I buy for my mother, who can not give ordinary multivitamins because of her bad habit - smoking (in a multi usually put a lot of vitamin A, which is harmful for smokers, even if the former). Normal adult for selenium - 200 micrograms. Better food and apart from zinc (they are antagonists). The first month of drink tablet every day, and the second can be - in a day. Up to six months without a break. Selenodefitsit compensated for a month and then after the cancellation can not fall another 2-3 months, while the average - selenium level falls one month after the person has finished his drink. Selena in our region, the soil contains a very small, so that would not hurt - we drink it constantly. As soon as we reduce the dosage - hello colds (I drink it as part of a multivitamin, but at the same dose). Improving digestion takes place at a joint reception with vitamin E (you can even add Ku10)