RESUMEN
BACKGROUND & AIMS: Folate intake has been inversely associated with colorectal cancer risk in several prospective epidemiologic studies. However, no study fully assessed the influence of the high levels of folate that are frequently consumed in the United States as a result of mandatory folate fortification, which was fully implemented in 1998, and the recent increase in use of folate-containing supplements. There is evidence that consumption of high levels of folic acid, the form of folate used for fortification and in supplements, has different effects on biochemical pathways than natural folates and might promote carcinogenesis. METHODS: We investigated the association between folate intake and colorectal cancer among 43,512 men and 56,011 women in the Cancer Prevention Study II (CPS-II) Nutrition Cohort; 1023 were diagnosed with colorectal cancer between 1999 and 2007, a period entirely after folate fortification began. Cox proportional hazards regression was used to calculate multivariate hazards ratios (RR) and 95% confidence interval (CI). RESULTS: Intake of high levels of natural folate (RRQ5vsQ1=0.86; 95% CI: 0.70-1.06; P trend=.12) or folic acid (RRQ5vsQ1=0.84; 95% CI: 0.68-1.03; P trend=.06) were not significantly associated with risk of colorectal cancer. Total folate intake was significantly associated with lower risk (RRQ5vsQ1=0.81; 95% CI: 0.66-0.99; P trend=.047). CONCLUSIONS: Intake of high levels of total folate reduces risk of colorectal cancer; there is no evidence that dietary fortification or supplementation with this vitamin increases colorectal cancer risk.
Asunto(s)
Neoplasias Colorrectales/prevención & control , Suplementos Dietéticos , Ácido Fólico/administración & dosificación , Alimentos Fortificados , Anciano , Neoplasias Colorrectales/inducido químicamente , Neoplasias Colorrectales/epidemiología , Dieta , Suplementos Dietéticos/efectos adversos , Conducta Alimentaria , Femenino , Ácido Fólico/efectos adversos , Alimentos Fortificados/efectos adversos , Humanos , Incidencia , Masculino , Modelos de Riesgos Proporcionales , Estudios Prospectivos , Medición de Riesgo , Factores de Riesgo , Encuestas y Cuestionarios , Factores de Tiempo , Estados Unidos/epidemiologíaRESUMEN
BACKGROUND: Epidemiologic studies of the association of folate intake with breast cancer risk have been inconclusive, and few have investigated how related nutrients modify this association. OBJECTIVE: We investigated the association of dietary (food folate plus folic acid from fortification) and total folate (food folate, folic acid from fortification, and folic acid from supplements), vitamin B-6, vitamin B-12, methionine, and alcohol intakes with postmenopausal breast cancer among women in the Cancer Prevention Study II Nutrition Cohort. The modification of the folate associations by the other nutrients was also investigated. DESIGN: This prospective cohort study included 70,656 postmenopausal women for whom dietary information was collected in 1992. Of these, 3898 developed breast cancer between enrollment in 1992 and June 2005. Cox proportional hazards modeling was used to calculate multivariate-adjusted hazard rate ratios and 95% CIs. RESULTS: Compared with the lowest quintile, the highest quintile of dietary folate intake was associated with a higher risk of breast cancer (rate ratio: 1.12; 95% CI: 1.01, 1.24). However, the test for trend was not significant (P for trend = 0.15). No association was found for total folate, vitamin B-6, or vitamin B-12, but methionine was inversely associated with breast cancer risk (P for trend = 0.04). The association of dietary folate with breast cancer was not modified by other nutrients or alcohol. CONCLUSIONS: This study suggests that dietary folate intake may be positively associated with postmenopausal breast cancer. However, no dose-response relation was observed. The extent to which increased supplement use and folate fortification contributes to breast cancer risk warrants further research.