Tobacco and Public Health - TCSC Indonesia

JONATHAN M. SAMET 301
Investigations conducted throughout the world have demonstrated an increased risk
of lower respiratory tract illness in infants with parents who smoked (Strachan and
Cook 1997). These studies indicate a significantly increased frequency of bronchitis
and pneumonia during the first year of life of children with parents who smoked.
Strachan and Cook (1997) reported a quantitative review of this information, combining
data from 39 studies. Overall, the approximate increase in illness risk was 50 per
cent if either parent smoked, with an odds ratio for maternal smoking somewhat
higher, at 1.72 (95 per cent CI: 1.55, 1.91). Although the health outcome measures
varied somewhat among the studies, the relative risks associated with involuntary
smoking were similar, and dose–response relations with extent of parental smoking
were demonstrable. Although most of the studies have shown that maternal smoking
rather than paternal smoking underlies the increased risk of lower respiratory tract illness,
studies from China show that paternal smoking alone can increase incidence of lower
respiratory illness (Yue Chen et al. 1986; Strachan and Cook 1997). In these studies, an
effect of passive smoking has not been readily identified after the first year of life.
During the first year of life, the strength of its effect may reflect higher exposures consequent
to the time–activity patterns of young infants, which place them in proximity
to cigarettes smoked by their mothers.
Respiratory symptoms and illness in children. Data from numerous surveys demonstrate
a greater frequency of the most common respiratory symptoms: cough, phlegm, and
wheeze in the children of smokers (US Department of Health and Human Services
1986; Cook and Strachan 1997; National Cancer Institute 1999). In these studies, the
subjects have generally been schoolchildren, and the effects of parental smoking have
been examined. Thus, the less prominent effects of passive smoking, in comparison
with the studies of lower respiratory illness in infants, may reflect lower exposures to
secondhand smoke by older children who spend less time with their parents.
Cook and Strachan (1997) have conducted a quantitative summary of the relevant
studies, including 41 of wheeze, 34 of chronic cough, seven of chronic phlegm, and six
of breathlessness. Overall, this synthesis indicates increased risk for respiratory symptoms
for children whose parents smoke (Cook and Strachan 1997). There was even
increased risk for breathlessness (OR = 1.31, 95 per cent CI: 1.08, 1.59). Having both
parents smoke was associated with the highest levels of risk.
Childhood asthma. Exposure to secondhand smoke might cause asthma as a long-term
consequence of the increased occurrence of lower respiratory infection in early childhood
or through other pathophysiologic mechanisms, including inflammation of the
respiratory epithelium (Samet et al. 1983; Tager 1988). The effect of secondhand smoke
may also reflect, in part, the consequences of in utero exposure. Assessment of airways
responsiveness shortly after birth has shown that infants whose mothers smoke during
pregnancy have increased airways responsiveness, a characteristic of asthma, compared
with those whose mothers do not smoke (Young et al. 1991). Maternal smoking during