Health Service Management Research Center, Tabriz University of Medical Sciences, Tabriz 51666114731, Iran; Department of Epidemiology, University Medical Center Groningen, University of Groningen, Groningen 9713 GZ, The Netherlands.
Hematology and Oncology Research Center, Tabriz University of Medical Sciences, Tabriz 51666114731, Iran.
Clin Nutr. 2018 Dec;37(6 Pt A):1926-1934. doi: 10.1016/j.clnu.2017.10.010. Epub 2017 Oct 28.
BACKGROUND & AIMS: To evaluate the controversies among the studies assessing the association between folic acid intake or folate status and colorectal cancer risk.
PubMed, Cochrane library and references of related articles were searched from January 2000 to September 2016. Studies on folic acid intake or folate status and colorectal cancer or adenoma risk were included. Full text review was conducted for potentially eligible studies. Quality assessment was performed. Random-effects meta-analysis was used to estimate risk ratio and 95% Confidence Intervals. Analysis was conducted by Comprehensive Meta-Analysis software.
Folic acid supplement intake showed no significant effect on colorectal cancer risk in meta-analysis of randomized controlled trials, RR: 1.07 (95% CI: 0.86-1.43). The effect on risk was not significant in cohort studies either; RR = 0.96 (95% CI: 0.76-1.21). However, there was significant reduced colorectal cancer risk in total folate intake in cohort studies; 0.71 (95% CI: 0.59-0.86). Odds Ratio was also significantly reduced in case control studies; 0.77 (95% CI: 0.62-0.95). Nevertheless once folate status was measured as Red Blood Cell folate content, no significant effect on colorectal cancer risk was observed; 1.05 (95% CI: 0.85-1.30).
The differences in bioavailability and metabolism of synthetic folic acid and natural dietary folate as well as variation in the baseline characteristics of subjects and various methods of folate status assessment might be the main reasons for these controversies. Findings of present study highlight the importance of individualized folic acid supplement intake given the fact that the beneficiary effects of long term folic acid supplementation is not confirmed.
评估评估叶酸摄入或叶酸状态与结直肠癌风险之间关联的研究中的争议。
检索 2000 年 1 月至 2016 年 9 月期间的 PubMed、Cochrane 图书馆和相关文章的参考文献。纳入关于叶酸摄入或叶酸状态与结直肠癌或腺瘤风险的研究。对潜在合格的研究进行全文审查。进行质量评估。使用随机效应荟萃分析来估计风险比和 95％置信区间。使用 Comprehensive Meta-Analysis 软件进行分析。
在随机对照试验的荟萃分析中，叶酸补充剂摄入对结直肠癌风险没有显著影响，RR：1.07（95％CI：0.86-1.43）。队列研究也没有观察到对风险的显著影响；RR=0.96（95％CI：0.76-1.21）。然而，在队列研究中，总叶酸摄入量与结直肠癌风险降低显著相关；0.71（95％CI：0.59-0.86）。病例对照研究中的比值比也显著降低；0.77（95％CI：0.62-0.95）。然而，一旦将叶酸状态测量为红细胞叶酸含量，就不会观察到对结直肠癌风险的显著影响；1.05（95％CI：0.85-1.30）。
合成叶酸和天然膳食叶酸的生物利用度和代谢差异以及研究对象的基线特征的变化以及各种叶酸状态评估方法的差异可能是这些争议的主要原因。本研究的结果强调了个体化叶酸补充摄入的重要性，因为长期补充叶酸的受益效果尚未得到证实。
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