I pulled out my copy of "Prescription for Nutritional Healing" by James Balch MD and Pylliss Balch CNC. A good basic book that is reconized by many health experts. It says "Unless your health care provider prescribes it, do not take more than 400 micrograms daily".
The book also gives the symptoms for excessively high selenium levels: arthritis, brittle nails, garlicky breath odor, gastrointestinal disorders, hair loss, irritability, liver and kidney impairments, a metallic taste in the mouth, pallor, skin eruptions, tooth loss, and yellowish skin.
It also states that "selenium and vitamin E act sygnergistically to aid in the production of antibodies and to help maintain a healthy heart and liver."