Food-group consumption and colon cancer in the Adelaide Case-Control Study. I. Vegetables and fruit.

Previous epidemiologic studies have shown an inverse association between vegetable and fruit consumption and risk of colon cancer. Vegetables and fruit contain a large number of potentially anti-carcinogenic substances, thus lending biological plausibility to this association. We conducted a case-control study in Australia, comparing 220 persons with histologically confirmed incident adenocarcinoma of the colon with 438 age- and gender-matched controls. Cases were identified via the South Australian Cancer Registry (1979-80); controls were randomly selected from the electoral roll. All participants completed a 141-item food-frequency questionnaire and were interviewed regarding demographic and other information. Consumption of 15 vegetable and fruit groups was investigated. Odds ratios (OR) for quartiles of consumption were derived using conditional logistic regression. All analyses were conducted separately for females and males. For females, greater intakes of onions and legumes were associated with decreased risk, with protein-adjusted OR of 0.48 and 0.53 respectively. Greater intakes of raw fruit and cabbage were associated with protein-adjusted OR of 0.76 and 0.71 respectively. For males, greater intakes of onions, green leafy vegetables, legumes, carrots and cabbage were associated with protein-adjusted OR in the range of 0.72 to 0.77. Consumption of potatoes was positively associated with risk in both genders. All 95% confidence intervals included 1.0. Analyses stratified by colon-cancer sub-site showed no strong and consistent differences between sub-sites for the vegetable and fruit associations. Results for meat, poultry, seafood, dairy foods and eggs are presented in a companion report.