CHAPEL HILL - Five years ago, Dr. Denise B. Kandel, professor of psychiatry and public health at Columbia University, published a study suggesting that nicotine in the blood of pregnant women who smoked made it more likely that their daughters also would smoke when they reached adolescence or beyond.
The idea was that a biological mechanism kicked in that sensitized unborn babies to nicotine. Now, working with Dr. Richard Udry, Kenan professor of maternal and child health and sociology at the University of North Carolina at Chapel Hill, Kandel has found that's apparently not true.
Instead, the two have discovered that higher levels of testosterone -- the so-called "male" hormone -- in pregnant smokers somewhat predisposed their daughters to smoke themselves as they got older. The effect was above and beyond the widely accepted principle that children will mimic parents' behaviors to varying degrees as they age.
A report on the findings appears in the September issue of the American Journal of Public Health. "From a basic science point of view, we think this is an important finding because it wasn't known before that testosterone had this effect," Udry said. "From a practical point of view, it may be less important because there's nothing you can do about it, and you probably wouldn't want to do anything even if you could." Smoking during pregnancy is obviously a bad idea because it contributes to premature delivery and low-birth-weight babies, he said, not to mention its harmful effects on the heart, lungs and blood vessels. "At least this is one less thing for young women who smoke to worry about," Udry said. "You don't have to think about your prenatal smoking causing your daughter to smoke."
The new study came about after Udry read Kandel's first paper and knew that data from frozen blood samples collected from mothers in the early 1960s would enable them to test Kandel's hypothesis about a nicotine-prompted smoking "trigger." Also available was extensive interview information from pregnant women and, more recently, from their daughters when they reached their mid-teens and late 20s.
The frozen blood samples, which tests showed remained in good condition for more than 30 years, revealed both testosterone during pregnancy and levels of cotinine, a byproduct of nicotine indicative of how much a person smokes. Kandel and Udry found no correlation between prenatal cotinine levels in mothers and daughters' later smoking. They did uncover a distinct correlation, however, between mothers' testosterone and daughters' smoking. Researchers analyzed information from 240 pairs of mothers and daughters involved in research known as the Child Health and Development Study. They controlled statistically for the daughters' smoking in imitation of their mothers.
There is no evidence that smoking increases testosterone in humans or animals but may decrease the hormone somewhat, Udry said. Mechanisms underlying relationships of prenatal testosterone with mothers' and daughters' smoking are unknown. Blood samples, which came from California Kaiser Permanente patients, have been and continue to be used in numerous other studies, including work on cancer and environmental toxins to which the pregnant women may have been exposed.
"The effects of nicotine or continine on testosterone and the role of smoke compounds and nicotine metabolites other than continine need to be better understood before the hypothesis of an effect of exposure to prenatal maternal nicotine on offspring smoking is discarded," Kandel and Udry wrote.
Note: Udry can be reached at 919-966-2829, Kandel at 212-568-2570.
News Services Contact: David Williamson, 919-962-8596.
Journal
American Journal of Public Health