by Nancy Walsh

Both maternal and paternal cigarette smoking can contribute to adverse chronic conditions — physical and psychological — in children, two large studies found.

Writing in the July issue of Pediatrics, Marie-Jo Brion, PhD, of the University of Bristol in England, and colleagues reported that children in two cohorts whose mothers smoked were more likely to have conduct/externalizing behavior problems than were those who had no prenatal tobacco exposure:

* British cohort, OR 1.24 (95% CI 1.07 to 1.46, P=0.005)
* Brazilian cohort, OR 1.82 (95% CI 1.19 to 2.78, P=0.005)

In a second study in the same issue, Chinese researchers found that daily paternal pre- or postnatal smoking was associated with increased mean body mass index (BMI) Z-scores in offspring at seven years, with a mean difference of 0.10 (95% CI 0.02 to 0.19) and also at 11 years, when the mean difference was 0.16 (95% CI 0.07 to 0.26).

These studies “tighten the evidence around tobacco smoke exposure and chronic conditions of childhood,” observed Jonathan P. Winickoff, MD, of Massachusetts General Hospital for Children in Boston, and colleagues in an editorial accompanying the studies.

Winickoff and colleagues wrote that these studies contribute to a growing body of research findings linking tobacco smoke exposure and multiple childhood morbidities and mortality, ranging from miscarriage, stillbirth, and sudden infant death syndrome to decreased lung function and obesity.

Brion and colleagues sought to determine if maternal smoking also could be causally related to the widely reported psychological problems seen in offspring.

Their study included 6,735 children residing in southwest England born between April 1991 and December 1992, as well as 509 children from the city of Pelotas in southern Brazil who were born during 1993.

The prevalence of maternal smoking was almost twice as high in the Brazilian cohort (29.4% versus 15.9%), but consistency was observed otherwise in the two groups.

In unadjusted models, maternal smoking was associated with behaviors in children at four years of age including inattention/hyperactivity, conduct/externalizing problems, and peer/social difficulties, but not with emotional/internalizing problems.

After adjusting for multiple potential confounders, however, such as birth weight and gestational age, socioeconomic factors, and maternal-paternal smoking, only conduct/externalizing problems were seen in both cohorts.

These findings support the concept that these children’s behavioral problems may be mediated by the influence of intrauterine tobacco exposure, and particularly nicotine, on neurodevelopmental pathways, according to the investigators.

They acknowledged that the study had shortcomings. Information about potentially important confounders, such as maternal antisocial behavior, was not available, and different instruments were used to assess child behavior in the two cohorts.

Also, parental smoking was measured by self-report, which may represent an underestimation.

In the second study, C. Mary Schooling, PhD, and colleagues from the University of Hong Kong, examined the effects of secondhand smoke on 6,790 children born during 1997 whose mothers did not smoke, stratifying them according to degree of paternal smoking.

They found that children of daily paternal smokers were from lower socioeconomic backgrounds, had mothers not born in Hong Kong, and were less likely to be breastfed.

Unlike BMI, the children’s height was not affected by paternal smoking.

At age seven, the difference in height Z-scores was −0.01 (95% CI −0.08 to 0.06), and at age 11 the difference was 0.02 (95% CI −0.05 to 0.10).

“To date, most of the evidence for the association between parental smoking and offspring overweight comes from Western or long-term developed settings, where smoking and childhood BMI are socially patterned and usually associated with low socioeconomic position,” the investigators wrote.

They noted that in Hong Kong, few women smoke and about one-quarter of men do, and although the prevalence of overweight in childhood is comparable to that in Western countries, it may be less socially patterned.

“Therefore, currently developed Hong Kong may serve as an ideal, non-Western social laboratory in which to verify associations from Western societies that are potentially confounded by [socioeconomic position],” they wrote.

In this study, the data were collected prospectively but there still were limitations. Secondhand smoke exposure was determined by parental report, so underreporting was possible, and childhood adiposity was measured by proxy using BMI, which does not differentiate between body fat and lean mass.

Nonetheless, the study suggests that paternal smoking may contribute to excess weight in offspring. Possible explanations for this include the fact that infants in households of smokers were less likely to be breastfed, and parents may have been generally less health-conscious.

“Alternatively, our findings might reflect the physiologic effects of paternal smoking and perhaps prenatal [secondhand smoke] exposure,” they wrote.

For example, while nicotine exposure from secondhand smoke might not be sufficient to cause intrauterine growth restriction, it might lead to restricted brain development and changes in appetite and metabolism.

In the editorial, Winickoff and colleagues urged continuation of efforts to curb smoke exposure in workplaces, restaurants, homes, and cars, recommending that clinicians utilize office systems, family-centered approaches, and community outreach to further minimize exposures and improve the health of both parents and children.

“Parental tobacco dependence, itself a chronic condition, begets other chronic conditions of childhood,” they wrote.

Nancy Walsh is a MedPage Today contributing writer.

Originally published in MedPage Today. Visit MedPageToday.com for more smoking news.