| Summary: | Thesis (Ph.D.)--Memorial University of Newfoundland, 2010. Medicine Includes bibliographical references (leaves 194-232) Between 1999 and 2003, a large colorectal cancer (CRC) case-control study was conducted in Newfoundland and Labrador (NL). The primary aim of this thesis was to explore relations between use of alcohol and tobacco and CRC risk. The specific objectives were to (i) determine the extent of non-participation bias by comparing the differences in demographics between participants and non-participants; (ii) explore misreporting for tobacco and alcohol use using provincial sales data and the Canadian Community Health Survey (CCHS) 1.1 and 3.1 data for alcohol and tobacco; (iii) examine impact of tobacco smoking on risk of CRC; (iv) examine impact of alcohol consumption on risk of CRC. -- Newly diagnosed CRC cases identified in 1999-2003 in NL, Canada were frequency-matched by age and sex with controls selected using random digit dialing (RDD). Cases (n = 702) and controls (n = 717) completed self-administered questionnaires assessing health and lifestyle variables. Measures of tobacco use included type of tobacco, age of initiation of smoking, years of smoking, years since started smoking, number of cigarettes smoked daily, pack years, and years since abstention from smoking. Estimates of alcohol intake included types of beverage, years of drinking, and number of drinks daily. Odds ratios were estimated using multivariate logistic regression. The study found a 49% higher risk of CRC among cigarette smokers than non-smokers. The risk tended to increase significantly with cigarette smoking years, amount of cigarettes smoked daily, cigarette pack years and the risk significantly decreased with years of abstention from smoking. Smoking demonstrated a stronger cancer risk in men than women, in drinkers than non-drinkers and in obese men than obese women. The study demonstrated that the effect of alcohol intake on odds of developing CRC differed by weight status. Alcohol consumption tended to reduce the odds of developing CRC in non-obese. In the obese (BMI > 30), the odds of CRC (OR = 2.25) were greater in drinkers than in non-drinkers. The odds of developing CRC increased with number of drinking years and numbers of drinks daily in obese. The effect of drinking on CRC risk was stronger among obese subjects who smoked. -- In conclusion, this thesis reported that cigarette smoking increased the risk of CRC. Alcohol drinking decreased CRC risk in non-obese and cigarette non-smokers, but drinking increased the risk of CRC in the presence of cigarette smoking and obesity. Low participation rates may limit the generalizability of the results.
|
|---|