Howe G R, Benito E, Castelleto R, Cornée J, Estève J, Gallagher R P, Iscovich J M, Deng-ao J, Kaaks R, Kune G A
NCIC Epidemiology Unit, University of Toronto, ON, Canada.
J Natl Cancer Inst. 1992 Dec 16;84(24):1887-96. doi: 10.1093/jnci/84.24.1887.
Colorectal cancer is a major public health problem in both North America and western Europe, and incidence and mortality rates are rapidly increasing in many previously low-risk countries. It has been hypothesized that increased intakes of fiber, vitamin C, and beta carotene could decrease the risk of colorectal cancer.
The objective of this study was to examine the effects of fiber, vitamin C, and beta-carotene intakes on colorectal cancer risk in a combined analysis of data from 13 case-control studies previously conducted in populations with differing colorectal cancer rates and dietary practices. The study was designed to estimate risks in the pooled data, to test the consistency of the associations across the studies, and to examine interactions of the effects of the nutrients with cancer site, sex, and age.
Original data records for 5287 case subjects with colorectal cancer and 10,470 control subjects without disease were combined. Logistic regression analysis was used to estimate relative risks and confidence intervals for intakes of fiber, vitamin C, and beta carotene, with the effects of study, sex, and age group being adjusted by stratification.
Risk decreased as fiber intake increased; relative risks were 0.79, 0.69, 0.63, and 0.53 for the four highest quintiles of intake compared with the lowest quintile (trend, P < .0001). The inverse association with fiber is seen in 12 of the 13 studies and is similar in magnitude for left- and right-sided colon and rectal cancers, for men and for women, and for different age groups. In contrast, after adjustment for fiber intake, only weak inverse associations are seen for the intakes of vitamin C and beta carotene.
This analysis provides substantive evidence that intake of fiber-rich foods is inversely related to risk of cancers of both the colon and rectum.
If causality is assumed, we estimate that risk of colorectal cancer in the U.S. population could be reduced about 31% (50,000 cases annually) by an average increase in fiber intake from food sources of about 13 g/d, corresponding to an average increase of about 70%.
结直肠癌在北美和西欧都是一个重大的公共卫生问题，而且在许多以前低风险的国家，其发病率和死亡率正在迅速上升。据推测，增加膳食纤维、维生素C和β-胡萝卜素的摄入量可能会降低患结直肠癌的风险。
本研究的目的是通过对之前在结直肠癌发病率和饮食习惯不同的人群中进行的13项病例对照研究的数据进行综合分析，来检验膳食纤维、维生素C和β-胡萝卜素摄入量对结直肠癌风险的影响。该研究旨在估计汇总数据中的风险，检验各项研究中关联的一致性，并研究这些营养素的影响与癌症部位、性别和年龄之间的相互作用。
将5287例结直肠癌病例受试者和10470例无病对照受试者的原始数据记录进行合并。采用逻辑回归分析来估计膳食纤维、维生素C和β-胡萝卜素摄入量的相对风险和置信区间，通过分层调整研究、性别和年龄组的影响。
随着膳食纤维摄入量的增加，风险降低；与最低五分位数相比，摄入量最高的四个五分位数的相对风险分别为0.79、0.69、0.63和0.53（趋势，P <.0001）。在13项研究中的12项中都观察到了膳食纤维与风险的负相关，而且对于左、右半结肠癌和直肠癌、男性和女性以及不同年龄组，其关联程度相似。相比之下，在调整了膳食纤维摄入量后，维生素C和β-胡萝卜素的摄入量仅显示出微弱的负相关。
该分析提供了实质性证据，表明富含膳食纤维食物的摄入与结肠癌和直肠癌的风险呈负相关。
如果假设存在因果关系，我们估计，通过将食物来源的膳食纤维摄入量平均增加约13克/天（相当于平均增加约70%），美国人群患结直肠癌的风险可降低约31%（每年50000例）。
