Abstract
ABSTRACTBackgroundHigher intakes of whole grains and dietary fiber have been associated with lower risk of insulin resistance, hyperinsulinemia, and inflammation, which are known predisposing factors for cancer.ObjectivesBecause the evidence of association with bladder cancer (BC) is limited, we aimed to assess associations with BC risk for intakes of whole grains, refined grains, and dietary fiber.MethodsWe pooled individual data from 574,726 participants in 13 cohort studies, 3214 of whom developed incident BC. HRs, with corresponding 95% CIs, were estimated using Cox regression models stratified on cohort. Dose–response relations were examined using fractional polynomial regression models.ResultsWe found that higher intake of total whole grain was associated with lower risk of BC (comparing highest with lowest intake tertile: HR: 0.87; 95% CI: 0.77, 0.98; HR per 1-SD increment: 0.95; 95% CI: 0.91, 0.99; P for trend: 0.023). No association was observed for intake of total refined grain. Intake of total dietary fiber was also inversely associated with BC risk (comparing highest with lowest intake tertile: HR: 0.86; 95% CI: 0.76, 0.98; HR per 1-SD increment: 0.91; 95% CI: 0.82, 0.98; P for trend: 0.021). In addition, dose–response analyses gave estimated HRs of 0.97 (95% CI: 0.95, 0.99) for intake of total whole grain and 0.96 (95% CI: 0.94, 0.98) for intake of total dietary fiber per 5-g daily increment. When considered jointly, highest intake of whole grains with the highest intake of dietary fiber showed 28% reduced risk (95% CI: 0.54, 0.93; P for trend: 0.031) of BC compared with the lowest intakes, suggesting potential synergism.ConclusionsHigher intakes of total whole grain and total dietary fiber are associated with reduced risk of BC individually and jointly. Further studies are needed to clarify the underlying mechanisms for these findings.
Highlights
Bladder cancer (BC) is the 10th most common malignancy worldwide, with an estimated 550,000 new cases and 200,000 deaths annually [1, 2]
This large, multicenter, prospective cohort study indicates a potential beneficial effect of total whole grain and total dietary fiber intake for the prevention of bladder cancer (BC), whereas intakes of total refined grain and individual fiber sources did not show any significant association with BC risk. This is the first prospective study to investigate the association between whole grain intake and BC risk; in line with this result a previously conducted casecontrol study reported a nonsignificant protective effect of higher intake of total whole grains on BC risk [23], and another casecontrol study conducted in the 1980s reported a modest inverse association [24]
Because it was reported that an increased BC risk was associated with a high dietary glycemic load [23], which has been reported to be reduced by the postprandial glucose and insulin responses to whole grain intake [61], the authors suggested that any potential benefit of whole grain intake to BC risk may act by mitigating the carcinogenic effects of hyperglycemia and hyperinsulinemia [62,63,64]
Summary
Bladder cancer (BC) is the 10th most common malignancy worldwide, with an estimated 550,000 new cases and 200,000 deaths annually [1, 2]. During the refining process, the outer bran and inner germ are removed and only the endosperm is retained This results in a substantial reduction in dietary fiber, vitamins, minerals, and other components. Results: We found that higher intake of total whole grain was associated with lower risk of BC (comparing highest with lowest intake tertile: HR: 0.87; 95% CI: 0.77, 0.98; HR per 1-SD increment: 0.95; 95% CI: 0.91, 0.99; P for trend: 0.023). Intake of total dietary fiber was inversely associated with BC risk (comparing highest with lowest intake tertile: HR: 0.86; 95% CI: 0.76, 0.98; HR per 1-SD increment: 0.91; 95% CI: 0.82, 0.98; P for trend: 0.021). Conclusions: Higher intakes of total whole grain and total dietary fiber are associated with reduced risk of BC individually and jointly
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