有効と考えられている大腸癌の予防法は次の二つです。
- 野菜を多くとり、肉をなるべくとらない。お酒とタバコを控えて運動を毎日する。
- 時々大腸内視鏡をうけて大腸癌の元であるポリープを切除する
肉食と大腸癌の密接な関係は疫学的に確実です。
お酒は特にビールが一番悪いといわれています。タバコは肺癌ほど直接に関係ある訳ではありません。最近、メカニズムは不明なのですが、運動が大腸癌を予防することがわかりました。
その他、アスピリン、βカロチン、などにも予防効果があるという人もいますが広く認められている訳ではありません。
大腸ポリープは大腸癌の元であることが細胞の遺伝子を調べることで確認されてました。
そしてポリープを切除してしまえば大腸癌の大部分（７ー９割）は予防できるという臨床研究の報告があります。
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N Engl J Med 1993 Dec 30;329(27):1977-1981 Prevention of colorectal cancer
by colonoscopic polypectomy. The National Polyp Study Workgroup. Winawer SJ,
Zauber AG, Ho MN, O'Brien MJ, Gottlieb LS, Sternberg SS, Waye JD, Schapiro
M, Bond JH, Panish JF, et al Gastroenterology and Nutrition Service, Memorial
Sloan-Kettering Cancer Center, New York, NY 10021. BACKGROUND. The current
practice of removing adenomatous polyps of the colon and rectum is based on
the belief that this will prevent colorectal cancer. To address the hypothesis
that colonoscopic polypectomy reduces the incidence of colorectal cancer,
we analyzed the results of the National Polyp Study with reference to other
published results. METHODS. The study cohort consisted of 1418 patients who
had a complete colonoscopy during which one or more adenomas of the colon
or rectum were removed. The patients subsequently underwent periodic colonoscopy
during an average follow-up of 5.9 years, and the incidence of colorectal
cancer was ascertained. The incidence rate of colorectal cancer was compared
with that in three reference groups, including two cohorts in which colonic
polyps were not removed and one general-population registry, after adjustment
for sex, age, and polyp size. RESULTS. Ninety-seven percent of the patients
were followed clinically for a total of 8401 person-years, and 80 percent
returned for one or more of their scheduled colonoscopies. Five asymptomatic
early-stage colorectal cancers (malignant polyps) were detected by colonoscopy
(three at three years, one at six years, and one at seven years). No symptomatic
cancers were detected. The numbers of colorectal cancers expected on the basis
of the rates in the three reference groups were 48.3, 43.4, and 20.7, for
reductions in the incidence of colorectal cancer of 90, 88, and 76 percent,
respectively ( これは、N Engl J Medという医学誌に１９９３年に発表された論文の要旨です。大腸ポリープを内視鏡にて切除することで大腸癌の大部分（８から９割）が予防されるということが、結論です。