et al. “Physical Exercise Affects the Epigenetic Programming of Rat Brain and Modulates the Adaptive Response Evoked by Repeated Restraint Stress.” Behavioural Brain Research, vol. 296, 2016, pp. 286–289., doi:10.1016/j.bbr.2015.08.038.