Exposure to passive smoking in childhood as a risk factor for poorer health and wellbeing across the life course

Background: Exposure to passive smoking in childhood, which mainly comes from parents, continues to be a concerning major public health issue many years after comprehensive global action on tobacco control was initiated. This thesis aimed to examine (1) the prevalence, determinants and the trend of maternal smoking during pregnancy; (2) hospital use among children associated with exposure to maternal smoking during pregnancy; (3) validity and reliability of a life course questionnaire on exposure to passive smoking during childhood and (4) the effect of exposure to passive smoke across childhood on cardiovascular function in adulthood. Previous studies in these areas had limitations related to measurement of exposure or outcomes, were cross-sectional, or did not have objectively measured outcomes. This thesis sought to overcome these limitations, adding new information in these areas that could be important for public health policy and practice. Methods: Participants were drawn from three datasets, Tasmanian Conception to Community study (C2C), Childhood Determinants of Adult Health Study (CDAH) and Tasmanian Infant Health Study (THIS). C2C is a de-identified linked dataset comprising perinatal, emergency department, and admitted patient databases collected between the period July 2008 to June 2014. Data on maternal smoking during pregnancy and other study factors were self-reported by mothers and collected by midwives as part of nationally mandated perinatal datasets. Emergency department presentations and admission into hospital through ED were from public emergency department data. The CDAH study comprised of the 1985 Australian Schools Health and Fitness Survey (ASHFS) cohort aged 7- 15 years that were subsequently followed up in CDAH-1 (2004-06), CDAH-2 (2009-11) and CDAH-3 (2014 - 19). A range of validated measures of cardiovascular structure and function were assessed by trained data collectors at face-to-face clinics around Australia. Data on passive smoking during childhood was collected with questionnaires in childhood and adulthood. The TIHS included birth cohort between January 1988 to March 1990 that was followed up in 2015-16 for a pilot study of adult cardiovascular health. Measures of cardiovascular structure and function were taken in face-to-face clinics. Exposure to passive smoking during pregnancy and childhood was self-reported by mothers prospectively around the time of birth and shortly after. Results: The first study examined the trends and determinants of maternal smoking during pregnancy, changes in maternal smoking during pregnancy between and within pregnancies and their determinants in Tasmania, Australia. Maternal smoking during pregnancy declined from 25.9% (2008) to 16.4% (2014). A cessation proportion of 35.1% was observed between index (first birth recorded in the dataset) and last pregnancy. Maternal alcohol consumption during pregnancy, living in a highly socioeconomically disadvantaged area or being an Aboriginal or Torres Strait Islander was associated with an increase in the prevalence of maternal smoking during pregnancy and continued smoking between pregnancies. The second study evaluated the effect of exposure to passive smoking during pregnancy on ED presentations and admission into hospital through ED in exposed children up to 1-year and 5- years of age. Exposed children had 26% and 45% higher overall presentation to ED and admission into hospital through ED, respectively, compared to unexposed children at 5 years of age. Higher presentation and admission for respiratory, eye, ear, nose, and throat illnesses, systemic and parasitic infections and psychosocial/other presentations were observed above the level of the negative control outcome of poisoning or injuries in exposed children at 5 years. Similar results were obtained at 1 year. These effects had a dose-response relationship with increased rates of presentation and admission associated with higher exposure to cigarettes per day. The third study examined the reliability and validity of a retrospective questionnaire administered to middle-aged adults in CDAH phase 3 on prolonged exposure to tobacco smoke across childhood. The three measures of passive smoking derived from questions on other people smoking in the home (example. parents and siblings) included total household smoker (range: 0 to 5 smokers); cumulative years of exposure (range: 0 to 106 years) and severity of exposure index (range: 0 to 318). The three retrospective measures had good internal consistency and moderate agreement with childhood and adulthood factors in ASHFS and CDAH. The three measures were also significantly positively correlated with participant smoking and negatively with their lung function test. These results suggest that these measures are reliable and valid to measure prolonged passive smoke exposure from childhood to adulthood. The fourth study illustrated the effect of exposure to passive smoking across childhood using the previously validated measures on cardiovascular function in adulthood. Greater exposure to passive smoking across childhood from the total number of smokers in the household was associated with an increase in central blood pressure. Worse left ventricular function as measured by global longitudinal strain was associated with greater cumulative years of exposure to passive smoke. The fifth pilot study evaluated the effect of exposure to passive smoking during pregnancy and childhood on cardiovascular function in adulthood. There were significant increases in peripheral diastolic blood pressure and decreases in left ventricular function in children exposed to passive smoke at various time-points of exposure from pregnancy to adulthood. Conclusion: The findings in this thesis suggest that exposure to passive smoking during pregnancy and childhood negatively impacts the health of offspring in childhood and into adulthood. Though exposure to maternal smoking during pregnancy is declining, more work needs to be done to reduce exposure and improve the cardiovascular health of children exposed to this risk factor early in life.