Department of Nutrition and Epidemiology, Harvard School of Public Health, Boston, Massachusetts.
Department of Nutrition and Epidemiology, Harvard School of Public Health, Boston, Massachusetts; Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
Am J Prev Med. 2014 Mar;46(3 Suppl 1):S65-72. doi: 10.1016/j.amepre.2013.10.025.
The U.S. has been reported as the only country experiencing a decline in incidence rates of colorectal cancer (CRC), despite increasing prevalence of CRC major risk factors, including the Western dietary pattern and obesity. This paper presents a hypothesis that improved folate status in the U.S. is the factor that could most likely explain the seemingly contradictory phenomenon, although a momentary increase in CRC incidence rates was observed in the later 1990s with the initiation of nationwide folic acid fortification. To corroborate this hypothesis, time trends in CRC incidence rates and death rates in the U.S. were plotted by age, race, and gender based on data from the Surveillance, Epidemiology, and End Results (SEER); data were analyzed by simultaneously addressing the following four critical factors: (1) a long induction period between improved folate status and potential protection of CRC; (2) a change in the U.S. Food and Drug Administration regulation in 1973 on the dose of folic acid allowed in supplements; (3) differential impacts of 1973 regulatory change and 1990s mandatory fortification by race; and (4) changes in CRC screening over time in the U.S. Although this type of analysis precludes a definitive conclusion, available evidence suggests that the increase in CRC incidence rates in the later 1990s is unlikely due to folic acid fortification and, assuming a time lag of a decade or longer to see a benefit on CRC, folate appears to be one of the most promising factors that could explain the downward trend of CRC incidence rates in the U.S.
据报道，美国是唯一发病率呈下降趋势的国家，尽管结直肠癌（CRC）的主要危险因素，包括西方饮食模式和肥胖，在美国的患病率却在上升。本文提出了一个假设，即美国叶酸状况的改善可能是最能解释这一看似矛盾现象的因素，尽管在全国范围内实施叶酸强化后，在 20 世纪 90 年代后期，CRC 的发病率暂时有所上升。为了证实这一假设，根据监测、流行病学和最终结果（SEER）的数据，按年龄、种族和性别绘制了美国 CRC 发病率和死亡率的时间趋势；通过同时解决以下四个关键因素来分析数据：（1）叶酸状况改善与 CRC 潜在保护之间的较长诱导期；（2）1973 年美国食品和药物管理局对补充剂中允许的叶酸剂量的规定发生变化；（3）种族差异对 1973 年监管变化和 20 世纪 90 年代强制性强化的影响；（4）CRC 在美国的筛查随时间的变化。尽管这种类型的分析不能得出明确的结论，但现有证据表明，20 世纪 90 年代后期 CRC 发病率的上升不太可能是由于叶酸强化所致，并且假设在看到 CRC 受益之前有十年或更长时间的时间滞后，那么叶酸似乎是最有希望的因素之一，可以解释美国 CRC 发病率下降的趋势。
