Comparison of 4 established DASH diet indexes: examining associations of index scores and colorectal cancer 1–3 Paige E Miller, Amanda J Cross, Amy F Subar, Susan M Krebs-Smith, Yikyung Park, Tiffany Powell-Wiley, Albert Hollenbeck, and Jill Reedy ABSTRACT Background: Multiple diet indexes have been developed to capture the Dietary Approaches to Stop Hypertension (DASH) dietary pat- tern and examine relations with health outcomes but have not been compared within the same study population to our knowledge. Objective: We compared 4 established DASH indexes and exam- ined associations with colorectal cancer. Design: Scores were generated from a food-frequency questionnaire in the NIH-AARP Diet and Health Study (n = 491,841). Separate indexes defined by Dixon (7 food groups, saturated fat, and alco- hol), Mellen (9 nutrients), Fung (7 food groups and sodium), and Gu ¨ nther (8 food groups) were used. HRs and 95% CIs for colorectal cancer were generated by using Cox proportional hazard models. Results: From 1995 through 2006, 6752 incident colorectal cancer cases were ascertained. In men, higher scores were associated with reduced colorectal cancer incidence by comparing highest to lowest quintiles for all indexes as follows: Dixon (HR: 0.77; 95% CI: 0.69, 0.87), Mellen (HR: 0.78; 95% CI: 0.71, 0.86), Fung (HR: 0.75; 95% CI: 0.68, 0.83), and Gu ¨ nther (HR: 0.81; 95% CI: 0.74, 0.90). Higher scores in women were inversely associated with colorectal cancer incidence by using methods defined by Mellen (HR: 0.79; 95% CI: 0.68, 0.91), Fung (HR: 0.84; 95% CI: 0.73, 0.96), and Gu ¨ nther (HR: 0.84; 95% CI: 0.73.0.97) but not Dixon (HR: 1.01; 95% CI: 0.80, 1.28). Conclusion: The consistency in findings, particularly in men, sug- gests that all indexes capture an underlying construct inherent in the DASH dietary pattern, although the specific index used can affect results. Am J Clin Nutr 2013;98:794–803. INTRODUCTION Epidemiologic studies have traditionally assessed effects of single nutrients, foods, and other individual dietary constituents on cancer risk. Research that has used this approach is valuable for understanding potential biological mechanisms that underlie observed associations, but it has been limited by the multi- collinearity of dietary intake variables and the inability to detect small effects of single dietary components (1). The investigation of dietary patterns or overall diet quality is a promising com- plementary approach to help overcome some of these limitations (1–4) and provide useful information for developing guidelines and public health recommendations. National and international cancer organizations have recommend a largely plant-based dietary pattern that is rich in fruits, vegetables, whole grains, and legumes and low in red and processed meat, refined grains, added sugar, and energy density for cancer prevention (5). The 2010 Dietary Guidelines for Americans also provided similar recommendations based on dietary patterns, with the addition of low-fat dairy products, to promote health and reduce risk of chronic disease, including cancer. This guidance has suggested 2 eating patterns, the USDA Food Patterns and the Dietary Ap- proaches to Stop Hypertension (DASH) 4 Eating Plan, the latter of which aligns with the DASH diet that was examined in 2 multicenter, randomized controlled feeding trials (6, 7). The first DASH trial showed that a diet rich in fruit, vegetables, and low-fat dairy products and reduced in saturated and total fat (labeled the DASH diet) significantly reduced blood pressure (6). A follow-up trial, entitled the DASH-Sodium Trial, showed that a reduction of sodium intake in conjunction with the original DASH diet further reduced blood pressure (7). This sodium- reduced DASH diet represents an overall dietary pattern because it aims to encompass the whole diet, including combinations of foods and nutrients consumed together. Although this dietary pattern was originally designed to reduce hypertension and cardiovascular disease risk, it may have relevance to colorectal cancer prevention, particularly because several of its character- istics, such as high fruit and vegetable intake and reduced intake of meat, have been implicated in the cause of this malignancy. Associations between an adherence to a DASH dietary pattern, assessed by scores on DASH diet indexes, and different end- points, such as diabetes (8), coronary heart disease (9), colorectal adenoma (10), and colorectal cancer (11), have been evaluated previously. However, these earlier studies have operationalized 1 From the Cancer Prevention Fellowship Program (PEM) and the Divi- sions of Cancer Epidemiology and Genetics (AJC and YP) and Cancer Control and Population Sciences (AFS, SMK-S, and JR), National Cancer Institute, Rockville, MD; the Center for Epidemiology, Biostatistics, and Computational Biology, Exponent Inc, Chicago, IL (PEM); the Cardiovas- cular and Pulmonary Branch, National Heart, Lung, and Blood Institute, Bethesda, MD (TP-W); and the AARP, Washington, DC (AH). 2 Supported by the Cancer Prevention Fellowship Program and the Intra- mural Research Program, National Cancer Institute, NIH. 3 Address reprint requests and correspondence to PE Miller, Exponent Inc, 525 West Monroe Street, Suite 1050, Chicago, IL 60661. E-mail: pmiller@ exponent.com. 4 Abbreviations used: DASH, Dietary Approaches to Stop Hypertension; FFQ, food-frequency questionnaire; MPED, MyPyramid Equivalents Database. Received March 31, 2013. Accepted for publication May 30, 2013. First published online July 17, 2013; doi: 10.3945/ajcn.113.063602. 794 Am J Clin Nutr 2013;98:794–803. Printed in USA. Ó 2013 American Society for Nutrition by guest on April 21, 2016 ajcn.nutrition.org Downloaded from