Prevention of Female Cancers by Optimization of Selenium Levels in the Organism.

Primary Objective • To determine the efficacy of oral daily supplementation or diet modification of selenium to an optimal level compared to placebo, in reducing the incidence of any cancers in an at risk population of women over the 60 months of the study. Secondary Objectives * To determine the efficacy of oral daily supplementation or diet modification of selenium to an optimal level compared to placebo, in reducing the incidence of breast cancer in an at risk population of women over the 60 months of the study. * To explore the relationship between the effects of study supplement or diet modifications on cancer risk and genetic factors. The study will have 7000 participants. All the measurements will be performed via blood tests.