Smoking in pregnancy raises ADHD (Attention Deficit Hyperactivity Disorder) risk for child
Women who smoke during pregnancy are nearly twice as likely to have
children with Attention Deficit Hyperactivity Disorder (ADHD), a new
study finds.
"This study serves to underline the fact that women who are pregnant
should stop smoking," said lead researcher Dr. Karen Markussen
Linnet, a pediatrician at Aarhus University Hospital in Denmark. "We
are not able to make a certain conclusion, but this study points out
that there is an association between smoking and ADHD."
Reporting in the August issue of Pediatrics, Linnet and her
colleagues used extensive data available from the Danish
government's longitudinal registers on nearly 4,000 children born
between 1991 and 1994. They compared the smoking habits of the
mothers of 170 children who were later diagnosed with ADHD - or
hyperkinetic disorder, as it's called in Europe - with 3,765 mothers
whose children were not hyperactive.
After controlling for low birth weight of babies, poor newborn
health status, young maternal age and low socioeconomic status,
smoking mothers were nearly twice as likely to have children with
ADHD than mothers who didn't smoke while pregnant. 59% of the
mothers of ADHD children smoked during pregnancy, compared to 35
percent of the mothers whose children did not have the disorder.
One important factor the researchers could not assess was whether
pregnant smokers had ADHD themselves, which might make them more
likely to smoke, and could be the reason for the higher number of
children in this group who were diagnosed with hyperkinetic
disorders.
"Nicotine acts as a stimulant, and young adults with hyperkinetic
disorders who are pregnant could be using nicotine as a stimulant,"
Linnet said. "But it is very difficult to adjust for this factor,
and it is important that we not make final conclusions."
Linnet said one strength of her study is that it is longitudinal,
meaning that women reported their smoking habits before their
children were diagnosed with ADHD. This avoids what is called
"recall bias," when women are asked about their smoking habits after
they learn that their children have ADHD and when their responses
could be skewed by their feelings about their children.
"This is a very interesting study. The authors have controlled for a
lot of confounding factors, and it is certainly biologically
plausible that smoking could damage the fetus - less oxygen is going
to the brain, nicotine itself is a poison, and lots of other studies
have found associations between smoking and poor cognitive
development," said Gary Giovino, a senior research scientist in the
department of cancer prevention, epidemiology, and biostatistics at
Roswell Park Cancer Institute in Buffalo, N.Y.
"There is strong reason to believe that smoking is a risk factor for
ADHD, but at this stage of research we certainly don't know for sure
because of genetics and environmental risk factors like use of drugs
and poor nutritional status," he added.