Plasma alkylresorcinol metabolites as biomarkers for whole-grain intake and their association with prostate cancer: a Swedish nested case-control study.

BACKGROUND:Observational studies have mostly found no association between self-reported whole-grain intake and prostate cancer. Plasma alkylresorcinol metabolites have been suggested as biomarkers for whole-grain intake in free-living populations. METHODS:We investigated the major dietary and lifestyle determinants of plasma alkylresorcinol metabolites in a nested case-control study (1,016 cases and 1,817 controls) in the Malmö Diet and Cancer Study. Multivariate adjusted ORs and 95% confidence intervals (95% CI) were estimated to assess the association between plasma alkylresorcinol metabolites and prostate cancer using logistic regression. RESULTS:Whole-grain intake, waist circumference, educational level, and smoking status were the main determinants of alkylresorcinol metabolites. We observed significant correlations between alkylresorcinol metabolites and whole-grain (r = 0.31) and fiber (r = 0.27) intake. Metabolite concentration was positively associated with prostate cancer risk (Poverall effect = 0.0004) but the association was not linear (P = 0.04). The lowest risk was seen among men with moderate plasma concentrations. The OR for high compared with moderate plasma alkylresorcinol metabolites was 1.41 (95% CI, 1.10-1.80) for prostate cancer. CONCLUSIONS:Results suggest that plasma alkylresorcinol metabolites are mainly determined by whole-grain intake in this nested case-control study of Swedish men. The increased risk of prostate cancer seen among men with high plasma alkylresorcinol metabolites requires further study, but residual confounding, detection bias, or competing risks of nonprostate cancer-related deaths are plausible explanations that could not be ruled out. IMPACT:We found no evidence of a protective effect of whole grains on incident prostate cancer. Further validation of alkylresorcinol metabolites as a biomarker for whole-grain intake is needed.