The Association Between Second-hand Tobacco Smoke Exposure and Children’s Cardiorespiratory Fitness, Physical Activity, Respiratory Health, and Attitudes Towards Exercise

Cardiorespiratory fitness (CRF) is associated with a plethora of positive health effects in both adults and children, including reduced risk of cardiovascular disease, improved body composition, and a reduction in all-cause mortality. Physical activity (PA) is a major determinant of CRF and is also associated with a range of health-related quality of life markers. Many UK children fail to meet the recommended level of PA, with an observed decline in CRF levels in children over recent decades. Childhood CRF and PA are associated with health outcomes in later life, and so research is needed to understand the factors that contribute to CRF and PA in children, to ensure children become healthy adults. The health effects of active smoking are well-known, with approximately 16% of total deaths in the UK attributed to smoking. The health effects of second-hand smoke (SHS) are also well-researched, with SHS responsible for 1.2 million deaths worldwide, and a significant proportion of the worldwide burden of disease. However, less is understood regarding the impact of SHS exposure on CRF, and there is a distinct gap in the literature concerning the effect of SHS exposure on CRF in children. In addition, little is known about the impact of household smoking and SHS on children’s attitudes, beliefs, and perceptions of PA, fitness, and exercise. Accordingly, the overarching aim of this thesis was to use a mixed-methods approach to, quantitatively and qualitatively, explore the association between SHS exposure and CRF, PA, and respiratory health in children, and children’s attitudes to PA, fitness, and exercise. The aim of Study 1 was to use quantitative methods to explore the association between SHS exposure (as measured by the number of cigarettes smoked per household per day), and CRF, PA, PA enjoyment, and respiratory markers in children. Children in years 5 and 6 from four Merseyside primary schools participated in the study (n=104), including 38 children from smoking households. The study utilised quantitative surveys to determine household smoking habits and children’s PA and PA enjoyment, and laboratory-based methods to assess children’s VO2peak, spirometry, exhaled gases (carbon monoxide and nitric oxide), and anthropometrics. Linear regression was used to predict absolute (mL·min-1) and allometrically scaled (mL·kg-0.53·min-1) VO2peak from SHS exposure, adjusting for sex, age, mass (absolute VO2peak only), stature, maturation, PA, and deprivation. SHS exposure was found to be negatively associated with allometrically scaled VO2peak (B = -3.8, p = 0.030) but not absolute VO2peak (B = 17.4, p = 0.091), although both the absolute and allometrically scaled VO2peak regression models were statistically significant (p < 0.001) and explained 70.0% and 29.9% of the variance, respectively. Linear regression showed SHS exposure not to be a statistically significant predictor of PA, PA enjoyment, or respiratory measures in either the adjusted or unadjusted models. Results indicate that SHS exposure is associated with reduced CRF, but not PA, PA enjoyment or respiratory measures in children. This is the first study to examine the association between SHS and children’s CRF using direct measurement of VO2peak. Study 2 utilised creative focus groups with a sub-cohort of the larger sample (n=38), including 16 children from smoking households. The study aimed to explore children’s reasons for being physically active, children’s attitudes towards PA, fitness, and exercise, the perceived barriers and facilitators to PA, and children’s self-perceptions of fitness and physical ability, and how these differ for children from smoking and non-smoking households. The findings support the main hypothesised mediators of PA in children including self-efficacy, enjoyment, perceived benefit, and social support. Less than a quarter of children were aware of the PA guidelines, and whilst all children agreed fitness was important to them, there were differences in children’s reasons for why fitness was important. For example, children from non-smoking households believed fitness was important for health and performance, whereas children from smoking households were concerned with the negative physiological consequences of being unfit, such as ‘getting out of breath’. Variances emerged between important barriers (sedentary behaviours including screen time, psychological factors, the environment) and facilitators (opportunities for PA, significant others, psychological factors) for children from smoking and non-smoking households. The majority of children perceived their own fitness to be high, but children from smoking households rated running as more difficult than children from non-smoking households. This study is unique in the sense that it provides a voice to children from smoking households, and is also the first to explore and compare the perceptions of PA and fitness for children from non-smoking and smoking households. A series of case studies were used to draw together the complementary data from Study 1 and Study 2 using a mixed-methods case study approach. Cases were purposively selected based on sex, household smoking habits, child CRF, and PA data, to reflect the varied and contrasting circumstances of the participating children and their families. The case studies shed light on the individual differences and heterogeneity of the sample, as well as highlighting extreme examples, and cases that contradict the general trend. Exploration of the six unique cases has identified behaviours, perceptions, and circumstances that may be contributing to the individual’s health outcomes including CRF, respiratory health, and health-promoting behaviour such as PA participation and enjoyment. This thesis makes an original contribution to the body of research concerning children’s health, fitness, and PA, in relation to household smoking and SHS exposure. The studies included have provided an original and unique insight into the physical and psychological impacts of household tobacco smoking on children. Further research is now needed to explore in-depth, the behaviours, exposures, psychological factors, and possible mechanisms that contribute to the findings in this research.