Dietary vitamin A and the risk of intraepithelial and invasive cervical neoplasia

The risk of invasive and intraepithelial cervical neoplasia in relation to the frequency of intake of the major sources of preformed vitamin A (retinol) and beta-carotene in the Italian diet was analyzed in a study of 392 cases of invasive cancer compared with 392 age-matched controls hospitalized for acute conditions unrelated to any of the established or suspected risk factors for cervical cancer, and of 247 cases of cervical intraepithelial neoplasia compared with 247 controls found to have normal smears at the same screening clinics where cases had been identified. Women with invasive cancer consumed milk, green vegetables, and carrots less frequently, but no significant relation was noted for meat or liver. Consequently, estimated beta-carotene, but not retinol, intake was inversely and strongly related to the risk of invasive cervical cancer. Compared with women whose intake was over 150,000 international units (IU) per month, the relative risks were 3.0 for 100 to 149,999 and 4.7 for less than 100,000 IU. It was not possible to show that these relationships were incidental, since allowance for several identified potential distorting factors, including indicators of social status and the major risk factors for cervical cancer, did not materially modify the risk estimates. In contrast, no association emerged between any of the food items and vitamin A estimates considered and intraepithelial neoplasia. Thus, the results of this study can be interpreted in one of two ways: either some residual uncontrolled bias was responsible for the strong dietary correlates of invasive cervical cancer risk or beta-carotene (or any other correlate of a vegetable-rich diet) has effect on one of the later stages of the process of carcinogenesis, thus influencing the risk of invasive carcinoma but not of its precursors.