Department of Public Health Sciences Graduate Theses

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    Development of a Canadian Index of Playability
    Boyes, Randall; Public Health Sciences; Janssen, Ian; Pickett, William
    This thesis describes the creation and testing of a Canadian index of the “playability” of neighbourhoods, defined as the degree to which neighbourhoods encourage unsupervised outdoor active play in children between the ages of 10 and 13. It consists of three manuscripts. The first manuscript describes the creation and testing of a novel measurement method for features of the built environment that have been associated with the propensity of children to engage in outdoor active play. Google Street View images were systematically downloaded from the area surrounding children’s homes and processed with a neural network to extract features of the built environment. The effectiveness of this method was measured against ground truth information. The second manuscript describes the initial development of a prediction model for time spent in unsupervised outdoor activity using a sample of children from three neighbourhoods in the Greater Vancouver Area. Predictor selection was based on qualitative interviews with children conducted by the Playability Project team at the University of British Columbia. A Bayesian model of play was constructed using prior probabilities informed by the things that children indicated were important for their engagement in play. The third manuscript tests and extends the model developed in manuscript two in a cross-Canadian population of children identified using the Health Behaviour in School-aged Children survey. The predictive validity of the initial model is compared against similar models trained in the HBSC data. The Playability score developed across these manuscripts shows a low correlation with play behaviour when tested outside of the training sample, but suggests avenues for future research into built environment predictors of the play behaviour of children. The score could be refined with larger-scale datasets with objective measurements of play, and future research could examine of the causal impact of these predictors using interventional trials or by taking advantage of natural experiments. An accurate index of Playability could be used to inform the development of neighbourhoods and cities that encourage outdoor active play in children, improving their health and well-being.
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    Patterns of solar ultraviolet radiation exposures and melanoma risk in Canada
    Waddingham, Claudia M.; Public Health Sciences; King, Will
    Solar ultraviolet radiation (UVR) exposure is established as the primary cause of cutaneous melanoma. It has been hypothesized that moderate time in the sun and intermittent sun exposure increases the risk of melanoma, while chronic sun exposure has no association or may even decrease the risk of melanoma. The aim of this thesis is to examine the relationship between average time in the sun, sun exposure patterns, residential ambient UVR, and occupational UVR exposure and melanoma risk in Canada. A prospective cohort study, the Canadian Partnership for Tomorrow’s Health, collected self-reported questionnaire data on sun exposure, occupational history, and other melanoma risk factors for three provincial cohorts (Alberta, Ontario, and Quebec). Individuals from the cohorts were linked to cancer registries or administrative datasets to identify melanoma cases. Average time in the sun and residential ambient UVR exposures were investigated using a cohort methodology, while a case-cohort design was utilized to assess occupational solar exposure and risk of melanoma. For assessing occupational solar exposure, an individual’s longest job held was coded to a solar job exposure matrix to assign solar exposure status. Multivariable Cox proportional hazard models with age as the time scale and adjusted for potential confounders were used to estimate hazard ratios for each investigated relationship. Neither average daily time in thesun, intermittent and chronic solar exposure patterns, nor ambient UVR were found to have a statistically significant relationship with melanoma risk. Additionally, occupational solar exposure was not associated with risk of melanoma (HRadj = 0.94; 95% CI = 0.63-1.41). Although this study found typical time in the sun was only suggestive of increasing melanoma risk and occupational solar exposure was not associated with melanoma risk, the results align with existing literature. Understanding how different patterns of solar UVR exposure affect the risk of melanoma among Canadians can help inform on strategies aimed at targeting modifiable solar behaviors to reduce the burden of melanoma.
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    An exploration of the associations between immigration status, racialized status and depressive symptoms: An epidemiological study guided by Intersectionality Theory
    Blaskevitch, Manisha; Public Health Sciences; Davison, Colleen; McIsaac, Michael
    Background: Disparities in adolescents' mental health in Canada stem from many environmental, genetic and social factors. Intersectionality Theory explains how people exist at the intersection of a combination of social identities including a person’s racial group, immigrant status, socioeconomic status (SES), and gender. Depressive symptoms can vary across such social identity factors, prompting exploration of their synergistic effects. This study delves into how the intersection of immigrant identity and race influences depressive symptom risk among Canadian adolescents. Objectives: 1) Describe the prevalence and risk profiles of depressive symptoms across various social identity factors. 2) Explore if the joint effect of immigration and race on depressive symptoms exceeds the risk of the sum of the two main effects produced by these variables independently. Methods: Data from the 2017/2018 Health Behaviour in School-aged Children survey involving Canadian grades 6-10 were used (n=20,108). Objective 1 assessed depressive symptom patterns for various social identity factors using proportions and estimates of relative risk. Objective 2 employed adjusted log-binomial regression to measure the interaction between immigration and race; relative risk estimates, relative excess risk due to interaction, synergy index, and attributable proportion were also obtained. Results: The interaction of race and immigration yields a unique protection. Racialized immigrant youth exhibit significantly lower depressive symptom risk (RR=0.81, 95% CI 0.73, 0.98) than non-immigrant, non-racialized peers. Among the racialized subgroup, immigration associates with substantial risk reduction of depressive symptoms (RR=0.64, 95% CI 0.50, 0.77). Among immigrant youth, racialized individuals show a non-significant risk difference when compared to their non-racialized counterparts (RR=0.76, 95% CI 0.10, 1.42). The interaction between racialized and immigrant identity produced a significant risk reduction of depressive symptoms beyond additivity. The relative excess risk due to interaction (RERI) was -0.52 (95% CI -0.73, -0.30). Conclusions: The findings highlight a protective synergy of these two factors, indicating substantial risk reduction beyond the individual influences. These insights emphasize the need for further exploration of synergistic effects and the use of Intersectionality Theory when assessing health risks for youth. Tailored interventions and support strategies, which consider the intersectionality of multiple social identities to enhance adolescent mental well-being, are indicated.
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    Ambient Polycyclic Aromatic Hydrocarbon Exposure and Breast Cancer Risk in a Population-Based Canadian Case-Control Study
    Hinton, Patrick; Public Health Sciences; King, Will; Villeneuve, Paul
    Background: Polycyclic aromatic hydrocarbons (PAHs) represent a class of ubiquitous pollutants which are emitted through combustion of organic materials and are recognized as established human carcinogens and endocrine-disrupting chemicals. There is a lack of epidemiological research investigating ambient PAH exposures and breast cancer risk. Additionally, PAHs have seldom been modelled at the population-level for epidemiological application, and current methods for assessment of long-term exposure are limited. This thesis evaluated associations between long-term residential exposure to ambient PAHs and breast cancer risk, both pre- and post-menopausal, in the Canadian setting. Methods: Using the National Enhanced Cancer Surveillance System (NECSS), a population-based case-control study conducted within eight of the Canadian provinces between 1994-1997, annual fluoranthene exposures were estimated using the GEM-MACH-PAH chemical transport model on the basis of geocoded residential histories throughout a 20-year exposure window. Odds ratios (ORs) and 95% confidence intervals (CIs) controlling for potential confounders were estimated using unconditional logistic regression. Separate analyses were conducted for Ontario and national samples given a finer-resolution exposure surface available for Ontario, as well as additional risk factor information collected in Ontario. Results: Positive associations were observed between long-term fluoranthene exposure and premenopausal breast cancer, with inconsistent findings for postmenopausal breast cancer. For premenopausal breast cancer, adjusted ORs of 2.48 (95% CI: 1.29, 4.77) and 1.59 (95% CI: 1.11, 2.29) were observed when comparing the second highest category of exposure to the lowest, amongst the Ontario and national samples, respectively. For postmenopausal breast cancer, adjusted ORs were 1.10 (95% CI: 0.67, 1.80) and 1.33 (95% CI: 1.02, 1.73). Associations for the highest level of exposure, across both samples and menopausal strata, were non-significant. Results were robust in sensitivity analysis restricted to those with more complete residence history, confounders controlled for, and simultaneous modelling of criteria air pollutant measures. Conclusion: This study provides support for the hypothesis that ambient PAH exposures are associated with an increase in risk for breast cancer, especially for premenopausal women.
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    Maternal Exposure to Metals and Time-to-Pregnancy: Results From the Maternal-Infant Research on Environmental Chemicals (MIREC) Pregnancy Cohort
    Premranjith, Priya; Public Health Sciences; Velez, Maria; King, Will
    Introduction: Environmental exposure to metals is a public health concern given their ubiquitous nature in the environment. Many of these metals are suggested to be endocrine-disrupting chemicals and have demonstrated adverse effects on women’s reproductive health, including irregular menstrual cycles, endometriosis, and infertility. However, there is weak evidence exploring the relationship between metals and fecundity, as measured by time-to-pregnancy (TTP), with previous studies showing inconsistent results. This thesis evaluates the association between metals (arsenic, cadmium, lead, manganese and mercury), TTP, and infertility in female participants from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. Methods: Chemical concentrations were measured in maternal blood during the first trimester of pregnancy. TTP in months was ascertained retrospectively, via self-report. Cox proportional hazards models modified for discrete-time data were used to calculate fecundability odds ratios (FORs) and 95% confidence intervals (CI) for the association between metal concentrations and TTP. Logistic regression generated odds ratios (ORs) for the association between metals and infertility. Models were adjusted for maternal age, pre-pregnancy BMI, education, income, recruitment site, and plasma lipids. Results: Exposure to arsenic, cadmium, manganese, or mercury was not associated with TTP or infertility. Increments of one standard deviation of lead concentrations resulted in a shorter TTP (adjusted FOR 1.08, 95% CI 1.01 – 1.16); however, the association was not linear when exposure was modeled in tertiles. For manganese, relative to the first tertile, the third tertile was associated with a decreased odds of infertility (adjusted OR 0.65; 95% CI 0.43 – 0.97); however this association was not observed for TTP. Conclusion: Results support that at current environmental levels of exposure, metals are not associated with decreased fecundability or infertility. This research adds to the limited body of literature examining the relationship between metals and TTP. Future research should investigate the role of lead on TTP and infertility.