Childhood Asthma/Tobacco Smoke

Introduction

Characteristics

Fate and Transport

Exposure Pathway

Methods for Monitoring in the Environment

Methods for Measuring Human Exposure

Strategies for Preventing or Controlling Exposure


Respiratory Harmful Effects

Deposition, Absorption, and Metabolism

Dose-Response Relationship

Organ Sites of Toxicity

Biomarkers

Risk Assessment/Risk Management Considerations

References

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Respiratory Harmful Effects of Environmental Tobacco Smoke on Child Respiratory System

Major Effects of ETS

  • Children raised in homes with smokers have more
    • Wheezing
    • Coughing
    • Sputum Production
    • Respiratory Illnesses
  • For children with asthma ETS exposure exacerbates symptoms and can cause an attack
  • A strong relationship is seen between mother’s active smoking and pulmonary problems with children
    • This relationship may occur in two ways
      • Maternal smoking affects lungs of fetus
      • Mothers physically closer to children postnatally, thereby exposing children to large dose of ETS
  • ETS toxicants with respiratory effects
    • Ammonia, formaldehyde, and sulfur dioxide are respiratory irritants
    • Acrolein, crotonaldehyde, formaldehyde and hydrogen cyanide affect mucocilliary function
    • If these compounds are in high enough concentration they can inhibit clearance of smoke particles

Evidence of in utero exposure to ETS

  • Chen (1994)—Study of 3285 infants in Shanghai whose mothers were nonsmokers, but were exposed to ETS during pregnancy and the infants were then exposed postnatally. Infants with lower birth weight showed increase in respiratory hospitalizations
  • Environmental Protection Agency report (1992) reviewed many articles about respiratory health effects to infants and children
    • Increased lung compliance in newborns
    • Pregnant rats exposed to MS during 5 to 20 day gestation had pups with reduced lung volume, number of lung saccules, and reduced length of elastin fibers in lung interstitium
    • Cord serum levels of IgE and IgD were higher neonates whose mothers smoked during pregnancy
  • Causal relationship between ETS exposure and reduction in airflow parameters (i.e. FEV—Forced Expired Volume) of lung function
  • This decreased lung function may be the result of exposure to ETS in utero and continued exposure postnatally

Asthma Induction

  • Burchfield et al. (1990)—Cross-sectional study of 8,000 children and adolescents showed odds ratio of about two in children with parental smoking or (maternal smoking greater than 10 cigarettes a day, Weitzman et al. (1990))
  • Martinez et al. (1992)—Longitudinal study of asthma incidence among 774 children up to 5 years old showed relative risk of 2.5 (95% CI = 1.4,4.6) when the mother smoked more than 10 cigarettes/day
  • Sherman et al. (1990)—Study of 770 school children found no effect of maternal smoking on prevalence of asthma at the beginning of the study or in the 11 years of follow-up
  • California EPA performed a meta-analysis of 37 studies in which all but three reported a risk ratio greater than 1.0 and the pooled risk ratio from exposure related to maternal smoking 1.60 (95% CI = 1.29-1.99) NOTE: Potential confounder in this analysis the smoking status of the children which was either omitted or unknown.

    Take home message—There is strong evidence that ETS may cause asthma, but this evidence may be questionable as some studies did not look at other variables such as in utero exposure to ETS and smoking status of children