Aug. 25, 1998 BOSTON, Aug. 24 -- The first direct evidence that a tobacco-specific cancer-causing substance is transmitted to developing fetuses when a pregnant woman smokes was revealed here today, at a national meeting of the American Chemical Society, the world's largest scientific society. The University of Minnesota Cancer Center scientist who conducted the study called the finding "an unacceptable risk."
Some 61% of smoking women who become pregnant do not quit smoking during pregnancy, according to a study published in the American Journal of Public Health (May 1990, Vol. 80, No. 5, pp. 541-544).
In a first-of-its-kind study, Stephen S. Hecht, Ph.D., found by-products of the nicotine-derived chemical NNK in the first urine of babies born to smoking mothers. NNK is unique to tobacco and is one of the strongest carcinogens in tobacco smoke. This study suggests it is not only taken in, but processed by the fetus, Hecht said.
Leslie L. Robison, Ph.D., who coordinates epidemiological studies nationwide for the Children's Cancer Group and is the Associate Director for Population Sciences at the University of Minnesota Cancer Center, says studies on smoking during pregnancy have been inconclusive regarding childhood cancer. But he says, "to identify the carcinogens in the urine of a newborn is a major documentation of the potential role and the transmission of those compounds" that should give epidemiologists greater incentive for further study.
Blinded samples of the first urine from 48 babies, both from smoking and non-smoking mothers, were sent to Hecht by collaborators in Germany*. Using a customized gas chromatography system, Hecht's laboratory found no NNK-metabolites in newborns of non-smokers but detected them in 22 of 31 samples from newborns whose mothers smoked during pregnancy.
"The results demonstrate that uptake of NNK by non-smokers begins before birth," says Hecht. He says this is particularly significant because most women who smoke during pregnancy continue to smoke afterward, exposing their children to this carcinogen for many years.
Levels of NNK by-products in the babies were about 10% as great as in the urine of adult smokers. Hecht says this is "substantial when one considers that exposure of the developing fetus to NNK would have taken place throughout pregnancy."
Last year Hecht reported the first evidence that NNK is found in non-smoking adults exposed to secondhand smoke in the workplace.
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