They compared intake of dietary vitamins and beta-carotene in more than 400 adults without adenomas - benign tumours that are precursors to cancer of the colon or rectum - with 360 adenoma cases.
They adjusted for age, sex, BMI, and energy and alcohol intakes and smoking status.
Writing in this month's issue of the Journal of Nutrition (135:2468-2472), the scientists report that folate and vitamins C and B6 were inversely related to adenoma risk whereas vitamin D tended to be inversely associated with risk.
They also found a significant interaction between beta-carotene and smoking, confirming the results of previous studies looking at this nutrient's link to cancer risk.
In non-smokers however, beat-carotene was inversely associated with adenoma risk, especially that of colon adenomas whereas in past or current smokers, the carotenoid was associated with a nonsignificant increase in the risk of colon adenomas.
The effects of vitamins and beta-carotene on the risk of colorectal adenomas had not been fully investigated before.
The authors thus concluded: "Our findings support a protective effect of folate and vitamins C and B6 irrespective of smoking habits, and a protective effect of beta-carotene in non-smokers only."
Smokers should be cautious about taking high doses of beta-carotene, they added.