Positive Health Online

Abstract

KEY and COLLEAGUES, Cancer Epidemiology Unit, Nuffield Department of Clinical Medicine, University of Oxford, Oxford OX3 7LF,[1] Health Sciences Research Institute, Warwick Medical School, University of Warwick, Coventry CV4 7AL[2] and The Edgar National Centre for Diabetes Research and the Department of Human Nutrition, University of Otago, PO Box 56, Dunedin, New Zealand[3] studied cancer risk among meat eaters, non-meat eaters who ate fish (fish eaters) and vegetarians.

Background

Few prospective studies have examined cancer incidence among vegetarians.

Methodology

The authors studied 61,566 British men and women, comprising 32,403 meat eaters, 8,562 non-meat eaters who did eat fish ('fish eaters') and 20,601 vegetarians. After an average follow-up of 12.2 years, there were 3,350 incident cancers of which 2,204 were among meat eaters, 317 among fish eaters and 829 among vegetarians. Relative risks (RRs) were estimated by Cox regression, stratified by sex and recruitment protocol and adjusted for age, smoking, alcohol, body mass index, physical activity level and, for women only, parity and oral contraceptive use.

Results

There was significant heterogeneity in cancer risk between groups for the following four cancer sites: stomach cancer, RRs (compared with meat eaters) of 0.29 (95% CI: 0.07-1.20) in fish eaters and 0.36 (0.16-0.78) in vegetarians, P for heterogeneity=0.007; ovarian cancer, RRs of 0.37 (0.18-0.77) in fish eaters and 0.69 (0.45-1.07) in vegetarians, P for heterogeneity=0.007; bladder cancer, RRs of 0.81 (0.36-1.81) in fish eaters and 0.47 (0.25-0.89) in vegetarians, P for heterogeneity=0.05; and cancers of the lymphatic and haematopoietic tissues, RRs of 0.85 (0.56-1.29) in fish eaters and 0.55 (0.39-0.78) in vegetarians, P for heterogeneity=0.002. The RRs for all malignant neoplasms were 0.82 (0.73-0.93) in fish eaters and 0.88 (0.81-0.96) in vegetarians (P for heterogeneity=0.001).

Conclusion

The incidence of some cancers may be lower in fish eaters and vegetarians than in meat eaters.

References

TJ Key,[1] PN Appleby,[1] EA Spencer,[1] RC Travis,[1], NE Allen,[1] M Thorogood[2] and JI Mann[3]. Cancer incidence in British vegetarians. British Journal of Cancer 101: 192-197. 2009. doi:10.1038/sj.bjc.6605098 www.bjcancer.com  www.nature.com/bjc/journal/v101/n1/full/6605098a.html

Comment

The media headlines upon publication of this study trumpeted that "vegetarians were less likely to develop cancer", whereas the detailed analysis of the above study is considerably more complex and mixed, depending upon the type of cancer, as can be seen from the above results. The authors themselves disclose that this is a descriptive study, the recruitment was largely from members of the Vegetarian and Vegan Societies and their friends and families; also classification as meat, fish eater or vegetarian, was based upon the answers to 4 questions on the food frequency questionnaire. There were also questions relating to egg and dairy consumption which would include people as vegetarian rather than vegan, but in this study not meat eaters, although eggs and dairy products derive from animals. The full paper is available to download from the above website and I would encourage all interested individuals to study this paper as an illustration of how difficult it is to do this type of nutritional research in people.