Some researchers feel that this study tested amounts of beta-carotene that were too little and given too late. They believe that there are still plenty of good reasons to get enough of this nutrient, Dr. Menzel says. Most experts recommend getting beta-carotene from foods rather than supplements, as foods contain many other substances that may also be important for cancer prevention. Dr. Menzel suggests that people get about 25,000 international units of beta-carotene a day from foods or supplements. Some doctors also recommend taking the Daily Value of vitamin A , which is 5,000 international units.
Medical researchers round out their antipollution prescriptions with the mineral selenium .
Doctors recommend getting from 50 to 200 micrograms of selenium daily from foods and supplements. Studies show that most people get about 108 micrograms a day from foods. So it's probably not necessary to take a supplement. If you do take a supplement, don't exceed 100 micrograms daily without medical supervision. In high amounts, selenium can be toxic.