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Vindication for the ecologic approach

William B. Grant   (26 July 2003)

Vindication for the ecologic approach 26 July 2003
William B. Grant, NASA Langley Research Center (this work is independent of NASA duties) 12 Sir Francis Wyatt Place, Newport News, VA 23606-3660, USA Send response to journal: Re: Vindication for the ecologic approach	The ecologic approach has not enjoyed a good reputation among the health research community. It is considered the least reliable in comparison with case-control and cohort approaches. Despite the important findings using the ecologic approach including the role of fiber in reducing the risk of colorectal cancer,1 animal fat as a risk factor for a number of cancers,2 and solar UV-B radiation through the production of vitamin D as an important risk reduction factor for colon (and other) cancer,3 an influential paper by Doll and Peto4 essentially banished the ecologic approach from serious consideration in epidemiologic studies. It was claimed that the ecologic approach was capable only of generating hypotheses. The term "ecologic fallacy" was coined to indicate that a correlation found using the ecologic approach could be due to some unmodeled factor. So, since the case-control and cohort approaches deal with real people, real food and other factors, and real disease outcomes, they ascended and enjoyed high acclaim in the health community. Only trouble was, they generally couldn't confirm such things as the link between fiber and reduced risk for colorectal cancer or animal fat as a risk factor for breast or colon cancer, to some consternation.5-7 Oh, sure, occasional studies did confirm these or related factors, but meta-analyses of such studies generally found no such link.8,9 Now, fast forward to 2003. In May we have 2 papers reporting that fiber is a risk factor for colorectal cancer,10,11 followed in July with 2 papers finding a link between animal fat and breast cancer.12,13 There are at least 2 reasons why things have changed: 1 - larger ranges of values for the important factors are included in the more successful studies; and 2 - problems with the food consumption recall approach are being realized. One reason why the ecologic approach has been so successful is that it generally includes both a large range of values as well as a very large population sample. In addition, it costs practically nothing to do the studies since they can be done using publicly available data, as I have often shown.14-17 As to going from association to causality, the criteria laid down by Sir Austin B. Hill in 1965 generally serve this purpose well.18 It even turns out that the "ecologic fallacy" argument is often a "red herring" as I've shown regarding solar UV-B radiation and cancer mortality rates in the U.S. My paper in which just UV-B radiation was used was challenged since I hadn't included other factors.17 I have now included a number of other factors and can now show that solar UV-B radiation is a risk reduction factor for 13 cancers and that the annual number of premature deaths from internal cancers in the U.S. is 30-35,000, basing the calculation on cancer mortality rates in the rural southwest [Grant, submitted]. In the future it is hoped that more credence will be given to the ecologic approach, and that those undertaking expensive and lengthy case- control or cohort studies will avail themselves of a simple ecologic study to check for feasibility and factors that should be addressed. One of the limitations of the ecologic approach that I'll admit to is that data are not readily available for some important health and disease factors, but when it comes to the major dietary factors and solar UV-B radiation, I'd put my efforts into the ecologic approach before deciding whether to invest a penny in a case-control or cohort study. References 1. Burkitt DP. Epidemiology of cancer of the colon and rectum. Cancer. 1971;28:3-13. 2. Armstrong B, Doll R. Environmental factors and cancer incidence and mortality in different countries, with special reference to dietary practices. Int J Cancer. 1975;15:617-31. 3. Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? Int J Epidemiol. 1980;9:227-31. 4. Doll R, Peto R. The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today. J Natl Cancer Inst. 1981;66:1191-1308. 5. Willett WC. Specific fatty acids and risks of breast and prostate cancer: dietary intake. Am J Clin Nutr. 1997;66:1557S-1563S. 6. Willett WC. Dietary fat intake and cancer risk: a controversial and instructive story. Semin Cancer Biol. 1998;8:245-53. 7. Fuchs CS, Giovannucci EL, Colditz GA, Hunter DJ, Stampfer MJ, Rosner B, Speizer FE, Willett WC. Dietary fiber and the risk of colorectal cancer and adenoma in women. N Engl J Med. 1999;340:169-76. 8. Smith-Warner SA, et al., Types of dietary fat and breast cancer: a pooled analysis of cohort studies. Int J Cancer. 2001;92:767-74. 9. Zock PL. Dietary fats and cancer. Curr Opin Lipidol. 2001;12:5-10. 10. Bingham SA, et al., Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet. 2003;361:1496-501. 11. Peters U, et al., Dietary fibre and colorectal adenoma in a colorectal cancer early detection programme. Lancet. 2003;361:1491-5. 12. Bingham SA, Luben R, Welch A, Wareham N, Khaw, KT, Day N. Are imprecise methods obscuring a relation between fat and breast cancer? Lancet 2003;362:212-4. 13. Cho E, Spiegelman D, Hunter DJ, Chen WY, Stampfer MJ, Colditz GA, Willett WC. Premenopausal fat intake and risk of breast cancer. J Natl Cancer Inst. 2003;95:1079-85. 14. Grant WB. Dietary links to Alzheimer's disease. Alz Dis Rev 1997;2:42-55 http://www.mc.uky.edu/adreview/Vol2/Grant/grant.pdf 15. Grant WB. Dietary fiber and colorectal cancer. The Townsend Letter. 1999;192:112-3 16. Grant WB. An ecologic study of dietary and solar ultraviolet-B links to breast carcinoma mortality rates. Cancer. 2002;94:272-81. 17. Grant WB. An estimate of premature cancer mortality in the United States due to inadequate doses of solar ultraviolet-B radiation. Cancer. 2002;94:1867-75. 18. Hill AB. The environment and disease: Association or causation?, Proc. Roy. Soc. Med. 1965;58:295-300. Competing interests:   None declared