Deficiencies in nutrition

It has been established conclusively that a small percentage of children are sensitive to dyes and other food additives, sugar, caffeine, etc. (Jacobson and Schardt, 1999, Diet, ADHD & Behavior, Center for Science in the Public Interest, Washington, DC).

Nutritional data has been well summarized in a review article (Burgess et al., 2000, Am J Clin Nutr 71:327-330). Children with ADHD have lower levels of key fatty acids. In fact, one study found that the lower the levels, the worse the symptoms. The possibility that fatty acid deficiency is a trigger for ADHD is especially plausible as nutrition scientists have recently demonstrated that the American diet is extremely deficient in omega-3 fatty acids. At the same time, ADHD diagnoses are rapidly increasing. More support for this idea comes from findings that breast-fed children have much lower levels of ADHD, and that until quite recently, infant formula contained NO omega-3 fatty acids. These findings are only correlational, and do not prove a conclusive connection.

However, creating a deficiency of omega-3 fatty acids in pregnant rats produces pups that are hyperactive and that have altered brain levels of dopamine in the same brain regions as seen in humans and other rat models of hyperactivity.

Smoking during pregnancy
The finding of another possible cause stemmed from the observation that children of women who smoked during pregnancy are more likely to be diagnosed with ADHD (Kotimaa et al., 2003, J Am Acad Child Adol Psychiatry 42, 826-833). Given that nicotine is known to cause hypoxia (too little oxygen) in the uterus, and that hypoxia causes brain damage, smoking during pregnancy could be an important contributing factor leading to ADHD. It may even help explain in part the increase in ADHD diagnoses, as the number of women smokers has increased. However, there are not nearly enough women smoking during pregnancy to account for all the ADHD diagnoses. It is also possibile that cause and effect could be confounded in this study, since many mothers who smoke during pregnancy may be ADHD suffers themselves; therefore the cause may simply be the shared genetic material of mother and child, rather than the mother's smoking.

Sleep apnea
There is also new evidence that brief pauses in breathing (apnea) during infancy may be a cause of ADHD. Dr. Glenda Keating of Emory University presented data at the Society for Neuroscience annual meeting in October 2004, showing that repetitive drops in blood oxygen levels in newborn rats similar to that caused by apnea in some human infants is followed by a long-lasting reduction in dopamine levels, associated with ADHD. Apnea occurs in up to 85% of prematurely born human infants. (ScienceDaily)

Head injuries
It has been known for some decades that head injuries can cause a person to experience and display ADHD-like symptoms.