Enterolactone, a
phytoestrogen belonging to the class of
lignans, is produced by the intestinal microflora from precursors in plant foods and has been implicated in protection against
cancer. We study the effect of
enterolactone on the risk of a subsequent diagnosis of
prostate cancer. We conducted a longitudinal, nested case-control study by linkage of 3 biobanks to the
cancer registries in Finland, Norway and Sweden, respectively.
Enterolactone concentrations were measured by time-resolved fluoroimmunoassay in serum from 794 men who had a diagnosis of
prostate cancer at a mean follow-up time of 14.2 years after blood collection and among 2,550 control men matched within each cohort for age (+/-2 years), date of blood collection (+/-2 months) and county. The median
enterolactone concentrations did not differ between case and control subjects in the full study group (8.4 nmol/L [25th-75th percentile = 4.5-15.0] vs. 8.5 nmol/L [25th-75th percentile = 4.3-15.9]), nor in the national groups. Odds ratios of
prostate cancer risk estimated by conditional logistic regression for increasing concentrations of
enterolactone in quartiles in the full study group were 1.00 (referent), 1.21 (95% confidence interval [CI] = 0.96-1.52), 1.16 (95% CI = 0.91-1.47) and 1.08 (95% CI = 0.83-1.39). The OR estimate for the highest vs. the lowest quartile of
enterolactone in separate analyses of the Norwegian, Finnish and Swedish cohort was 1.21 (95% CI = 0.91-1.60), 1.02 (95% CI = 0.59-1.76) and 0.87 (95% CI = 0.45-1.67), respectively. No support for the hypothesis that high circulating
enterolactone is protective against
prostate cancer was found.