Whole grain and dietary fiber intake and risk of colorectal cancer in the NIH-AARP Diet and Health Study cohort

Supported in part by the Intramural Research Program of the National Cancer Institute at the NIH. Supplemental Tables 1–5, Supplemental Figure 1, and Supplemental Methods are available from the “Supplementary data” link in the online posting of the article and from the same link in the online table of contents at https://academic.oup.com/ajcn/. The data sets analyzed for this study were obtained from the National Cancer Institute. Researchers can request access to the data from the NIH-AARP Diet and Health Study online at https://dietandhealth.cancer.gov/. Analytic code can be obtained from the corresponding author upon request.
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ABSTRACT

Background

Whole grains and other foods containing fiber are thought to be inversely related to colorectal cancer (CRC). However, whether these associations reflect fiber or fiber source remains unclear.

Objectives

We evaluated associations of whole grain and dietary fiber intake with CRC risk in the large NIH-AARP Diet and Health Study.

Methods

We used Cox proportional hazard models to estimate HRs and 95% CIs for whole grain and dietary fiber intake and risk of CRC among 478,994 US adults, aged 50–71 y. Diet was assessed using a self-administered FFQ at baseline in 1995–1996, and 10,200 incident CRC cases occurred over 16 y and 6,464,527 person-years of follow-up. We used 24-h dietary recall data, collected on a subset of participants, to evaluate the impact of measurement error on risk estimates.

Results

After multivariable adjustment for potential confounders, including folate, we observed an inverse association for intake of whole grains (HRQ5 vs.Q1 : 0.84; 95% CI: 0.79, 0.90; P-trend < 0.001), but not dietary fiber (HRQ5 vs. Q1: 0.96; 95% CI: 0.88, 1.04; P-trend = 0.40), with CRC incidence. Intake of whole grains was inversely associated with all CRC cancer subsites, particularly rectal cancer (HRQ5 vs. Q1: 0.76; 95% CI: 0.67, 0.87; P-trend < 0.001). Fiber from grains, but not other sources, was associated with lower incidence of CRC (HRQ5 vs. Q1: 0.89; 95% CI: 0.83, 0.96; P-trend < 0.001), particularly distal colon (HRQ5 vs. Q1: 0.84; 95% CI: 0.73, 0.96; P-trend = 0.005) and rectal cancer (HRQ5 vs. Q1: 0.77; 95% CI: 0.66, 0.88; P-trend < 0.001).

Conclusions

Dietary guidance for CRC prevention should focus on intake of whole grains as a source of fiber.

Keywords:

colorectal cancer
whole grains
dietary fiber
colon cancer
rectal cancer
diet
epidemiology

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