| Summary: | 碩士 === 國防醫學院 === 公共衛生學研究所 === 96 === Folate is an essential nutrients in humans and plays an important role in one-carbon reactions that involve in DNA synthesis and DNA methylation reactions. Therefore, assessing the relationships of nutritional status of folate and cofactors which involve in folate metabolism with the risk of cancer is a critical subject for the etiology of cancer. Thus, we conducted this study to assess the relationships of dietary intake and plasma levels of folate, vitamins B6 and B12 within the overall risk of developing cancers. We also evaluated the differential effect of folate on the occurrence of cancer and the progression of precancerous lesions based on the analysis of prevalent cases(occurred with two years from the enrollment date) and incident cases(occurred after two years from the enrollment date). We further examined whether nutritional status of the vitamins B6 and B12 modified the association of folate status with cancer risk. This cohort study used two databases, including Nutrition and Health Survey in Taiwan, 1993-1996(included 949 participants) and CardioVascular Disease risk FACtor Two-township Study (included 4572 participants). Food questionnaire and blood samples were collected from each participant. Subjects were followed up from cohort entry to December 31, 2005, for vital status and cancer occurrence through computerized linkage with information obtained from the National Cancer Registry and the National Death Certification System in Taiwan. Cox proportional hazards model was used to estimate relative risks (RRs) and 95% confidence intervals (CIs). The results showed that the correlation between dietary folate, vitamins B6 and B12 intakes and their plasma levels were 0.20(p<0.05), 0.11(p=0.02), and 0.21(p<0.05), respectively. Dietary folate intake and plasma levels of folate were inversely associated with overall cancer risk (adjusted RR=1.2; 95% CI=0.85-1.59 and 0.88-1.54, respectively). For the analysis of prevalent cases, participants in the second tertile and the lowest tertile group showed an adjusted RR of 1.5(95% CI=0.36-3.38) and 0.2 (95%CI = 0.03 -0.72), respectively, as compared with those in the highest tertile. At the meantime, the analysis of incident cases showed that dietary folate intake was inversely associated with overall cancer risk (adjusted RR=1.2, 95% CI=0.86-1.66 and RR=1.1, 95% CI=0.84-1.51, respectively). Furthermore, the results demonstrated that the nutritional status of vitamins B6 and B12 was not modified the association of folate status with cancer risk. Further epidemiological cohort studies based on large sample size and prolonged duration of follow-up are needed to evaluate the potential dual modulator role of folate in carcinogenesis.
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