© 2005 Oxford University Press
CORRESPONDENCE |
RESPONSE: Re: Meat, Fish, and Colorectal Cancer Risk: The European Prospective Investigation into Cancer and Nutrition
Affiliations of authors: Infections and Cancer Epidemiology Group, International Agency for Research on Cancer, Lyon, France (TN); Medical Research Council Dunn Human Nutrition Unit, Cambridge, UK (SB); Nutrition and Hormones Group, International Agency for Research on Cancer, Lyon, France (ER)
Correspondence to: Elio Riboli, MD, MPH, ScM, International Agency for Research on Cancer, 150 cours Albert Thomas, 69372, Lyon Cedex 08, France (e-mail: riboli{at}iarc.fr).
Batty suggests that our findings of a positive association between high intake of red and processed meat and colorectal cancer risk might be the result of confounding by socioeconomic position. In our study population, meat intake is inversely associated with educational attainment (1), an indicator of socioeconomic position. The relative risks of colorectal cancer associated to secondary school, professional school, and university compared with primary school or less were 1.00, 1.12, and 1.02, respectively, indicating that colorectal cancer risk does not vary by educational attainment in this population. It is therefore not surprising that adjustment for educational attainment did not modify the relationship of red meat, processed meat, and fish with colorectal cancer risk. We have previously shown that the inverse association of colorectal cancer risk with fiber intake persisted after adjustment for this indicator of socioeconomic status (2).
We appreciate the fact that initial results based on a relatively small number of cancer patients may change when precision increases with longer follow-up and when confounding is attenuated by better adjustment for covariates, as may have been the case for the study (3) cited by Batty. The number of colorectal cancer case patients in the European Prospective Investigation into Cancer and Nutrition (EPIC) study is comparable to the number included in the recent combined analysis of the Nurses' Health Study and the Health Professionals Follow Up Study (3), and our results are adjusted for main potential confounders. The cohorts in EPIC are heterogeneous in diet, lifestyle, and other potential confounders (4), but there was not a statistically significant heterogeneity in the association of red and processed meat with colorectal cancer risk when the analyses were conducted by country (Pheterogeneity = .82).
Gonder and Worm ask why we did not mention in the abstract that red meat alone does not statistically significantly increase the relative risk of colorectal cancer. The association of red meat with colorectal cancer was statistically significant when the variable was modeled as continuous (Ptrend = .03) and close to statistical significance in categorical models (Ptrend = .08). These results do not provide evidence of a lack of association of high consumption of red meat and colorectal cancer risk. As discussed in our article, previous studies have provided possible explanations for the association with red meat, processed and unprocessed, but not with processed meat only. One possibility could be increased exposure to N-nitroso compounds and their precursors due to nitrites or nitrates added to meat for preservation. However, not all processed meats contain added nitrites, and we could not identify one particular type of processed meat that was more strongly associated with colorectal cancer risk than others.
Gonder and Worm ask why our analyses were not adjusted for vegetables, good sources of fiber and folate. Adjustment for vegetables did not modify our results, and this variable was not kept in the model. Our results were adjusted for fiber intake, and we showed that they were unchanged after adjustment for dietary folate in a subset of the cohort for whom dietary folate was available. As noted in the correspondence, there was some evidence that the association of red and processed meat with colorectal cancer risk might be weaker in the group of subjects with higher intake of fiber. Because, to the best of our knowledge, this possible modification by fiber of the association between meat intake and colorectal cancer risk had not been previously reported by large prospective studies, further research is needed before drawing any firm conclusions.
Finally, we see as a strong point supporting our results the fact that there was no heterogeneity of the association for red and processed meat across countries in EPIC, despite the high variability of vegetable and fiber consumption across EPIC cohorts (5). Our results support our conclusion that red and processed meat are positively associated with risk of colorectal cancer, but they do not demonstrate that high intake of red meat accompanied by high intake of vegetables is not associated with colorectal cancer risk.
REFERENCES
(1) Linseisen J, Kesse E, Slimani N, Bueno-De-Mesquita HB, Ocke MC, Skeie G, et al. Meat consumption in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohorts: results from 24-hour dietary recalls. Public Health Nutr 2002;5:1243–58.[CrossRef][Web of Science][Medline]
(2) Bingham SA, Norat T, Moskal A, Ferrari P, Slimani N, Clavel-Chapelon F, et al. Is the association with fiber from foods in colorectal cancer confounded by folate intake? Cancer Epidemiol Biomarkers Prev 2005;14:1552–6.
(3) Wei EK, Giovannucci E, Wu K, Rosner B, Fuchs CS, Willett WC, et al. Comparison of risk factors for colon and rectal cancer. Int J Cancer 2004;108:433–42.[CrossRef][Web of Science][Medline]
(4) Bingham S, Riboli E. Diet and cancer. The European Prospective Investigation into Cancer and Nutrition. Nat Rev Cancer 2004;4: 206–15.[CrossRef][Web of Science][Medline]
(5) Agudo A, Slimani N, Ocke MC, Naska A, Miller AB, Kroke A, et al. Consumption of vegetables, fruit and other plant foods in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohorts from 10 European countries. Public Health Nutr 2002;5:1179–96.[CrossRef][Web of Science][Medline]
Related Correspondence
CiteULike 
Connotea 
Del.icio.us What's this?
J Natl Cancer Inst 2005 97: 1787.
J Natl Cancer Inst 2005 97: 1788.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||