The Oxford Vegetarian Study (Appleby et al, 1999
) is a prospective investigation of 11
140 vegetarians and nonvegetarians who were recruited in the United Kingdom between 1980 and 1984. Participants were contacted through the Vegetarian Society of the United Kingdom, publicity in the national and local media, and word of mouth via participants already recruited. Non-vegetarian participants were recruited by the vegetarian participants, who were asked to nominate friends and relatives who ate meat, fish, or both.
Upon entry in to the study, participants completed a questionnaire including a simple food frequency questionnaire. Questions on other lifestyle factors related to health (smoking, alcohol consumption, and amount of exercise), date of birth, occupation, height and weight, and medical history (including illnesses related to the risk of cardiovascular disease and, for women, reproductive history) were also included. The validity of the questionnaire has been examined for estimating dietary fibre intake, but not for other nutrients (Gear et al, 1979
). Participants were categorised into tertiles of the distribution of intake of total fat from animal foods (meat, eggs, milk, and cheese), as well as for dietary fibre derived from cereals, fruit, and vegetables. Participants were classified as vegetarians (including lacto-ovo-vegetarians and vegans) or nonvegetarians (meat eaters and people who ate fish but not meat), using their answers to questions on the consumption of meat, fish, dairy products, and eggs.
Each participant was flagged at the UK National Health Service central register and participants were followed for information on cancer registration and death. Participants were included in this analysis if they were aged 16–89 years at entry, had not been diagnosed with a malignant cancer before recruitment (except for nonmelanoma skin cancer, ICD9 code 173), and could be classified according to their smoking status and alcohol consumption. Participants were followed up to 31 December 1999, subject to censoring at age 90.
Cox's proportional hazards model was used to estimate the association between selected nutritional and lifestyle factors and the risk of colorectal cancer. All incidence rate ratios were adjusted for age at recruitment (in 11 categories: <40, 40–44, 85–89 years) and sex. Further adjustments were made for smoking status (in three categories: never, former, and current smoker) and alcohol consumption (in three categories: non-/occasional drinker, 1–7
). The statistical analysis was performed using the STATA statistical package (StatCorp. 2001