Tea as a Potential Chemopreventive Agent in PhIP Carcinogenesis: Effects of Green Tea and Black Tea on PhIP-DNA Adduct Formation in Female F-344 Rats

Disturbances in DNA methylation have been hypothesized as being involved in carcinogenesis. It has been proposed that dietary factors such as folate, alcohol, and methionine may be associated with colon cancer because of their involvement in DNA methylation processes. Data from a large retrospective population‐based case‐control study of incident colon cancer were used to evaluate whether intake of alcohol and other dietary factors involved in DNA methylation are associated with colon cancer. Dietary data were obtained using a detailed diet history questionnaire. We did not observe strong independent associations between folate, vitamin B6, vitamin B12, methionine, or alcohol and risk of colon cancer after adjusting for body size, physical activity, cigarette smoking patterns, energy intake, and dietary intake of fiber and calcium. However, when assessing the associations between colon cancer and a composite dietary profile based on alcohol intake, methionine, folate, vitamin B12, and vitamin B6 we observed a trend of increasing risk as one moved from a low‐ to a high‐risk group. This trend was modest and most marked in those diagnosed at a younger age odds ratio (OR) for men = 1.3, 95% confidence interval (CI) = 0.9–1.9; OR for women = 1.6, 95% CI= 1.0–2.6]. We observed that associations with this high‐risk dietary profile were greater among those who took aspirin or nonsteroidal anti‐inflammatory drugs on a regular basis and were younger at the time of diagnosis (men OR = 1.7, 95% CI = 1.0–3.2; women OR = 2.2, 95% CI= 1.0–4.8) and for distal tumors (men OR = 1.4, 95% CI = 0.9–2.3; women OR = 2.0, 95% CI = 1.0–3.8). Findings from this study provide only limited support for previously reported associations between dietary factors involved in DNA methylation and risk of colon cancer.