Although some people may not be diagnosed with ADHD until adulthood, their condition has been present since they were children. ADHD runs in families, but certain environmental factors such as exposure to alcohol or nicotine during pregnancy or lead during early childhood may trigger this disorder.
Heredity
In a report published in 2000, the American Academy of Pediatrics stated that having a close relative who suffers from ADHD increases the chance of a person being diagnosed with ADHD. Having a sibling with ADHD increases the chance of being diagnosed with this disorder by 20 to 25 percent. Yet, having an identical twin diagnosed with ADHD increases the chance of being diagnosed to 70 to 80 percent. Since identical twins have the same exact genes, if ADHD was purely a genetic disorder then all identical twins of ADHD patients should share the condition. Thus, besides genetics, environmental factors also play a role in acquiring ADHD, states Dr. Dee McKeel in a study published in the "Genetics in Human Affairs" journal in June 2003. The National Collaborating Centre for Mental Health estimates that genetics plays a role in 75 percent of the ADHD cases.
Prenatal Factors
People with ADHD are approximately two times as likely to have been exposed to alcohol or cigarette smoke during the pregnancy, says AboutKidsHealth.com. They are also more likely to have been born prematurely or with a low birthweight. Many people with ADHD needed medical help during the newborn period, as well. Many of them had surgeries or needed extra oxygen. Such factors account for 10 to 25 percent of the risk of developing ADHD, even if it did not become apparent until years later.
Environmental Toxins
The first studies stating that several toxins can increase a person's likelihood of being diagnosed with ADHD later in life were published in the 1970s. Among the first such studies was one by Dr. Oliver David, who discovered high concentrations of lead in children with ADHD in 1972. Lead exposure has not been as common since the 1970s, when lead gasoline and lead paint were banned in the United States. Some lead can still be found in the plumbing and paint of old buildings, as well as some consumer products such as cheap jewelry. Another environmental toxin that has been linked to ADHD is polychlorinated biphenyls, or PCBs. This industrial chemical was also banned in the 1970s but it stays in the environment for a long time, and a person can be exposed to it, for example, by eating fish and fatty foods. Although environmental toxins may increase a person's likelihood of acquiring ADHD, it is not likely to be a main factor.
References
- "Lancet"; Lead and hyperactivity; David, Clarke, Voeller; Vol .2; 1972
- "Pediatrics"; Clinical practice guidelinest; American Academy of Pediatrics; Vol. 105; 2000
- National Collaborating Centre for Mental Health: Diagnosis and management of ADHD in children, young people and adults
- AboutKidsHealth: Environmental Factors in ADHD
- "Genetics in Human Affairs": Genetics and ADHD
