Association of dietary intakes with risk of colorectal cancer : results from a population-based case-control study in Newfoundland and Labrador and Ontario

Sun, Zhuoyu (2010) Association of dietary intakes with risk of colorectal cancer : results from a population-based case-control study in Newfoundland and Labrador and Ontario. Masters thesis, Memorial University of Newfoundland.

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Abstract

Colorectal cancer (CRC) is the second leading cause of death from cancer in men and women combined in Canada. Research to date suggests that CRC is a result of complex genetic-environmental interactions and diet has long been regarded as the most important environmental factor. Yet epidemiologic studies have been inconclusive in demonstrating the role of dietary factors in the etiology of CRC. This thesis examined the effects of dietary factors on CRC risk using data from a large population-based case-control study conducted in Newfoundland and Labrador (NL) and Ontario (ON) through three coherent papers. The first two papers were based on pooled data from the two provinces assessing the effects of total energy/macronutrients and selected micronutrients on CRC, respectively. Overall, findings from these two parts of the thesis suggested that diets high in energy increased the risk, whereas diets high in fibre, carbohydrate and protein reduced the risk of CRC. Significant protective effects on CRC were also observed for calcium, vitamin D, vitamin C, riboflavin and folate. Stratified analyses by supplement intake status further indicated that the protective effects varied according to nutrients intake levels from foods. In addition, among individual supplement users, the protective effects were more pronounced in people with lower nutrients intake from foods. Based on the findings from the first two papers, this thesis further compared the effects of calcium, vitamin D and dairy products on the occurrence of CRC risk between two provinces. While the results were consistent in both provinces, statistical associations were only observed in the ON population. Additionally, this study also found significant synergistic effects between calcium and vitamin D intake. In summary, based on a large population case-control study, this thesis comprehensively evaluates various micronutrients and macronutrients in relation to CRC. This work corroborates and adds to the existing literature in many aspects. Findings from this thesis may have important public health implications, particularly for those with lower intakes for a number of selected nutrients, who can benefit greatly from supplement intakes.

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