* Risk higher among children exposed during pregnancy
* Study needs to be replicated by other teams
By Julie Steenhuysen
CHICAGO, Aug 1 Children whose mothers had high
exposure to electromagnetic fields while pregnant may have an
increased risk of developing asthma, U.S. researchers said on
Monday in a study that adds to an ongoing debate.
Many prior studies have failed to consistently show that
chronic exposure to electromagnetic fields -- from power lines
and appliances such as microwaves ovens, hair dryers and vacuum
cleaners -- are harmful to human health.
But many of these studies required people to estimate their
exposure levels over several years, says Dr. De-Kun Li, senior
research scientist at the Kaiser Permanente in Oakland,
California, whose study appears in Archives of Pediatrics &
To get a more conclusive answer, Li designed a so-called
prospective study in which 801 pregnant women wore monitors
that measured their exposure to magnetic fields for 24 hours.
These monitors measured their exposure to low-frequency
magnetic fields from electronics such as microwaves, hair
dryers, fans, coffee grinders and fluorescent light bulbs,
power lines, and transformer stations.
It did not monitor exposure to higher frequency
electromagnetic fields generated by cellphones or cellphone
The team used medical records to follow the women's
children for 13 years. During the follow-up, 130 children, or
20.8 percent of study participants, developed asthma.
Most of these cases were diagnosed before age 5.
They then compared exposure levels during pregnancy to
rates of asthma and found that children whose mothers had the
highest exposure levels -- within the top 10 percent of women
in the study -- were 3.5 times more likely to develop asthma
than those who were in the bottom 10 percent.
The risk for children whose exposure was somewhere in the
middle -- between 10 percent and 90 percent -- was 75 percent
higher than for those in the lowest exposure group.
For the average population, Li said, children of women
whose exposure levels were in the range of the bottom 10
percent in the study would have about a 13.6 percent absolute
risk of developing asthma. Women whose exposure was in the
highest range would have about a 33 percent risk of having
children who developed asthma over the 13 year study period.
Some 13 percent of children under age 18 have asthma, which
is caused by malfunction of the respiratory organs and the
Li said it is not clear why exposure to power lines might
increase the risk of asthma, but he said there are several
He said a prior study by his team found high exposure to
electromagnetic fields increased the risk of miscarriages. And
some animal studies have suggested that electromagnetic field
exposure can affect immune response, which could increase the
risk of asthma.
Exposure to power lines has been fodder for significant
debate, and while many studies have found an effect of some
sort -- ranging from immune disorders and poor semen quality to
certain types of cancers -- Li said his study offers a stronger
argument that concerns about magnetic fields may affect human
"This really needs to be studied," Li said. He said there
have been a lot of dismissive attitudes about the health
effects of exposure to magnetic fields, and he hopes his study
-- which measured exposure levels ahead of time -- will
encourage others to look further.
Still, he concedes that his findings need to be replicated
by different scientists.
Li said if the findings are confirmed, it may offer new
strategies for preventing the chronic disease in children.
(Editing by Mohammad Zargham)