Physical activity, the direct and indirect effect of socioeconomic status on risk factors of colorectal cancer in Canada

Zhao, Jing (2012) Physical activity, the direct and indirect effect of socioeconomic status on risk factors of colorectal cancer in Canada. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (32MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The objective of this thesis was to examine the determinants of colorectal cancer(CRC) from two perspectives: 1) the associations between recreational physical activity and the risk of CRC; 2) the direct and indirect effect of socioeconomic status on the risk of CRC. -- Higher levels of physical activity have been consistently associated with lower risk of CRC in previous studies. Nevertheless, the specific mode, intensity, frequency, and duration of physical activity required for CRC prevention are not well known and remain controversial. The first objective of this study is to examine the associations of walking, non-walking exercise, and total recreational physical activity on colorectal cancer development. The study used the data collected from the existing population based case-control study of Ontario (ON) and Newfoundland and Labrador (NL), in which personal history, life style and dietary information were collected using the Personal History Questionnaire (PHQ), Food Frequency Questionnaire (FFQ) and Family History Questionnaire (FHQ). Multivariable logistic regression analysis was used to estimate odds ratios(OR) and 95% confidence interval (95%CI) after adjusting potential confounding covariates. Pooled analysis in both ON and NL was also conducted. Results from this study showed that the highest quintile of walking was associated with increased colorectal cancer risk for both males and females in both provinces (highest VS lowest: ON: OR=1.51, 95%CI=l.07-2.13; NL: OR=2.01,95%CI=1.25-3.22; pooled analysis: OR=1.70, 95%CI=1.09-2.66). However, this result could be biased because a higher proportion of cases responded to this item than controls. Non-walking exercise was insignificantly associated with a reduced risk of colorectal cancer for both sexes and provinces. These findings suggested that increasing amounts of neither walking nor non-walking exercise was associated with reducing the risk of colorectal cancer. More specified prospective studies on physical activity are needed to evaluate effective frequency, duration and intensity of physical activity in relation to colon and rectal cancer prevention. -- Existing epidemiologic studies have not investigated how risk factors work together to increase the incidence of CRC; therefore, the true effect of each factor could be under- or over-estimated. The second component of this thesis was to explore how socio-cconomic status(SES) directly influences the risk of developing CRC and its mediated effect on CRC risk through diet while adjusting for possible risk factors of alcohol intake, smoking, physical inactivity, and obesity. Using the data from just the NL province, measurement and structural modeling was used to test conceptual models. Exploratory factor analysis was used to identify dietary patterns measured by 39 food groups. Next, the direct and intermediate effects of risk factors were examined using structural equation modeling. The results from multivariable regression analysis indicated that age (OR=l.03), SES (OR=O.89), processed meat intake (OR=1.08), non-screening (OR=2.67), smoking (OR=1.44, 1.85 (ever, current)), and family history score of CRC(OR=l.06), were significantly associated with the risk of CRC. SES (β=0.05) has a direct effect on the risk of CRC and the indirect effect (β=0.06) of SES on the risk of CRC also appeared to exist through processed meat intake (β=0.01), lower vegetable intake (β=0.01), lower screening frequency (β=0.02), and smoking (β=O.02). This study indicated that the NL population has three major dietary patterns. Also, structural equation modeling used in this study, a relatively new approach in epidemiology studies, provided unique information of the direct effect of SES on the development of CRC and its indirect effects through a set of candidate CRC risk factors. -- KEYWORDS: Colorectal cancer; physical activity; socioeconomic status; diet pattern; direct effect; indirect effect.

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