TUESDAY, Dec. 3, 2013 (HealthDay News) -- A new study from
Australia sheds more light on what environmental factors might
raise the risk for attention-deficit/hyperactivity disorder
"Compared with mothers whose children did not have ADHD, mothers of children with ADHD were more likely to be younger, single, smoked in pregnancy, had some complications of pregnancy and labor, and were more likely to have given birth slightly earlier," said study co-author Dr. Carol Bower, a senior principal research fellow with the Center for Child Health Research at the University of Western Australia. "It did not make any difference if the child was a girl or a boy."
The researchers did find that girls were less likely to have
ADHD if their mothers had received the hormone oxytocin to speed up
labor. Previous research had suggested its use during childbirth
might actually increase the risk of ADHD.
The causes of ADHD remain unclear, although evidence suggests
that genes play a major role, said Dr. Tanya Froehlich, an
associate professor at Cincinnati Children's Hospital Medical
"Many prior studies have found an association between ADHD and [tobacco and alcohol exposure in the womb], prematurity and complications of pregnancy and delivery," she said.
One thing is certain: Diagnoses of ADHD have become common in
the United States. A survey released in November found that 10
percent of American children have been diagnosed with the
condition, although the rapid increase in numbers seems to have
ADHD is more prevalent in boys. Its symptoms include
distractibility, inattention and a lack of focus.
In the new study, researchers examined the medical records of
nearly 13,000 children and young adults who were born in Western
Australia and took stimulant medications for ADHD between 2003 and
2007. Stimulant drugs such as Ritalin and Adderall are typically
used to treat ADHD.
The researchers compared the subjects to more than 30,000 other
children to see if there were any environmental differences.
Although factors such as a mother's younger age and smoking
during pregnancy were linked to a higher risk of ADHD in children,
"low birth weight, birth at greater than full term and breathing
difficulties in the baby were not more common [in the ADHD group],"
What's going on?
"Chronic exposure to smoking in pregnancy may create an imbalance in chemicals that result in ADHD," said study lead author Desiree Silva, a professor of pediatric medicine at the University of Western Australia.
But Froehlich said the picture may be even more complicated.
Some researchers have suggested that "people with ADHD are more
likely to smoke, and then may pass on their ADHD-related genes to
their children," Froehlich said.
Urinary tract infections also are thought to contribute to
inflammation that affects the development of the brain in the
fetus, she said. Stress during pregnancy -- perhaps from being
single or a young mother -- could do the same thing.
"[However], since ADHD is associated with higher rates of teen pregnancy, it is also possible that the younger and single mothers themselves have higher rates of ADHD, and they are passing on their ADHD-related genes to their children," Froehlich said.
The Australian researchers called for more study on the
The study appears online Dec. 2 and in the January print issue
of the journal
For more about
ADHD, visit the U.S. National Library of Medicine.
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