Associations of Dietary Fats with Incident Colorectal Cancer in the Iowa Women’s Health Study Pubblico
Thuneibat, Muhammad (Spring 2019)
Abstract
The associations of dietary fats with incident colorectal cancer (CRC) across previous studies have been inconsistent. Certain types of dietary fats are proposed to increase CRC risk through pro-inflammatory mechanisms and stimulating the secretion of bile acids, while others are proposed to decrease risk. To address the inconsistency, we investigated associations of intakes of total fats, animal fats, vegetable fats, saturated fats, polyunsaturated fats, monounsaturated fats, and trans-fats with incident CRC in the prospective Iowa Women’s Health Study. Of the 35,221, 55-69-year-old women who were cancer-free at baseline in 1986, 1,731 developed incident CRC during follow-up through 2012. Diet was assessed using a Willett semi-quantitative food frequency questionnaire. Fat intakes were adjusted for energy intakes using the residual method. Fat intake residuals were categorized into quintiles, and associations estimated using multivariable Cox proportional hazards regression models. For those in the highest relative to the lowest total fat quintiles, the adjusted hazard ratios and 95% confidence intervals for overall, proximal, and distal CRC were 0.95 (0.77 – 1.10; Ptrend = 0.35), 0.86 (0.67 – 1.09; Ptrend = 0.22), and 1.06 (0.81 – 1.39; Ptrend = 0.92), respectively. The estimated associations of the various fat subtypes with CRC were similarly close to null. Our findings suggest that dietary fats may not be associated with risk for incident colorectal cancer among older Iowa women.
Table of Contents
CHAPTER I 1
LITERATURE REVIEW 1
BACKGROUND 2
RISK FACTORS 3
DIETARY FATS and SUBTYPES 3
BIOLOGICAL MECHANISMS 4
LITERATURE FINDINGS 5
STUDY PURPOSE 7
CHAPTER II 8
MANUSCRIPT 8
ABSTRACT 9
INTRODUCTION 10
MATERIALS AND METHODS 11
Study Population and Design 11
Dietary Assessment 12
Outcome Assessment 12
Statistical Analysis 13
RESULTS 16
DISCUSSION 17
TABLES 24
Table 1. Selected baseline characteristics of the participants according to quintiles of energy-adjusted total dietary fat in the Iowa Women’s Health Study (n = 35,221), 1986 – 2012 25
Table 2. Associations of total dietary fat and its subtypes with incident colorectal cancer among the Iowa Women’s Health Study participants (n = 35,221), 1986 – 2012 26
Table 3. Multivariable-adjusted associations of total dietary fat with incident colorectal cancer according to categories of selected participant characteristics; the Iowa Women’s Health Study (n = 35,221), 1986 - 2012 28
Table 4. Multivariable-adjusted associations of total and subtypes of dietary fat with incident proximal and distal colorectal cancers among Iowa Women’s Health Study participants (n = 35,221), 1986 – 2012 30
CHAPTER III 32
SUMMARY, PUBLIC HEALTH IMPLICATIONS, AND POSSIBLE FUTURE DIRECTIONS 32
REFERENCES 34
APPENDIX 42
Supplement Table 1. Associations of total dietary fat with incident colorectal cancer after excluding participants who died or were diagnosed with colorectal cancer within one, two, and six years of follow-up; the Iowa Women’s Health Study, 1986 – 2012 43
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