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Is there a link between Secondhand Smoke Exposure and Attention-Deficit/Hyperactivity Disorder (ADHD) in Children?

passive smoking concept, second hand smoking, involuntary smoking

Reviewer : Dr. Abid

Secondhand smoke (SHS) or passive smoking refers to accidental inhalation of smoke fumes if someone is smoking nearby. Firsthand smoking and secondhand smoking both can be very damaging and can cause serious health issues. Tobacco is extremely harmful, and burning nicotine products release harmful chemicals or toxins; these chemicals inhaled during smoking affect and harm the entire body of individual who smoke as well as other people around him.

Non-smoker are also exposed to these harmful toxins as they passively inhale tobacco smoke. Therefore, people exposed to secondhand smoke may also experience serious health conditions such as; cardiovascular disease, respiratory disease, increased risk of different types of cancers etc. Moreover, children who are exposed to SHS may suffer through health conditions such as; respiratory infections, frequent and more severe asthma attacks, ear infections, learning and behavioral problems etc.

Thus, SHS exposure is a serious health concern that can affect both adults and children. Health experts suggest that preventing exposure from tobacco smoke could be the only practical solution for encountering such risks.

What evidence is there that suggests this link?

Some recent studies suggested that maternal smoking during pregnancy was strongly associated with the development of attention-deficit/hyperactivity disorder (ADHD) symptoms in their children. Attention-deficit/hyperactivity disorder is a mental health disorder that can cause above-normal levels of hyperactive and impulsive behavior. People with ADHD may have trouble focusing their attention on a single task for a long period. It is characterized by a persistent pattern of inattention, hyperactivity-impulsivity or both. It is an impairing condition which is prevalent and creates a substantial burden for individuals and society.

Effect of smoke

When mothers inhale smoke from cigarettes, nicotine distilled from the tobacco is rapidly metabolized in the liver to a substance called cotinine, which may disrupt the maturation of the central nervous system resulting in later development of ADHD symptoms in their offspring.

 In China the prevalence of smoking among women is low, whereas among men it is high. Researchers suspected and hypothesized that SHS exposure may be an important environmental factor associated with ADHD in China, as studies suggested that approximately 40% of Chinese women have been exposed to SHS primarily in the home environment. It was also suspected that postnatal (after birth) SHS exposure may also induce ADHD deficits because the human brain continues to develop during the post-natal period. However, few studies have investigated the association between the exposure timings i.e prenatal (before birth), early post-natal and current period of SHS and ADHD symptoms and sub-types in children.

Research on second hand smoke

Therefore, researchers from China conducted studies with an objective to evaluate the associations of pre-natal, early post-natal, or current SHS exposure with ADHD symptoms and sub-types among school-aged children.

To conduct the studies a total of 45562 children, aged 6 to 18 years from elementary and middle schools in Liaoning province, China were included for the studies. Data was collected between April 2012 and January 2013 on SHS exposure and ADHD symptoms via questionnaire administered to parents or guardians by school teachers. Whereas, data was analyzed from September 14 to December 2, 2020.

Research results found

The analysis of the study data revealed that among 45562 participants, 2170 had ADHD symptoms. Children who were ever exposed or always exposed to SHS from pregnancy to childhood were more likely to develop ADHD symptoms and subtypes when compared with their unexposed counter parts.

Children with SHS exposure were more likely of having ADHD symptoms when exposed in the pre-natal period, early post-natal period, or current period when compared with their unexposed counterparts. Furthermore, children whose fathers smoked 10 or more cigarettes/d on both weekdays and weekends were more likely of having ADHD symptoms and subtypes when compared with their unexposed counterparts.

What we know now

Thus, the studies enabled the research team to conclude that SHS exposure from pregnancy to childhood was associated with ADHD symptoms and sub-types in school-aged children; and associations were somewhat stronger for SHS exposure during prenatal and early postnatal periods.

Moreover, the findings of the studies highlight the important public health implication of reducing SHS exposure which may decrease the health and economic burdens of individuals with ADHD.


Association of Prenatal, Early Postnatal, or Current Exposure to Secondhand Smoke with Attention-Deficit/Hyperactivity Disorder Symptoms in Children

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