For 32 districts of Omsk oblast, the levels of selenium accumulation were determined across trophic levels: soil, plants, animals, and human. An inverse correlation was found between serum selenium concentration and parameters of total mortality, as well as the incidence of lung, ovarian, and rectal cancer. Significant differences were shown in the coefficient of plant selenium accumulation depending on the soil type. We discuss the most promising approaches to optimizing the selenium status of the population.