Abstract: The present invention solves the need for non-toxic forms of selenium which is an essential part of the human diet. This invention provides novel dried-yeast products containing selenium as well as a method of producing the dried yeast products. The method uses selenium having high biological activity but low toxicity. The invention also provides nutritional supplements containing the novel selenium containing dried yeast products and methods of administering these products and supplements to improve human health. The invention also provides a practically non-toxic yeast selenium product having increased intracellular selenium concentrations and methods to reduce tumor cell growth by administration of a selenium yeast product comprising yeast Saccharomyces boulardii sequela PY 31 (ATCC 74366) in combination with chemotherapeutic agents.