Researchers from across Canada evaluated the impact of tobacco smoke exposure on infants during pregnancy and in the first three months after birth. Despite low rates of smoking, findings suggested nearly 25% of infants were regularly exposed to tobacco smoke, and the overwhelming majority had some exposure. 

May 25, 2022

Avery Crosley

A recent study by Jaclyn Parks from Simon Fraser University, British Columbia, led a team of colleagues from across Canada to assess second- and thirdhand tobacco smoke exposure in Canadian infants. Their goal was to better understand biomarkers of tobacco smoke exposure in populations with no reported exposure. While smoking rates have decreased in Canada, the research explored the pervasiveness of both second- and thirdhand smoke in infant populations.  

Cotinine and 3HC are two biomarkers of exposure to tobacco smoke. They are the unique chemical fingerprints that tobacco smoke leaves behind in a smoker or a nonsmoker exposed to secondhand and thirdhand smoke. Biomarkers provide the biological proof that someone was exposed to tobacco smoke chemicals. For instance, when nicotine is processed through a person, it is transformed into cotinine and 3HC, which circulate in the blood and are excreted in urine.

The study used data from the population-based CHILD Cohort Study that involved 3,455 mother-child pairs across Canada. The researchers followed up with the child-mother pairs over three months, conducted in-home visits, administered questionnaires, and collected infant urine samples to measure cotinine and 3HC levels. Data from the questionnaires helped the researchers characterize the source of tobacco smoke exposure which they then combined with biomarker results. There were three types of ways the researcher’s characterized exposure: (1) mother’s report of her exposure during pregnancy, (2) mother’s report of the child’s exposure at three months after birth, and (3) the research assistant’s evaluation of tobacco exposure at the three-month after birth home visit when the urine samples were collected from the infants. The questionnaires and the amount of cotinine and 3HC in the infant’s urine were assessed using machine learning to classify exposure type. The biomarkers helped verify the exposure level and exposure type when compared to results from the questionnaires.

Despite only 2% of mothers reporting smoking before or during pregnancy, cotinine was detected in the urine of 76% of the infants, and 3HC was detected in 89% of infants. The computer models suggested that infants of mothers who smoked during pregnancy had five times greater cotinine levels than infants of mothers who never smoked at all.

Socioeconomic factors influencing tobacco smoke exposure were evaluated too. The study found that children who lived with parents of lower education, lower household income, younger age, and in rental housing had higher tobacco smoke exposure. Children living in rented homes had, on average, a 23% higher concentration of urinary cotinine and 3HC compared to those who owned their homes. Children living in rental housing are at particular risk of exposure to thirdhand smoke, as reservoirs of toxic chemicals can remain for months and even years after the person who smoked has moved out.

Parents’ efforts to protect children by smoking outside do not appear to be effective. Although many parents changed their smoking location to outside the home during and after pregnancy, smoking outdoors does not protect children from thirdhand smoke—the harmful chemical residue that accumulates on surfaces after a cigarette is smoked. The study found that infants in a home with only outdoor smoking had cotinine levels three times greater than infants in homes with no reported smoking.

This research highlights that infants can be exposed to tobacco smoke pollutants without their parents noticing and even if their parents never smoked or no longer smoke. The findings suggest that although smoking rates have decreased, the dangers of thirdhand smoke and nicotine exposure are still widely seen across Canada. The authors suggest that other similar studies should be done around the world to better understand the exposure levels for nicotine compounds in people. 

Click here to read the research study.