Adolescent girls who were exposed to tobacco smoke while in the womb are more likely to take up smoking and become dependent on tobacco than their peers without this exposure, a new study finds.
"[S]ymptoms of nicotine dependence and progression in tobacco use in adolescent girls can be linked with nicotine exposure in utero," the researchers write.
They note that the associations remained "robust" after taking into account several potential confounding factors, including parents' social position and postnatal tobacco use. Tobacco dependence "should be added to the risks of passive exposure during the prenatal life," conclude Mina Rydell, MSc, from the Department of Public Health Sciences, Division of Epidemiology, Karolinska Institutet, Stockholm, Sweden, and colleagues.
Their study is published in the March issue of the British Journal of Psychiatry.
Brain Priming Effect
Nicotine crosses the placenta barrier and can result in even higher fetal concentrations than maternal concentrations, the authors note in their report.
"Research in both animals and human cell systems have indicated that prenatal nicotine exposure might result in a brain priming effect, where the exposed fetus might be more vulnerable to tobacco dependence following tobacco use later in life," Rydell told Medscape Medical News.
However, results from previous epidemiological studies have been "inconsistent, and there is a distinctive lack of prospective longitudinal studies," she noted.
The new findings stem from a prospective longitudinal study involving 3020 Swedish youths who were followed from about the ages of 11 to 18 years. Tobacco use was assessed at baseline (age 11) and 6 more times during follow-up via a self-administered questionnaire. The annual participation rate ranged from 87% to 96%, with 69% of the adolescents participating in all assessments.
About 27% of these young people were prenatally exposed to maternal tobacco smoke, and 43% were prenatally exposed to any parental tobacco use. During follow-up, 1007 children started using tobacco (41.7% of those exposed to prenatal maternal tobacco use, compared with 30.6% of those unexposed), of which 761 started smoking daily (33.7% of those exposed to prenatal maternal tobacco and 22.2% of those unexposed).
The corresponding figures for current snus (Swedish smokeless tobacco) use were 38.3% of those exposed and 29.2% of those unexposed; the figures for those who took up daily snus use were 34.1% and 24.8% for those exposed and unexposed, respectively.
2-Fold Increased Risk
At age 17 years, girls who were prenatally exposed to mom's tobacco and who took up smoking had roughly a 2-fold higher likelihood of both heavy tobacco use (5 or more cigarettes or snus dips per day; adjusted odds ratio [OR], 1.93; 95% confidence interval [CI], 1.30 - 2.86) and a strong craving for tobacco (adjusted OR, 2.04; 95% CI, 1.28 - 3.32).
They also had a 2- to 3-fold higher likelihood of experiencing a high number of withdrawal symptoms (at least 4 vs fewer than 4 symptoms; adjusted OR, 2.83; 95% CI, 1.68 - 4.87).
These associations were weaker among boys and did not reach statistical significance, which "adds strength to the hypothesis of a stronger vulnerability of the female fetal brain to nicotine neurotoxicity," the authors say. Similar sex differences have been reported in animal studies.
"There are growing indications not only that girls are more vulnerable to prenatal nicotine exposure but also that this difference concerns measures of nicotine dependence, as opposed to uptake of tobacco, which is rather influenced by social factors," Ms. Rydell said.
