* Study linked exposure during pregnancy to asthma
* Critics say findings ignore major body of research
* Study would need to be replicated
By Julie Steenhuysen
CHICAGO, Aug 2 (Reuters) - Critics say a controversial new study that linked high exposure to electromagnetic fields during pregnancy to asthma in children is flawed and ignores many prior studies that suggest such exposures are harmless.
The study by researchers at Kaiser Permanente in Oakland, California, measured exposure levels to magnetic fields -- caused by things like power lines and microwave ovens -- in 801 pregnant women and followed their children.
They found mothers who had the highest exposure to magnetic fields were 3.5 times more likely to develop asthma than those in the study whose mothers had the lowest exposure levels.
But several experts are challenging the findings, which were published on Monday in the Archives of Pediatrics & Adolescent Medicine. [ID:nN1E7701IT]
"The strong conclusions drawn from this paper that magnetic field exposure in pregnancy increases the risk of asthma in offspring cannot be justified based on the evidence provided in the publication," Patricia McKinney, professor of pediatric epidemiology at the University of Leeds in Britain, said in a statement.
McKinney said the study ignores major scientific reviews that concluded there was not a "sufficiently strong case for any further investigation of this topic."
Exposure to power lines has been fodder for significant debate, and while some studies have found an effect of some sort -- ranging from immune disorders and poor semen quality to certain types of cancers -- few have held up.
De-Kun Li, senior research scientist at the Kaiser, said his study offers a stronger argument because most prior studies required people to estimate their exposure levels, which is nearly impossible to do.
To get a better estimate of exposure, Li designed a so-called prospective study in which pregnant women wore monitors that measured their exposure to magnetic fields for 24 hours.
These monitors measured 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. They did not monitor higher-frequency electromagnetic fields generated by cellphones or wireless networks.
The team 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.
Professor David Spiegelhalter of the University of Cambridge in Britain said the study has the advantage of having measured exposure to magnetic fields during pregnancy rather than relying on recall.
But he said the finding of increased cases of asthma appears to be "an afterthought" in a study that was originally designed to study miscarriage.
"This means that it is essential that the findings ... are replicated by other researchers."
Li agrees that his findings need to be replicated by different scientists.
He said there have been a lot of dismissive attitudes about the health effects of exposure to magnetic fields, and that he hoped his study -- which measured exposure levels ahead of time -- would encourage others to look further.
Some 13 percent of children under age 18 have asthma, which is caused by malfunction of the respiratory organs and the immune system. (Editing by Mohammad Zargham)