When mom or dad puffs on a cigarette, their infants may inhale the resulting second-hand smoke. Now, scientists have detected cancer-causing chemicals associated with tobacco smoke in the urine of nearly half the babies of smoking parents.

"The take home message is, 'Don't smoke around your kids,'" said Stephen S. Hecht, Ph.D., professor and Wallin Chair of Cancer Prevention at The Cancer Center at the University of Minnesota.

According to a study of 144 infants, published in the May issue of Cancer Epidemiology, Biomarkers & Prevention, Hecht and his colleagues found detectable levels of NNAL* in urine from 47 percent of babies exposed to environmental tobacco carcinogens from cigarette smoking family members. NNAL is a cancer-causing chemical produced in the human body as it processes NNK**, a carcinogenic chemical specific to tobacco.

"The level of NNAL detected in the urine of these infants was higher than in most other field studies of environmental tobacco smoke in children and adults," Hecht said.

"NNAL is an accepted biomarker for uptake of the tobacco-specific carcinogen NNK. You don't find NNAL in urine except in people who are exposed to tobacco smoke, whether they are adults, children, or infants."

A previous study by Hecht and his colleagues indicated that the first urine from newborns whose mothers smoked during pregnancy contained as much as one-third more NNAL compared to the babies in the current study. The newborn infants, however, took in the carcinogen directly from their mothers through their placentas rather than by breathing second-hand smoke in the air in their family homes and cars.

In the current study, when babies had detectable levels of NNAL, Hecht said that family members smoked an average of 76 cigarettes per week, in their home or car while the babies were present. In children of smokers whose babies had undetectable levels of NNAL in their urine, the average number of cigarettes smoked by family members was reported at 27 per week.

"With more sensitive analytical equipment, the NNAL from urine of babies in lower frequency cigarette smoking households would most likely be detectable," Hecht said.

While studies have not determined how the long term risk of exposure to cancer-causing tobacco smoke affects the genetics of babies during their early years when they are growing rapidly, Hecht said that this study demonstrated substantial uptake of NNK and its metabolite NNAL in infants exposed to environmental tobacco smoke.

"These findings support the concept that persistent exposure to environmental tobacco smoke in childhood could be related to cancer later in life," he said.