Attention deficit hyperactivity disorder (ADHD) is one of the most common neurobehavioral disorders in children. New research is looking for answers as to why.

One study reveals an association between oxygen deprivations in the womb and ADHD, according to Kaiser Permanente’s study in the Pediatric Journal. A second new study suggests there has been a rise in the rate children are being diagnosed with ADHD.

In 2011 over 5 million children in the U.S. had the disorder, according to the Center for Disease Control and Prevention.

“As with many health problems, it can be difficult for individuals to recognize symptoms and gather resources to help. Currently the rate of ADHD treatment in this country does not seem excessive. The significant increase in rates of diagnosis seems to be within ethnic minorities. This is likely positive because they have been much less likely in the past to be treated for ADHD,” James Terfruchte, psychiatrist at Student Health Services, said.

Terfruchte added some common symptoms of ADHD sufferers. They include difficulty sustaining attention, difficulty persisting on tasks, restlessness, distractibility, poor impulse control, forgetfulness and difficulties with organization.

Steven Landau, professor of psychology, said there is no known cause for ADHD, however genetics are a factor. He said about one third of all children with ADHD have at least one parent with the disease.

Some other factors that are considered risk factors for ADHD according to Landau are maternal nicotine and alcohol use while pregnant. He also said some studies suggest exposure to lead can be a factor.

“Personally I think ADHD is present during the first trimester of a women’s pregnancy,” Landau added.

Terfruchte agreed with the finding of the Kaiser Permanente study that said experiences during pregnancy or birth that lead to oxygen deprivation can cause a higher risk, of about 16 percent, to be born with ADHD. Some examples of experiences that can occur are birth asphyxia, neonatal respiratory distress syndrome and preeclampsia.

Children who are born breech or transverse, meaning feet or shoulders first, or whose birth involved cord complications were at a 13 percent higher risk of ADHD, according to the Kaiser Permanente study.

“There is no consistent research findings on what is different in the brain of those with ADHD, however it is an imbalance of brain chemistry,” Landau explained.

Landau added that it is never too late to be diagnosed, however he is opposed to treating ADHD before pre-school age. According to the DSM-4, children should be diagnosed before age 7.

If someone is questioning whether they have ADHD they should discuss the issue with their healthcare provider, according to Terfruchte. He also said to remember substance abuse can cause similar symptoms to ADHD.