The Motherisk Program, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, M5G 1X8 Canada.
Cancer Epidemiol. 2011 Feb;35(1):2-10. doi: 10.1016/j.canep.2010.11.004. Epub 2010 Dec 21.
Folic acid fortification and supplementation to prevent neural tube defects has led to concerns regarding increased risk of colorectal cancer. The results of existing studies have been inconclusive. The purpose was to examine the relationship between level of folate intake and the incidence of colorectal cancer.
A systematic review and meta analysis were conducted. MEDLINE, Embase, and SCOPUS were searched from inception to October 2009 with the following search terms "folic acid," "folate", "colorectal cancer," "colon neoplasms," rectal neoplasms." Observational studies in adult populations were included that defined levels of folate intake and incidence of colorectal cancer.
Out of 6427 references, 27 studies met our inclusion criteria. The summary risk estimate for case control studies comparing high versus low total folate intake was 0.85 (CI 95% 0.74-0.99) with no significant heterogeneity among studies. Similarly, for cohort studies, the resulting summary risk estimate for high versus low dietary folate intake was 0.92 (CI 95% 0.81-1.05) with no significant heterogeneity. However, defining what represents a higher intake of folic acid is difficult as there is variability in the upper limit of folic acid intake used in the studies.
These results suggest that higher folate intake levels offer a reduction in one of the perceived risks associated with developing colorectal cancer. These data can serve to help reassure women planning a pregnancy to increase folic intake during the preconception period to levels sufficient to prevent neural tube defects.
叶酸强化和补充以预防神经管缺陷，这导致了人们对结直肠癌风险增加的担忧。现有研究的结果尚无定论。本研究旨在探讨叶酸摄入量与结直肠癌发病率之间的关系。
系统评价和荟萃分析。从建库到 2009 年 10 月，我们使用以下检索词在 MEDLINE、Embase 和 SCOPUS 中进行检索：“叶酸”、“叶酸”、“结直肠癌”、“结肠肿瘤”、“直肠肿瘤”。纳入了在成年人群中进行的观察性研究，这些研究定义了叶酸摄入量的水平和结直肠癌的发病率。
在 6427 篇参考文献中，有 27 篇符合我们的纳入标准。病例对照研究比较高与低总叶酸摄入量的汇总风险估计值为 0.85（95%CI 0.74-0.99），研究之间无显著异质性。同样，对于队列研究，高与低饮食叶酸摄入量的汇总风险估计值为 0.92（95%CI 0.81-1.05），研究之间无显著异质性。然而，很难确定什么代表叶酸的高摄入量，因为研究中使用的叶酸摄入量上限存在差异。
这些结果表明，较高的叶酸摄入量水平可降低与结直肠癌发生相关的一种公认风险。这些数据有助于使计划怀孕的妇女放心，在怀孕前增加叶酸摄入，使其达到足以预防神经管缺陷的水平。
