Decreased Incidence of Prostate Cancer With
Supplementation: Results of a double-blind cancer prevention trial.
July 21, 1998
A study recently published in the British Journal of Urology (1998:81;730-734) examined the relationship between dietary selenium and the incidence of prostate cancer. The study, led by Dr. Larry Clark of the Arizona Cancer Center of the College of Medicine at the University of Arizona, was conducted at several U. S. clinical centers.
A total of 974 men were randomized to either a daily dietary supplement of 200 micrograms of selenium (supplied as a half-gram high selenium yeast tablet) or a placebo. Patients were treated for a mean of 4.5 years and followed for a mean of 6.5 years. Even though the first participants entered the study in 1983, before PSA measurements were routinely available, frozen blood samples taken upon entry into the study were used to determine PSA values for most participants. The PSA values stratification by the initial PSA level, eliminating the possibility of a favorable distribution of patients with elevated PSA levels (i. e. prevalent prostate cancer cases) for the treatment group.
The selenium supplements were associated with a significant 63% reduction in prostate cancer incidence. There were 13 prostate cancer cases in the placebo group (relative risk, RR=0.37, P=0.0002). Restricting the analysis to the 843 patients with normal initial PSA levels, only four cases were diagnosed in the selenium-supplemented group and 16 cases diagnosed in the placebo group after a two-year treatment lag (RR=0.26 P=0.009). The incidence of several other cancers were also significantly decreased.