Secondhand Smoke Exposure Linked to Mental Disorders in Children

Deborah Brauser

December 15, 2010

December 15, 2010 — A higher level of salivary cotinine, a biomarker used to measure secondhand smoke (SHS) exposure, is associated with poorer mental health — particularly hyperactivity and conduct disorder — in children, suggests a new community-based study drawn from the Scottish Health Survey.

In addition, investigators found that 40% of the more than 900 children included in the study had high SHS exposure, with the highest cotinine levels found in those living in poorer areas.

"We know that secondhand smoke is linked to physical health outcomes in kids, but we know little about the mental health effects," lead study author Mark Hamer, PhD, associate professor of social epidemiology in the Department of Epidemiology and Public Health at University College London, United Kingdom, told Medscape Medical News.

Dr. Mark Hamer

However, he said, the results from this study were not surprising to him. "Animal data has suggested direct pathways between nicotine exposure and mental function. There are feasible biological mechanisms to explain the effects."

Exposure to SHS was highly prevalent in the children in this study, and Dr. Hamer noted they often have little control over this exposure because it is most prevalent in their own home.

"Smoking parents should be educated [by clinicians] about the harmful effects of secondhand smoke exposure on their kids," said Dr. Hamer.

The study was published online December 6 in the Archives of Pediatrics and Adolescent Medicine.

Higher SDQ Scores

In a study published earlier this year and reported by Medscape Medical News, Dr. Hamer and his colleagues assessed data on 5560 nonsmoking adults with no history of mental illness. They found that those with SHS exposure had a higher risk for psychological distress and a higher risk for future psychiatric hospitalization than did those with low SHS exposure.

For this study, they evaluated data from the 2003 Scottish Health Survey on 901 nonsmoking children between the ages of 4 and 12 years (mean age, 8.3 years).

Salivary cotinine levels were measured through the use of a gas chromatograph. The levels were then grouped into 4 quartiles: low SHS exposure (≤0.05 ng/mL; n = 101), low to moderate exposure (0.06-0.30 ng/mL; n = 280), moderate exposure (0.31-0.70 ng.mL; n = 159), and high exposure (>0.70 ng/mL; n = 361).

A subsample of participants 8 years and older (n = 524) also filled out self-reports on SHS exposure.

For all children, interviewers used the Strengths and Difficulties Questionnaire (SDQ) to assess psychological distress; measured height, weight, and body mass index; and collected demographic information using several instruments, including the Scottish Index of Multiple Deprivation.

Results showed that the children in the high SHS exposure quartile had significantly higher total SDQ scores compared with those in the low quartile (mean difference, 2.8; 95% confidence interval [CI], 1.6 – 3.9).

"There was also evidence of a dose-response effect across the cotinine group (P trend = .001)," write the researchers.

"Children with higher cotinine levels were more likely to live in areas of greater socioeconomic deprivation, be a resident in a single-parent household, and report asthma," they add.

The strongest associations between the SDQ subscales and cotinine levels were for hyperactivity and conduct disorder (P trend = .001 for both disorders).

Finally, the association between SDQ score and self-reported exposure in the home for the subsample of older children was "similar in magnitude" to that found in the highest cotinine exposure group (mean score, 9.5 vs 9.2).

"We found an association between SHS exposure and poor mental health as reflected by higher scores on the SDQ," write the study authors.

"Although smoke-free legislation has contributed to a successful secular decline in SHS exposure among children, the evidence suggests that those children living with smokers and in disadvantaged households continue to experience substantial contact with SHS," they add.

Dr. Hamer reported that his team is now "interested in lifestyle risk factors for mental health, so are presently pursuing several lines of investigation."

Big Impact

Dr. Douglas Ziedonis

"I thought this was an important study to really start to look at the effect of [SHS] exposure on mental health in children," Douglas Ziedonis, MD, MPH, professor and chair of the Department of Psychiatry at the University of Massachusetts Medical School and UMass Memorial Healthcare System in Worcester, told Medscape Medical News.

"This study was terrific in that it had some objective measures of cotinine levels, that they had a particular instrument in the [SDQ], and that they were able to look at the dose-ranging response," said Dr. Ziedonis, who was not involved with this study.

"The literature is clear that kids who are smokers have increased risk for psychiatric problems. What's important with this study is that even kids who aren't smokers are at risk."

When asked about the finding of the strong association between high SHS exposure and hyperactivity and conduct disorder, Dr. Ziedonis said, "These are the more common psychiatric problems" for children.

"If you think of nicotine as a low-level stimulant, things that would agitate and cause a little more stimulation, then that makes sense pharmacologically."

He added that "an important question on a study like this is: does chronic exposure to smoke cause etiologic changes in the brains of kids who are still developing that might make them more vulnerable to psychiatric disorders?"

Dr. Ziedonis noted that 44% of all cigarettes consumed in the United States are by people with psychiatric disorders. "So clearly there's something going on with the association.

"The causality mechanism has not been understood, but this kind of a paper makes you wonder: Could there be something going on even earlier with kids in their development from this exposure? Not only acutely because of the mild stimulation from nicotine, but also: what's really happening with the brain being pickled with this level of cotinine?

"How might there be epigenetic changes, particularly during this vulnerable time of brain development, which relate to the amygdala and frontal lobe, in particular, in kids? I think future research in this area would be very helpful and informative."

Study limitations, he noted, which were also cited by the study authors, included not knowing any information on the prenatal smoking situation. "The prenatal period also affects a lot of things, like low birth weight. So that could potentially be a factor."

Overall, Dr. Ziedonis said that "all clinicians should be thinking about these findings, including child psychiatrists. But the study has a much bigger impact on the general population.

"So, the generalists, the pediatricians, the obstetricians, the family doctors, the internists, they all need to give parents this information about the medical risks for their children as well as the new mental health finding because all of them are bad reasons for exposing children to smoking," he concluded.

The study and/or authors were supported in part by the British Heart Foundation, the National Institute for Health Research, the Medical Research Council, and a Wellcome Trust Career Development Fellowship. The Scottish Health Survey was supported by the Scottish Executive. The study authors and Dr. Ziedonis have disclosed no relevant financial relationships.

Arch Pediatr Adolesc Med. Published online December 6, 2010. Abstract

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