High intake of fat and a low intake of foods rich in antioxidants and fibre are suggested to be associated with risk of colorectal adenomas. Inconsistency may, however, be due to dietary assessment problems or differences in the identification of cases and controls. We have compared 87 adenoma cases aged 50-76 years with 35 healthy controls and 35 'hospital' controls. All the controls were matched for sex and age (+/-5 years) and proven to be free of polyps. Current habitual diet was measured by a 5-day dietary record by weighing. Regarding the intakes of vegetable fat, protein, cholesterol, vitamin A, total vitamin D, edible fats, coffee and fish and fish products, the outcomes of the analysis depended upon the source of controls. However, an increased adenoma risk compared with either set of controls related to a low consumption of vegetables, cereals, iron, vitamin C and fibre and a high intake of total fat was found. This is suggestive of substantial differences, since bias due to abdominal symptoms, the dietary records or an inappropriate choice of controls, would have affected the estimations. The findings give further strength to the role of these dietary factors in the formation of precancerous lesions in the large intestine.
A prospective endoscopic screening examination of a randomized population sample of 200 men and 200 women, aged 50-59 years, enabled the differentiation between individuals with and without polyps in the rectum and sigmoid colon. Both number of years of smoking and percentage years of life with smoking were associated with the presence of adenomas and hyperplastic polyps, both for men and women. No relationship was found between these factors or the daily number of cigarettes and the degree of dysplasia or the size or multiplicity of polyps. Two years' follow-up examination showed a tendency to fewer new polyps among male ex-smokers compared with smokers; however, the difference was not quite significant. No significant difference was found when comparing smokers with never smokers. In the relatively smaller groups of women no significant difference with regard to number of polyps was found among smokers, ex-smokers, and never smokers. The results provide evidence for an association between smoking and colorectal neoplasia and may suggest an initiating effect of smoking on carcinogenesis in the colon and rectum.
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