From the Pulmonary Section, Baylor College of Medicine and Texas Children’s Hospital.
CORRESPONDENCE TO: Harold J. Farber, MD, MSPH, FCCP, Pulmonary Section, Baylor College of Medicine and Texas Children’s Hospital, 6701 Fannin, Ste 1040, Houston, TX 77030; e-mail: firstname.lastname@example.org
FINANCIAL/NONFINANCIAL DISCLOSURES: The author has reported to CHEST the following conflicts of interest: Dr Farber receives salary support for service as Associate Medical Director for Texas Children’s Health Plan and travel support for service on the Executive Committee of the American Academy of Pediatrics Section of Tobacco Control.
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.
Tobacco is unique among heavily promoted consumer products in that it causes disease and death when used exactly as intended. The development of the mass-produced cigarette with its aggressive promotion and addictive potential led, in the 20th century, to the rapid escalation of the tobacco epidemic and tobacco-caused disease. With aggressive promotion to adolescent and young adult women in the mid-20th century forward, the prevalence of tobacco smoke exposure and tobacco dependence among women of childbearing age rapidly escalated and, from that, the in utero tobacco product exposure of their children.
In recent years, the effects of in utero tobacco smoke exposure have become increasingly well recognized. The effects on prematurity, low birth weight, and sudden infant death syndrome were recognized in the 2006 US Surgeon General Report.1 Lasting adverse consequences of fetal nicotine exposure on brain development were recognized in the 2014 US Surgeon General Report.2 A growing body of research is demonstrating that the harms of in utero tobacco smoke exposure extend well beyond infancy.
The Generation R study is a long-term prospective follow-up study of mothers and their children from pregnancy forward. Previously reported findings from this study have shown an effect of in utero smoke exposure on wheezing when the cohort was assessed at 3 and 4 years of age.3 In this issue of CHEST (see page 607), den Dekker et al4 extend these findings to demonstrate that continued smoking through pregnancy (after the first trimester) is associated with increased risk for persistent wheezing and physician-diagnosed asthma when the children were assessed at 6 years of age. These results build on a growing body of evidence showing that in utero tobacco smoke exposure has long-lasting effects on asthma risk. In a cross-sectional assessment of Latino and African American subjects with asthma in five sites in the United States and Puerto Rico, risk for poorly controlled asthma at 8 to 21 years of age was substantially greater if there was a history of in utero tobacco smoke exposure.5 Maternal exposure to secondhand smoke during pregnancy has been shown to increase asthma risk in her children.6
Is the effect of in utero tobacco smoke exposure on asthma risk due to nicotine, or is it from other components of tobacco smoke? Tobacco smoke is a complex mix of thousands of toxic and carcinogenic substances. Nicotine crosses the placental barrier rapidly. In the mouse, nicotine exposure during gestation stimulates branching morphogenesis of the airways, reduces forced expiratory flows, increases airway reactivity, and increases collagen deposition around airways. These effects appear to be mediated by the α7 nicotinic acetylcholine receptor, as these effects are not seen if the receptor is blocked.7 Perinatal nicotine exposure has also been shown to effect DNA methylation patterns and histone acetylation and thereby gene expression and lung function in a heritable manner.8 Although not excluding harms from other tobacco-related toxins, these laboratory animal studies show that the nicotine component of tobacco smoke is important in causing the adverse impacts on lung development and increasing risk for wheezing illness and asthma.
New nicotine delivery systems, such as electronic cigarettes, are rapidly rising in popularity among young people.9 These electronic nicotine delivery systems appeal to adolescents who would not otherwise use combustible tobacco.10 That in utero nicotine exposure can lead to substantial and potentially heritable harms raises great concern about the heavy promotion and rising popularity of electronic nicotine delivery systems among adolescents and young adults of childbearing age.
Does the damage caused by nicotine and tobacco smoke exposure stop at birth? The results reported by den Dekker et al4 in this issue did not find an association of paternal smoking of five or more cigarettes per day associated with children’s asthma. Paternal and maternal smoking, however, are not equivalent. The Lowering Environmental Tobacco Smoke: LET’S Manage Asthma study found that among children with asthma and tobacco smoke exposure, the urine cotinine to creatinine ratio—a validated biomarker of tobacco smoke exposure—was much greater if the mother or caregiver was a smoker as opposed to another source of exposure.11 The Chicago Initiative to Raise Asthma Health Equity (CHIRAH) study, in a sample of children 8 to 14 years old, found that having a detectable salivary cotinine level was associated with increased risk for asthma exacerbation.12 Population-based studies have shown that adoption and implementation of smoke-free legislation reduces asthma hospitalization rates for children.13 Although gestation is a particularly vulnerable time for pulmonary development, the effects of tobacco smoke exposure on respiratory problems of children continue well beyond birth. Tobacco and nicotine exposure harms children from gestation forward.
There is a large evidence base for effective tobacco control programs and policies,14 yet most of the recommendations have not been implemented. Although progress has been made since the peak of the tobacco epidemic in the mid-20th century, 42 out of 50 states in the United States and the federal government received a failing grade on tobacco prevention and control from the American Lung Association in 2015.15 If politicians and policy advocates truly care about protecting children’s life, health, and ability to breathe from gestation forward, they will put greater efforts and resources into effective tobacco control.
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