Abstract
Background: Although the Mediterranean diet has been studied for cancer mortality and the Dietary Approaches to Stop Hypertension (DASH) diet shares similarities with the Mediterranean diet, few studies have specifically examined these 2 diets and incident colorectal cancer.
Objective: The objective was to prospectively assess the association between the Alternate Mediterranean Diet (aMed) and the DASH-style diet scores and risk of colorectal cancer in middle-aged men and women.
Design: A total of 87,256 women and 45,490 men (age 30–55 y for women and 40–75 y for men at baseline) without a history of cancer were followed for ≤26 y. The aMed and DASH scores were calculated for each participant by using dietary information that was assessed ≤7 times during follow-up. Relative risks (RRs) for colorectal cancer were computed with adjustment for potential confounders.
Results: We documented 1432 cases of incident colorectal cancer among women and 1032 cases in men. Comparing top with bottom quintiles of the DASH score, the pooled RR for total colorectal cancer was 0.80 (95% CI: 0.70, 0.91; P for trend = 0.0001). The corresponding RR for DASH score and colon cancer was 0.81 (95% CI: 0.69, 0.95; P for trend = 0.002). There was a suggestion of an inverse association with rectal cancer with a pooled RR of 0.73 (95% CI: 0.55, 0.98; P for trend = 0.31) when comparing top with bottom quintiles of DASH score. No association was observed with aMed score.
Conclusion: Adherence to the DASH diet (which involves higher intakes of whole grains, fruit, and vegetables; moderate amounts of low-fat dairy; and lower amounts of red or processed meats, desserts, and sweetened beverages) was associated with a lower risk of colorectal cancer.
INTRODUCTION
The traditional Mediterranean diet is characterized by high intakes of fruit, vegetables, fish, and whole grains; moderate amounts of alcohol and dairy products; and low amounts of red or processed meats and sweets (1). Higher intake of whole grains may reduce the risk of colorectal cancer, although results have been inconsistent (2, 3). On the other hand, high red or processed meat intake has been associated consistently with a higher risk of colorectal cancer (4). Therefore, adherence to the traditional Mediterranean diet may confer a reduced risk of colorectal cancer. Various Mediterranean diet scores have been created to measure adherence, with consistent results that this diet is associated with a lower risk of cancer mortality (5) and prevalent colorectal adenoma (6). In one prospective study, adherence to the Mediterranean diet was inversely associated with incidence of colorectal cancer (7).
The Dietary Approaches to Stop Hypertension (DASH) diet features high intakes of fruit, vegetables, legumes, and nuts; moderate amounts of low-fat dairy products; and low amounts of animal protein and sweets; and sodium reduction is now part of the diet (8). Although the DASH diet was originally designed for blood pressure reduction, several characteristics, such as higher intakes of whole grain and lower intakes of red and processed meat, are similar to the Mediterranean diet and may suggest a potential for colorectal cancer risk reduction. Dairy products have been shown to lower the risk of colorectal cancer (9). Although the DASH diet has been previously shown to associate with reduced odds of prevalent colorectal adenomas (6), its association with incident colorectal cancer has not been examined.
We previously developed dietary scores to measure adherence to the Mediterranean diet (10) and the DASH diet (11) in the Nurses' Health Study (NHS) and Health Professionals Follow-Up Study (HPFS). In the current analysis, we prospectively examined the association between diet scores and risk of colorectal cancer in these 2 large ongoing cohorts of men and women. We also separately considered specific anatomic sites of tumor location.
SUBJECTS AND METHODS
Study population
The NHS is a cohort study of 121,700 female nurses aged 30–55 y living in 11 US states at the time of inception in 1976. The first questionnaire regarding medical, lifestyle, and other health-related information was sent at the time of inception (12). Since then, questionnaires have been sent biennially to update this information. In 1980, participants completed a 61-item food-frequency questionnaire (FFQ). In 1984, the FFQ was expanded to 116 items, and similar FFQs were sent in 1986, 1990, 1994, 1998, and 2002.
The HPFS was established in 1986 with 51,529 male podiatrists, optometrist, pharmacists, dentists, and veterinarians aged 40–75 y. At baseline and every 2 y, a questionnaire on medical, lifestyle, and other health-related information was sent to the cohort members. A validated self-administered FFQ with ≈140 items was sent in 1986 and every 4 y to obtain dietary information (13). Follow-up was complete for >90% in each 2-y cycle for both cohorts.
For this analysis, we used 1980 as baseline for the NHS, because that is the year when the first dietary data were collected. We included women who completed the 1980 FFQ with <10 missing items and who had a realistic total energy intake (as calculated from the FFQ, between 500 and 3500 kcal/d) (14). For the HPFS, we included men with an FFQ with total energy intake (as calculated from the FFQ) between 800 and 4200 kcal/d at baseline and who had <70 missing items. After excluding individuals with a history of cancer (except for nonmelanoma skin cancer) and ulcerative colitis at baseline, we included 87,312 women and 45,080 men in this analysis. This study was approved by the Institutional Review Board of the Brigham and Women's Hospital and the Harvard School of Public Health, Boston, MA.
Dietary assessment
Self-administered, semiquantitative FFQs were designed to assess average food intake over the preceding year. A standard portion size and 9 possible frequency-of-consumption responses, ranging from “never, or less than once per month” to “6 or more times per day” were given for each food. Total energy and nutrient intake was calculated by summing up energy or nutrients from all foods. Previous validation studies in this cohort revealed reasonably good correlations between energy-adjusted nutrients assessed by the FFQ and multiple weeks of food records completed over the preceding year in both the NHS (14) and the HPFS (13). In the NHS, the deattenuated correlation coefficient between diet records and FFQ ranged from 0.48 for polyunsaturated fat to 0.79 for vitamin A. The mean correlation coefficient between frequencies of intake of 55 foods assessed by 2 FFQs 12 mo apart was 0.57 (14, 15). In the HPFS, the deattenuated correlation coefficient between FFQ and diet records ranged from 0.32 for protein to 0.81 for vitamin B-6.
Computation of the Alternate Mediterranean Diet (aMed) (10) and DASH (11) scores has been previously described in detail. We calculated each score for each FFQ and each participant. Briefly, the aMed rewards 1 point if intake is above the cohort-specific median for vegetables, legumes, fruit, nuts, whole-grain cereals, fish, and monounsaturated:saturated fat ratio and 1 point for intake below the cohort-specific median for red and processed meats (10). Alcohol intake of 5–15 g/d for women and 10–25 g/d for men received 1 point. The DASH score rewards points for high intake of fruit, vegetables, nuts and legumes, low-fat dairy products, and whole grains according to quintile rankings (ie, participants in the lowest quintile are assigned 1 point and those in the highest quintile are assigned 5 points). On the other hand, with regard to intake of sodium, sweetened beverages, and red and processed meats, participants with lower quintiles of intake scored higher points (ie, the lowest quintile received a score of 5 and the highest a score of 1) (11). The total possible score range was 8–40.
Ascertainment of colorectal cancer
Incident colorectal cancer was ascertained between 1980 and 2006 for the NHS and between 1986 and 2006 for the HPFS. In each biennial questionnaire, participants self-report any diagnosis of colorectal cancer in the previous 2 y. We then sought permission to obtain medical records to confirm the diagnosis. Physicians unaware of dietary and lifestyle data reviewed and recorded information on histology, site, and stage of the cancer. Only adenocarcinomas of the colorectum were included, but we excluded cases associated with ulcerative colitis and familiar polyposis. The follow-up for death in both cohorts is ≥95% complete (16).
Covariate ascertainment
Body mass index (BMI) was calculated from weight reported on each biennial questionnaire and height reported at the first questionnaire. Smoking, history of hypertension, aspirin use, multivitamin intake, menopausal status and use of postmenopausal hormone therapy, parity, and age at first birth were assessed every 2 y. In the NHS, information on hours per week of vigorous activity was collected in 1980, 1982, and 1984. Leisure-time physical activity was measured 7 times beginning in 1986 with validated questions on 10 common activities in the NHS and biennially from baseline in the HPFS. The information was then summed and calculated as metabolic equivalent task hours (METs) (17). In the NHS, we inquired about physical examinations at baseline and in both cohorts every 2 y beginning in 1988. Family history of colorectal cancers and information on lower bowel endoscopy screening were also collected. Deaths were identified from state vital statistics records, the National Death Index, and the postal system and as reported by the families.
Statistical analysis
We used Cox proportional hazard models to assess the association between the DASH and aMed scores and risk of colorectal cancer during follow-up. Proportional hazard assumption was tested with use of interaction terms between the diet scores and age and was found not to be violated (P > 0.05). To reduce random within-person variation and to best represent long-term dietary intake, we calculated cumulative averages of the DASH and aMed scores from our repeated FFQs (18). For example, in the NHS, the diet scores in 1980 were used to predict colorectal cancer risk between 1980 and 1984, the average score from 1980 and 1984 was used to predict colorectal cancer from 1984 to 1986, and so forth. The same procedure was used in the HPFS.
In multivariate analyses, we adjusted for age (by stratifying age in months in the Cox model), physical activity (quintiles), BMI (5 categories), energy intake (quintiles), alcohol intake (4 categories, DASH score only), history of colorectal polyps (yes or no), family history of colorectal cancer (yes or no), history of lower bowel endoscopy (yes or no), aspirin use (yes or no), pack-years of smoking (5 categories), and multivitamin use (yes or no) with updated information at each 2-y questionnaire cycle. Test of trend was conducted by fitting continuous terms for the 2 diet scores. We also examined associations separately by tumor location (colon, proximal colon and distal colon, rectum).
To assess the contribution of each of the individual components of the DASH diet, we simultaneously modeled each component individually. In separate models, we also included the overall DASH score. The difference in relative risks (RRs) of the DASH score between models with or without the food component can be interpreted as the contribution of the food component on colorectal cancer risk. RRs from each cohort were also pooled to obtain a summary risk estimate by using a random-effects model that allows for between-study heterogeneity (19). P values for heterogeneity of study results were calculated by using the Cochran Q test. The statistical analysis was conducted with SAS version 9 (SAS Institute, Cary, NC).
RESULTS
In ≤26 y of follow-up in the NHS, we documented 1432 cases of incident colorectal cancer, of which 1082 were colon cancer and 323 were rectal cancer; the rest were not clearly classified for subsite. In the HPFS, with ≤20 y of follow-up, we documented 1032 cases of incident colorectal cancer, of which 682 were colon cancer and 218 were rectal cancer; the rest were not clearly classified for subsite.
The aMed and DASH scores were substantially correlated. Spearman's correlation coefficients for cumulative average aMed and DASH score were 0.74 (P < 0.0001) for the NHS and 0.75 (P < 0.0001) for the HPFS. As shown in Tables 1 and 2, we compared baseline lifestyle characteristics and dietary intake between DASH or aMed. Because of the long follow-up in women, we present the 1990 dietary data, because it is close to the midpoint of follow-up. Men and women who scored higher in either the aMed or DASH were less likely to smoke but more likely to use multivitamins regularly and were more active (Tables 1 and 2). Men with higher aMed and DASH scores tended to be leaner, but this was less apparent among women.
TABLE 1.
Age-standardized baseline (1980) characteristics and 1990 dietary intake according to quintiles (Q) of Alternate Mediterranean Diet (aMed) and Dietary Approaches to Stop Hypertension (DASH) scores among women (n = 87,312)1
| aMed |
DASH |
|||||
| Q1 | Q3 | Q5 | Q1 | Q3 | Q5 | |
| Score | 2 (1–2)2 | 4 (4–4) | 6 (6–9) | 17 (8–19) | 24 (23–25) | 30 (29–38) |
| 1980 Characteristics | ||||||
| BMI (kg/m2) | 24.5 ± 0.013 | 24.4 ± 0.01 | 24.2 ± 0.01 | 24.5 ± 0.01 | 24.4 ± 0.01 | 24.1 ± 0.01 |
| Current smokers (%) | 35 ± 0.001 | 28 ± 0.001 | 20 ± 0.001 | 39 ± 0.001 | 28 ± 0.001 | 19 ± 0.001 |
| Multivitamin use (%) | 28 ± 0.001 | 34 ± 0.001 | 41 ± 0.001 | 26 ± 0.001 | 34 ± 0.001 | 42 ± 0.001 |
| Physical activity (METs/wk) | 11 ± 0.05 | 14 ± 0.05 | 18 ± 0.05 | 10 ± 0.05 | 14 ± 0.04 | 19 ± 0.05 |
| Family history (%) | 11 ± 0.001 | 12 ± 0.001 | 12 ± 0.001 | 12 ± 0.001 | 12 ± 0.001 | 12 ± 0.001 |
| 1990 Dietary intake4 | ||||||
| Energy (kcal) | 1514 ± 1.1 | 1740 ± 1.2 | 2004 ± 1.1 | 1693 ± 1.3 | 1740 ± 1.1 | 1865 ± 1.3 |
| Alcohol (g) | 5 ± 0.02 | 5 ± 0.02 | 6 ± 0.02 | 6 ± 0.02 | 5 ± 0.02 | 4 ± 0.02 |
| Fiber (g) | 14 ± 0.01 | 18 ± 0.01 | 22 ± 0.01 | 13 ± 0.01 | 18 ± 0.01 | 24 ± 0.01 |
| Animal protein (g) | 56 ± 0.03 | 56 ± 0.04 | 55 ± 0.03 | 54 ± 0.04 | 56 ± 0.03 | 56 ± 0.04 |
| Vegetable protein (g) | 18 ± 0.01 | 20 ± 0.01 | 23 ± 0.01 | 17 ± 0.01 | 20 ± 0.01 | 24 ± 0.01 |
| Glycemic load | 102 ± 0.05 | 106 ± 0.05 | 109 ± 0.05 | 102 ± 0.05 | 105 ± 0.04 | 112 ± 0.05 |
| Monounsaturated fat (g) | 23 ± 0.01 | 21 ± 0.01 | 20 ± 0.01 | 24 ± 0.01 | 22 ± 0.01 | 18 ± 0.01 |
| Polyunsaturated fat (g) | 10 ± 0.01 | 11 ± 0.01 | 11 ± 0.01 | 11 ± 0.01 | 11 ± 0.01 | 10 ± 0.01 |
| Saturated fat (g) | 22 ± 0.01 | 19 ± 0.01 | 16 ± 0.01 | 22 ± 0.01 | 19 ± 0.01 | 15 ± 0.01 |
| Folate (μg) | 370 ± 0.5 | 432 ± 0.5 | 488 ± 0.5 | 331 ± 0.5 | 434 ± 0.5 | 527 ± 0.5 |
| Calcium (mg) | 951 ± 1.1 | 988 ± 1.2 | 1018 ± 1.1 | 762 ± 1.2 | 995 ± 1.1 | 1194 ± 1.2 |
1980 scores are for baseline characteristics, and 1990 scores are for dietary intake. METs, metabolic equivalent task hours.
Median; range in parentheses (all such values).
Mean ± SE (all such values).
Energy-adjusted except for alcohol and energy.
TABLE 2.
Age-standardized baseline (1986) characteristics according to quintiles (Q) of Alternate Mediterranean Diet (aMed) and Dietary Approaches to Stop Hypertension (DASH) scores among men (n = 45,080)1
| aMed |
DASH |
|||||
| Q1 | Q3 | Q5 | Q1 | Q3 | Q5 | |
| Score | 2 (0–2)2 | 4 (4–4) | 7 (7–9) | 17 (8–19) | 24 (23–25) | 31 (29–40) |
| BMI (kg/m2) | 25.9 ± 0.13 | 25.6 ± 0.1 | 25.0 ± 0.1 | 25.9 ± 0.1 | 25.6 ± 0.1 | 24.9 ± 0.1 |
| Current smokers (%) | 15 ± 0.001 | 9 ± 0.001 | 4 ± 0.001 | 16 ± 0.001 | 8 ± 0.001 | 3 ± 0.001 |
| Multivitamin use (%) | 35 ± 0.002 | 40 ± 0.002 | 50 ± 0.002 | 34 ± 0.002 | 41 ± 0.002 | 50 ± 0.002 |
| Physical activity (METs/wk) | 16 ± 0.01 | 20 ± 0.01 | 29 ± 0.01 | 15 ± 0.1 | 21 ± 0.1 | 30 ± 0.1 |
| Family history (%) | 8 ± 0.001 | 9 ± 0.001 | 9 ± 0.001 | 8 ± 0.001 | 9 ± 0.001 | 9 ± 0.001 |
| Dietary intake4 | ||||||
| Energy (kcal) | 1753 ± 2.1 | 1946 ± 2.2 | 2270 ± 2.4 | 1819 ± 2.0 | 1993 ± 2.1 | 2173 ± 2.0 |
| Alcohol (g) | 12 ± 0.05 | 11 ± 0.06 | 11 ± 0.06 | 12 ± 0.05 | 11 ± 0.05 | 9 ± 0.05 |
| Fiber (g) | 15 ± 0.02 | 20 ± 0.02 | 27 ± 0.02 | 15 ± 0.02 | 21 ± 0.02 | 28 ± 0.02 |
| Animal protein (g) | 68 ± 0.06 | 68 ± 0.06 | 66 ± 0.07 | 67 ± 0.06 | 68 ± 0.06 | 66 ± 0.06 |
| Vegetable protein (g) | 20 ± 0.02 | 24 ± 0.02 | 30 ± 0.02 | 21 ± 0.02 | 25 ± 0.02 | 30 ± 0.02 |
| Glycemic load | 116 ± 0.09 | 123 ± 0.09 | 133 ± 0.1 | 117 ± 0.08 | 123 ± 0.09 | 136 ± 0.08 |
| Monounsaturated fat (g) | 30 ± 0.02 | 28 ± 0.02 | 24 ± 0.02 | 31 ± 0.02 | 27 ± 0.02 | 23 ± 0.02 |
| Polyunsaturated fat (g) | 12 ± 0.01 | 13 ± 0.01 | 14 ± 0.01 | 13 ± 0.01 | 13 ± 0.01 | 13 ± 0.01 |
| Saturated fat (g) | 29 ± 0.02 | 25 ± 0.02 | 19 ± 0.02 | 28 ± 0.02 | 25 ± 0.02 | 20 ± 0.02 |
| Folate (μg) | 391 ± 1.0 | 463 ± 1.0 | 584 ± 1.1 | 370 ± 0.9 | 481 ± 0.9 | 598 ± 0.9 |
| Calcium (mg) | 872 ± 1.5 | 892 ± 1.5 | 922 ± 1.7 | 723 ± 1.3 | 900 ± 1.4 | 1071 ± 1.4 |
METs, metabolic equivalent task hours.
Median; range in parentheses (all such values).
Mean ± SE (all such values).
Energy-adjusted except for alcohol and energy.
A higher aMed score was associated with a similar magnitude of reduced risk of colorectal cancer in both women and men, but neither reached statistical significance. When data from both cohorts were pooled, we observed an RR of 0.89 (95% CI: 0.77, 1.01; P for trend = 0.06) for total colorectal cancer (Table 3). The association was slightly weaker for men.
TABLE 3.
Relative risks (95% CI) for colorectal cancer according to quintiles (Q) of Alternate Mediterranean Diet score (n = 87,312 for women and 45,080 for men)1
| Q1 | Q2 | Q3 | Q4 | Q5 | P for trend | |
| Total colorectal cancer | ||||||
| Men | ||||||
| No. of cases | 197 | 188 | 227 | 228 | 192 | |
| Age- and energy-adjusted | 1 | 0.91 (0.74, 1.11) | 0.99 (0.82, 1.21) | 0.90 (0.74, 1.09) | 0.77 (0.62, 0.95) | 0.008 |
| Multivariate-adjusted2 | 1 | 0.94 (0.76, 1.15) | 1.04 (0.86, 1.27) | 0.98 (0.80, 1.20) | 0.88 (0.71, 1.09) | 0.25 |
| Women | ||||||
| No. of cases | 285 | 282 | 282 | 279 | 307 | |
| Age- and energy-adjusted | 1 | 0.92 (0.78, 1.08) | 0.79 (0.67, 0.94) | 0.79 (0.66, 0.93) | 0.79 (0.66, 0.93) | 0.002 |
| Multivariate-adjusted2 | 1 | 0.94 (0.80, 1.12) | 0.84 (0.71, 0.99) | 0.85 (0.71, 1.01) | 0.88 (0.74, 1.05) | 0.14 |
| Pooled | 1 | 0.94 (0.83, 1.07) | 0.92 (0.75, 1.13) | 0.90 (0.79, 1.02) | 0.89 (0.77, 1.01) | 0.06 |
| Colon cancer | ||||||
| Men | ||||||
| No. of cases | 130 | 115 | 153 | 152 | 132 | |
| Age- and energy-adjusted | 1 | 0.83 (0.64, 1.07) | 0.99 (0.78, 1.26) | 0.88 (0.69, 1.12) | 0.77 (0.60, 0.99) | 0.07 |
| Multivariate-adjusted2 | 1 | 0.85 (0.66, 1.09) | 1.03 (0.81, 1.31) | 0.94 (0.73, 1.20) | 0.87 (0.67, 1.13) | 0.45 |
| Women | ||||||
| No. of cases | 209 | 212 | 224 | 201 | 236 | |
| Age- and energy-adjusted | 1 | 0.92 (0.76, 1.12) | 0.85 (0.70, 1.03) | 0.77 (0.63, 0.94) | 0.81 (0.67, 0.99) | 0.007 |
| Multivariate-adjusted2 | 1 | 0.95 (0.78, 1.15) | 0.89 (0.74, 1.08) | 0.82 (0.67, 1.01) | 0.91 (0.74, 1.11) | 0.13 |
| Pooled | 1 | 0.91 (0.78, 1.06) | 0.94 (0.81, 1.10) | 0.87 (0.74, 1.02) | 0.89 (0.76, 1.05) | 0.11 |
| Rectal cancer | ||||||
| Men | ||||||
| No. of cases | 42 | 49 | 42 | 53 | 32 | |
| Age- and energy-adjusted | 1 | 1.18 (0.78, 1.79) | 0.88 (0.57, 1.37) | 1.03 (0.68, 1.56) | 0.63 (0.39, 1.02) | 0.03 |
| Multivariate-adjusted2 | 1 | 1.27 (0.83, 1.94) | 0.97 (0.62, 1.51) | 1.18 (0.77, 1.82) | 0.75 (0.46, 1.23) | 0.19 |
| Women | ||||||
| No. of cases | 70 | 67 | 53 | 70 | 63 | |
| Age- and energy-adjusted | 1 | 0.93 (0.67, 1.31) | 0.62 (0.43, 0.90) | 0.85 (0.60, 1.20) | 0.67 (0.47, 0.96) | 0.12 |
| Multivariate-adjusted2 | 1 | 0.97 (0.69, 1.36) | 0.67 (0.47, 0.97) | 0.94 (0.66, 1.34) | 0.80 (0.55, 1.15) | 0.64 |
| Pooled | 1 | 1.08 (0.83, 1.40) | 0.79 (0.55, 1.01) | 1.03 (0.79, 1.35) | 0.78 (0.58, 1.05) | 0.21 |
Relative risks were computed from a Cox proportional hazards model.
Adjusted for age (continuous), BMI (5 categories), alcohol intake (4 categories), family history (yes or no), physical activity (quintiles), aspirin use (4 categories), colonoscopy, history of polyps, multivitamin use (yes or no), pack-years of smoking (5 categories), and energy intake (quintiles).
For the DASH score, we observed an RR for total colorectal cancer of 0.80 (95% CI: 0.67, 0.94; P for trend = 0.005) when comparing the highest with lowest quintiles in women (Table 4). The magnitude of risk reduction was essentially the same among men but marginally significant due to fewer cases. The pooled RR for total colorectal cancer was 0.80 (95% CI: 0.70, 0.91; P for trend = 0.001). The association for colon cancer was slightly weaker in both men and women, but the pooled RR remained statistically significant when comparing highest with lowest quintiles (RR: 0.81; 95% CI: 0.69, 0.95; P for trend = 0.002). There was also a suggestion of an inverse association with rectal cancer with a pooled RR of 0.73 (95% CI: 0.55, 0.98) between top and bottom quintiles, but the P value for trend was not significant (P = 0.31).
TABLE 4.
Relative risks (95% CI) for colorectal cancer according to quintiles (Q) of Dietary Approaches to Stop Hypertension score (n = 87,312 for women and 45,080 for men)1
| Q1 | Q2 | Q3 | Q4 | Q5 | P for trend | |
| Total colorectal cancer | ||||||
| Men | ||||||
| No. of cases | 205 | 199 | 212 | 201 | 215 | |
| Age- and energy-adjusted | 1 | 0.80 (0.66, 0.98) | 0.81 (0.67, 0.99) | 0.72 (0.59, 0.87) | 0.68 (0.56, 0.83) | 0.0003 |
| Multivariate-adjusted2 | 1 | 0.83 (0.68, 1.08) | 0.86 (0.71, 1.05) | 0.79 (0.65, 0.97) | 0.81 (0.66, 1.00) | 0.09 |
| Women | ||||||
| No. of cases | 292 | 272 | 294 | 266 | 308 | |
| Age- and energy-adjusted | 1 | 0.79 (0.67, 0.94) | 0.80 (0.68, 0.94) | 0.70 (0.59, 0.83) | 0.71 (0.60, 0.83) | <0.0001 |
| Multivariate-adjusted2 | 1 | 0.81 (0.69, 0.96) | 0.84 (0.71, 0.99) | 0.76 (0.64, 0.90) | 0.80 (0.67, 0.94) | 0.005 |
| Pooled | 1 | 0.82 (0.72, 0.93) | 0.85 (0.75, 0.96) | 0.77 (0.67, 0.88) | 0.80 (0.70, 0.91) | 0.001 |
| Colon cancer | ||||||
| Men | ||||||
| No. of cases | 130 | 137 | 134 | 135 | 146 | |
| Age- and energy-adjusted | 1 | 0.86 (0.67, 1.10) | 0.79 (0.62, 1.01) | 0.72 (0.56, 0.93) | 0.70 (0.55, 0.90) | 0.002 |
| Multivariate-adjusted2 | 1 | 0.88 (0.69, 1.12) | 0.82 (0.64, 1.05) | 0.78 (0.61, 1.01) | 0.82 (0.63, 1.05) | 0.10 |
| Women | ||||||
| No. of cases | 216 | 208 | 222 | 195 | 241 | |
| Age- and energy-adjusted | 1 | 0.82 (0.67, 0.99) | 0.80 (0.66, 0.97) | 0.68 (0.56, 0.83) | 0.73 (0.61, 0.88) | <0.0001 |
| Multivariate-adjusted2 | 1 | 0.83 (0.68, 1.00) | 0.83 (0.69 1.01) | 0.73 (0.59, 0.89) | 0.81 (0.66, 0.98) | 0.007 |
| Pooled | 1 | 0.85 (0.73, 0.99) | 0.83 (0.71, 0.96) | 0.75 (0.64, 0.87) | 0.81 (0.69, 0.95) | 0.002 |
| Rectal cancer | ||||||
| Men | ||||||
| No. of cases | 45 | 38 | 54 | 41 | 40 | |
| Age- and energy-adjusted | 1 | 0.69 (0.44, 1.07) | 1.00 (0.67, 1.50) | 0.70 (0.45, 1.08) | 0.60 (0.39, 0.94) | 0.15 |
| Multivariate-adjusted2 | 1 | 0.73 (0.47, 1.13) | 1.10 (0.73, 1.66) | 0.80 (0.51, 1.25) | 0.72 (0.45, 1.15) | 0.64 |
| Women | ||||||
| No. of cases | 71 | 62 | 67 | 62 | 61 | |
| Age- and energy-adjusted | 1 | 0.76 (0.54, 1.07) | 0.79 (0.56, 1.10) | 0.70 (0.49, 0.99) | 0.61 (0.43, 0.87) | 0.02 |
| Multivariate-adjusted2 | 1 | 0.79 (0.56, 1.12) | 0.86 (0.61, 1.21) | 0.80 (0.56, 1.14) | 0.74 (0.52, 1.07) | 0.34 |
| Pooled | 1 | 0.77 (0.58, 1.00) | 0.95 (0.73, 1.24) | 0.80 (0.61, 1.06) | 0.73 (0.55, 0.98) | 0.31 |
Relative risks were computed from a Cox proportional hazards model.
Adjusted for the same covariates as in Table 3.
For proximal colon cancer, we observed an inverse association with both DASH (multivariate RR comparing highest to lowest quintiles: 0.81; 95% CI: 0.63, 1.04; P for trend = 0.02) and aMed (RR: 0.77; 95% CI: 0.59, 0.96; P for trend = 0.01) scores among women only. The aMed score was not associated with distal colon cancer, but a significant inverse association was noted for the DASH score (pooled RR when comparing top with bottom quintile: 0.76; 95% CI: 0.59, 1.01, P for trend = 0.02).
We then explored the association of each component of the DASH score and total colorectal cancer. Whole-grain intake was inversely associated with colorectal cancer in the HPFS. The RR for each serving increase was 0.94 (95% CI: 0.88, 0.99) (Table 5). On the other hand, each serving increase in sweetened beverages was associated with a 17% increase risk of colorectal cancer in men (RR: 1.17; 95% CI: 1.02, 1.33) but not in women. Among women, low-fat dairy products (RR for 1 serving increase: 0.89; 95% CI: 0.83, 0.96) and fruit (RR: 0.95; 95% CI: 0.90, 0.99) were associated with lower risk of total colorectal cancer. We then tested the contribution of each component by adding them one at a time to the regression model that contains the DASH score and found that the same components (ie, fruit and low-fat dairy for the NHS and sweetened beverages and whole grains for the HPFS) were the strongest contributors for the inverse association observed between the DASH score and colorectal cancer.
TABLE 5.
Multivariate relative risks (95% CI) for each serving/d increase in Dietary Approaches to Stop Hypertension food components for total colorectal cancer1
| Women (n = 87,312) | Men (n = 45,080) | |
| Fruit | 0.95 (0.90, 0.99) | 1.01 (0.96, 1.05) |
| Nuts | 1.02 (0.91, 1.14) | 1.04 (0.94, 1.15) |
| Vegetables | 1.01 (0.96, 1.05) | 1.00 (0.96, 1.04) |
| Red/processed meats | 1.12 (0.99, 1.26) | 1.08 (0.97, 1.21) |
| Sodium2 | 1.06 (0.93, 1.21) | 0.98 (0.90, 1.06) |
| Low-fat dairy | 0.89 (0.83, 0.96) | 0.97 (0.90, 1.04) |
| Sweetened beverages | 1.04 (0.94, 1.16) | 1.17 (1.02, 1.33) |
| Whole grains | 0.95 (0.89, 1.02) | 0.94 (0.88, 0.99) |
Values were adjusted for the same variables as in Table 3. Relative risks were computed from a Cox proportional hazards model.
Per 1000-mg increment in sodium intake.
DISCUSSION
In our 2 cohorts of US men and women with ≤20–26 y of follow-up, we observed that a higher DASH score was associated with a lower risk of colorectal cancer. In addition, the DASH score may also be associated with a lower risk of rectal cancer. We found no significant association between the aMed and colorectal, colon, or rectal cancers.
Current data on the association between the Mediterranean diet and colorectal cancer generally pointed toward a reduction of risk, but results were not overwhelmingly consistent. A meta-analysis of prospective studies documented a 6% reduction in cancer mortality for every 2-point increase in Mediterranean diet score (5). However, among members of the Prostate, Lung, Colorectal, and Ovarian Screening (PLCO) Trial, a higher Mediterranean diet score was associated with a lower prevalence of distal colorectal adenomas only in men (6). Similarly, in the NIH-AARP cohort with 5 y of follow-up, adherence to a Mediterranean diet score that was defined similarly to our score was associated with lower risk of colorectal cancer incidence only in men (RR when comparing top with bottom quintiles: 0.72) (7). In addition, significant risk reduction was also observed for distal colon and rectal cancer in men but not in women. We did not observe a sex-specific difference in risk, and our association is less strong than reported in the AARP cohort.
Data on the DASH diet and cancer outcome are sparse. In a population-based cohort of individuals with hypertension with a mean follow-up of 8.2 y, there was a suggestion of an inverse association between those who adhered to a DASH-like diet and cancer mortality (HR: 0.51, 95% CI: 0.23–1.10) (20). To our knowledge, there is only one study on specific colorectal endpoints. A higher score in a 9-point, food group–based DASH diet score was associated with a lower prevalence of distal colorectal adenoma among male participants of the PLCO Trial (6). Our analysis, which specifically focused on incident colorectal cancer, provides stronger data that suggest an inverse association between the DASH diet and risk of colorectal cancer.
Both the Mediterranean and DASH diets emphasize plant foods. However, the possibility of fiber or whole grains being the intermediate factor is uncertain, because current data are equivocal at best (2, 3). On the other hand, both diets award points for low meat consumption. As a number of studies have shown a direct association between red and processed meats and risk of colorectal cancer (4), the inverse association that we observed between the 2 diet scores and colorectal cancer may be mediated through lower red and processed meat intake. The IGF (insulin-like growth factor) axis is a potential pathway for colorectal cancer development (21). Although the association of C-peptide, a marker of insulin secretion, and risk of colorectal cancer is not completely consistent (22) but not all studies (23). Substantial evidence suggests that diabetes is a risk factor for colorectal cancer (24), and versions of the Mediterranean diet (25) and DASH diet (26) have been associated with lower risk of diabetes.
In this analysis, an inverse association with risk of colorectal cancer was observed with the DASH score but not the aMed score. Among components that differ between the DASH and aMed, low-fat dairy products, which are part of the DASH diet, were inversely associated with colorectal cancer (9). In addition, scoring for each food group in the DASH score was based on 5 points instead of 2 in the aMed score. Thus, the DASH score may have more discriminating power.
Our data suggest a potential inverse association between the DASH score and rectal cancer. Although dietary patterns similar to the DASH diet, which is characterized by higher fruit, vegetable, and whole-grain intake, have been associated with a lower risk of rectal cancer risk, the association is not consistent across populations or sex (27, 28). On the other hand, a meta-analysis has shown a positive association with meat consumption (4). Nevertheless, our results suggest that a minimally processed, plant-based diet may lower risk of rectal cancer.
Our long follow-up allowed us to detect the association between diet and slow progressing diseases such as cancer. Our comprehensive and updated information on potential confounders allowed for detailed adjustment and minimized confounding, although we could not completely rule out residual confounding. Because of the large number of cases, we were able to examine tumors at specific anatomical sites. Because lifestyle and dietary data are recorded with some degree of error, a certain amount of misclassification is unavoidable. However, we used a validated questionnaire, so we believe the amount of misclassification is small and random.
Construction of the aMed and DASH scores was based on the literature and our a priori hypotheses. However, it still involved some level of arbitrary decision in the type and number of foods to be included and assignment of points to different amounts of intake. In previous studies on cardiovascular disease, the aMed nevertheless performed similarly with other Mediterranean diet scoring algorithms (5, 29). In a previous study, the DASH score used in this study was inversely associated with cardiovascular mortality (11), which agrees with the results of the original DASH trials on blood pressure reduction (8). Therefore, we believe that our scoring algorithm is successful in capturing the important features of these 2 diets.
Adherence to the DASH diet (which involves higher intake of whole grains, fruits, and vegetables; moderate amounts of low-fat dairy; and lower amounts of red or processed meats, desserts, and sweetened beverages) was associated with a lower risk of colorectal cancer.
Acknowledgments
The authors' responsibilities were as follows—TTF and FBH: contributed to the design and analysis of the study; and all authors: were involved in the interpretation of the data and review and approval of the manuscript. TTF had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. There were no potential conflicts of interest for any of the authors.
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