Stomach cancer risk differed significantly between the dietary groups, and was significantly lower in the vegetarians than in the meat eaters, with a similar (non-significantly) low risk among the fish eaters. This observation was based on only 49 cases of stomach cancer. Previous research has suggested that processed meat may increase the risk for stomach cancer, perhaps due to the presence of N-nitroso compounds (Forman and Burley, 2006). Therefore, it is plausible that a meat-free diet could be associated with a reduction in the risk for stomach cancer. There is also some evidence that a high intake of fruit and vegetables might reduce the risk for stomach cancer, but the data are not consistent (Forman and Burley, 2006) and, although on average vegetarians eat more fruit and vegetables than meat eaters, the difference in intake is modest (Key et al, 2009).
The risk for cancer of the cervix was significantly higher among vegetarians than among meat eaters, with a similar (non-significantly) high risk among the fish eaters. The principal cause of cervical cancer is human papillomavirus. Dietary factors have been suspected of influencing risk, but no firm conclusions have been drawn (García-Closas et al, 2005). The increased risks observed in non-meat eaters were based on only 50 cases overall and might be due to non-dietary factors, such as differences in attendance for cervical cancer screening, or to chance.
The risk for ovarian cancer differed significantly between the dietary groups, and was significantly lower among fish eaters than among meat eaters. In a review, Schulz et al (2004) concluded that high meat consumption may be associated with an increased risk of ovarian cancer. The likely mechanism for such an effect is not clear, and the differences in the risk for ovarian cancer, which we observed, could be due to chance or due to differences in reproductive factors beyond the simple categories of parity and oral contraceptive use for which we were able to adjust.
Prostate cancer risk did not differ significantly between the dietary groups, although there was a significantly lower risk among fish eaters compared with meat eaters. The role of diet in the aetiology of prostate cancer is poorly understood; there is some evidence that high intakes of dairy products might be associated with an increase in risk (Chan et al, 2005), but to explore this hypothesis further in our data we would need to examine the cancer rates among vegans, among whom there are currently too few cancers to be informative.
The risk for bladder cancer was lower among vegetarians than among meat eaters, based on 85 cancers overall. Some previous studies have suggested that certain meats, such as bacon, might increase the risk for bladder cancer, perhaps due to preformed nitrosamines (Lijinsky, 1999; Michaud et al, 2006), and this area deserves further investigation.
We observed a striking difference between the dietary groups in the risk for the group of cancers of the lymphatic and haematopoietic tissues, on the basis of 257 cancers overall. The risk for these cancers was not significantly reduced among fish eaters, but among vegetarians the risk was substantially lower than that among meat eaters. Among the three major cancer types contributing to this grouping, the risks for non-Hodgkin's lymphoma and multiple myeloma, but not leukaemia, were significantly lower in vegetarians than in meat eaters. Previous research has suggested inconsistently that consumption of meat and/or exposure to live animals and raw meat among farmers and butchers might be associated with an increased risk for some of these cancers (Zhang et al, 1999; Alexander et al, 2007). Potential mechanisms could include mutagenic compounds and viruses (Cross and Lim, 2006; Alexander et al, 2007).
We did not observe any significant difference in the incidence of colorectal cancer between the dietary groups. Our earlier publications from the Oxford Vegetarian Study and EPIC-Oxford also did not report a reduction in risk for colorectal cancer among vegetarians (Sanjoaquin et al, 2004; Key et al, 2009). We also noted previously in EPIC-Oxford, that the incidence of colorectal cancer among vegetarians was identical to that in the general population of England and Wales (standardised incidence ratio 102% (95% CI: 80–129); Key et al, 2009). In the Adventist Health Study, a lower risk for colon cancer was observed among vegetarians compared with non-vegetarians (rectal cancer was not reported; Fraser, 1999). In our pooled analysis of mortality in five prospective studies, comprising the Adventist Mortality Study, the Adventist Health Study, the Health Food Shoppers Study, the Oxford Vegetarian Study and the Heidelberg Study, we observed no difference between vegetarians and non-vegetarians in mortality from colorectal cancer (Key et al, 1999). The 2007 report from the WCRF/AICR concluded that the evidence that high intakes of red and processed meat cause colorectal cancer is convincing (WCRF/AICR, 2007). In the largest single prospective study on this relationship, Cross et al (2007) reported that the risk for colorectal cancer was increased by 20% at moderate red meat intakes (equivalent to ~86 g per day in men and ~44 g per day in women). Meat intake among meat eaters in EPIC-Oxford was estimated as 78.1 and 69.7 g per day in men and women, respectively (Key et al, 2009), lower than intakes reported in the National Diet and Nutrition Survey for the United Kingdom, but still providing a substantial difference in intake between meat eaters and non-meat eaters. It is possible that this study did not have enough power to detect a moderate reduction in the risk for colorectal cancer among vegetarians, but our null findings on vegetarians suggest that the relationship of meat with the risk for colorectal cancer requires further research.
Total cancer incidence was significantly lower among both fish eaters and vegetarians than among meat eaters. This difference in total cancer incidence between meat eaters and non-meat eaters could not be ascribed to any one of the major cancer sites examined. We are unaware of other data comparing total cancer incidence in meat eaters and non-meat eaters, and the reason for this small difference is not known. More data are needed to further our understanding of this observation, which if confirmed is likely to be due to differences for specific cancer sites.
In conclusion, this study suggests that the incidence of all malignant neoplasms combined may be lower among both fish eaters and vegetarians than among meat eaters. The most striking finding was the relatively low risk for cancers of the lymphatic and haematopoietic tissues among vegetarians.
选择“Disable on www.wenxuecity.com”
选择“don't run on pages on this domain”
