It is suspected that selenium is protective against prostate cancer, To tes
t this hypothesis, we conducted a nested case-control study in a cohort of
9345 Japanese-American men examined between 1971 and 1977, At the time of e
xamination, a blood specimen was obtained, and the serum was frozen, After
a surveillance period of more than 20 years, 249 tissue-confirmed incident
cases of prostate cancer were identified. Their stored sera and those of 24
9 matched controls were measured for selenium levels. Odds ratios for prost
ate cancer, based on quartiles of serum selenium levels, were determined us
ing the General Estimating Equations approach, The multivariate odds ratio
for the highest quartile was 0.5 (95% confidence interval, 0.3-0.9) with a
two-sided P for trend of 0.02, The inverse association was more notable for
cases with advanced disease and for cases diagnosed 5-15 years after phleb
otomy, However, the association was mainly present in current or past cigar
ette smokers rather than nonsmokers, which leads to caution in the interpre
tation of the results.