A nested case‐control study of dietary factors and the risk of incident cytological abnormalities of the cervix

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Abstract
Several earlier case‐control studies reported inverse associations of cervical squamous intraepithelial lesions (SIL) with high dietary or biomarker levels of carotenoids, folate, and vitamins C and E. However, most studies did not measure the primary causal factor, cancer‐associated genital human papillomaviruses (HPV), now detected by sensitive viral DNA tests. This nested case‐control study assessed whether high dietary intakes of these nutrients, plus zinc and vitamin A, reduced SIL risk in cancer‐associated HPV DNA‐positive women. Using a 60‐item food‐frequency questionnaire, nutrient estimates were obtained for 33 incident cases with high‐grade lesions, 121 with low‐grade lesions, 97 with equivocal SIL, and 806 cytologically normal controls sampled from a large prospective cohort study. Baseline cervicovaginal lavages were tested for HPV DNA by the polymerase chain reaction. Among DNA‐positive cases (n = 68) and controls (n = 69), age‐adjusted odds ratios (ORs) of SIL in the highest vs. the lowest nutrient quartiles were 1.4 [95% confidence interval (CI) = 0.5–4.2] for vitamin A, 0.6 (CI = 0.2–2.0) for ß‐carotene, 1.3 (CI = 0.4–3.6) for vitamin C, 1.0 (CI = 0.4–3.6) for vitamin E, 0.7 (CI = 0.3–2.1) for folate, and 0.8 (CI = 0.3–2.2) for zinc. ORs in HPV DNA‐negative women approximated 1.0, with the exception of vitamin E (OR = 0.5, CI = 0.3–0.9). These results do not support a protective role for the above nutrients against low‐grade or equivocal SIL, which constituted the majority of diagnoses in this study.

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