Pediatric Sleep Apnoea and Passive Smoking: A Window of Opportunity?

The prevalence of obstructive sleep apnea (OSA) in children is between 1% and 4%, although this disorder is significantly underdiagnosed despite its serious repercussions.¹ OSA is characterized by recurrent episodes of partial or complete upper airway obstruction, associated with intermittent hypoxia and a proinflammatory state.² As a result, OSA can lead to cardiovascular, neurocognitive, and metabolic disturbances as well as delayed growth.³

Compared with adults, children are more susceptible to environmental pollutants owing to their smaller alveolar surface area, lack of collateral ventilation (pores of Kohn and canals of Lambert), greater peripheral airway resistance, less effective cough, and immature immune system.⁴ Prenatal exposure to tobacco smoke may be a risk factor for developing sleep-disordered breathing because nicotine can cross the placental barrier and induce placental insufficiency, fetal hypoxia due to increased carboxyhemoglobin concentrations, and alterations in brainstem regions associated with regulating wakefulness.⁵ All these mechanisms can impair arousability, one of the main protective mechanisms against sleep-disordered breathing in children.^5,6 Furthermore, both maternal smoking during pregnancy and passive smoking after birth have been associated with sudden infant death syndrome, with the risk increasing proportionally to the intensity of smoke exposure.⁷

The available evidence regarding passive smoking in children relates to secondhand smoke (as opposed to third- and fourth-hand smoke, discussed further down).^8–10 Secondhand smoke is a combination of sidestream smoke and exhaled mainstream smoke diluted with ambient air, and it contains over 7000 chemicals.⁸ Unlike mainstream smoke, sidestream smoke is a product of incomplete combustion; as such, it contains smaller particles and a larger quantity of waste products. In addition, some components (e.g. nicotine) can be transmitted as gases rather than particles and react with agents such as ozone, nitrous acid, and other oxidants, producing nitrosamines that increase cancer risk in non-smokers.⁹ Regarding the relationship between secondhand smoke and sleep-disordered breathing in the pediatric population, Subramanyam and colleagues found that among children with severe OSA, those exposed to secondhand smoke had a higher median apnea–hypopnea index (AHI) than those without this exposure (20.9 vs 19.5, p = 0.04). There was no significant association without stratification by severity. In a multivariable analysis, secondhand smoke exposure increased AHI by 48% (95% CI 8–102%, p = 0.01) in the severe OSA subgroup.¹⁰ Groner and colleagues reported an increased risk of sleep-disordered breathing in children aged two to five years exposed to secondhand smoke, with exposure determined by hair nicotine level.¹¹ In their meta-analysis of 26 studies, Chang and colleagues found that children exposed to secondhand smoke presented a higher risk of OSA (risk ratio [RR] 1.84) than adult passive smokers (RR 1.35).¹²

There are other, commonly overlooked forms of passive smoking that could increase the risk of sleep-disordered breathing. Thirdhand smoke refers to the residual chemicals from tobacco smoke (e.g. nitrosamines, toxic metals, alkaloids, organic combustion products, and volatile organic compounds) that adhere to indoor surfaces (e.g. curtains, rugs, furniture), dust particles, hair, clothing, vehicle upholstery, etc. They can persist for months after secondhand smoke has dissipated, leading to the continuous transfer of toxins.¹³ Children are particularly vulnerable to thirdhand smoke because they spend a considerable portion of the day at home. This situation was exacerbated during the COVID-19 lockdowns.

Fourth-hand smoke refers to environmental pollution and biodiversity changes (due to water pollution) caused by tobacco waste products. Cigarette butts are especially harmful, as they can take eight to 12 years to decompose and are made up of toxic substances such as pesticides, nicotine, diethylene glycol, tar, and ethylphenol.¹⁴ What is more, there have been many reported cases of accidental cigarette butt ingestion (e.g. in parks and at beaches) leading to neurological toxicity and vomiting in children.¹⁵ Despite the potential impact of third- and fourth-hand smoke, there are no pediatric studies evaluating the association of these exposures with sleep-disordered breathing.

Spain recently implemented its 2024–2027 comprehensive smoking prevention and control plan. While this represents a step in the right direction, there is still a need for legislative changes aimed at reducing secondhand tobacco exposure, limiting new forms of use, and protecting children. Public awareness and education campaigns targeted at specific risk groups such as Romani people, adolescents, or parents during pregnancy/after birth are also crucial for reducing exposure among children.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors’ contributions

All authors have contributed to the preparation, writing and review of the article.

Conflicts of interest

The authors declare not to have any conflicts of interest that may be considered to influence directly or indirectly the content of the manuscript.