Selenium also helps detoxify some of the toxic heavy metals in cigarette smoke, such as mercury and cadmium. A study led by Dr. Walter Willett of the Harvard School of Public Health found that people who came down with certain types of cancer had low selenium blood levels several years prior to the discovery of their cancers. Dr. Gerald Schrauzer, a long-time selenium researcher at the University of California in San Diego, believes that the evidence that selenium can help protect against cancer is strong enough to suggest that virtually everyone should be sure they are receiving adequate amounts of this mineral. Selenium content of vegetables may vary over 100-fold depending on the region in which they were grown. Selenium supplements are available in both inorganic and organic forms.
Some researchers believe that the organic forms have fewer toxic effects.
Selenium toxicity can occur if doses larger than 200 micrograms per day are taken regularly. Symptoms of selenium toxicicy include fragile or darkened fingernails, a metallic taste in the mouth, a metallic or garlicky smell to the breath, nausea, and dizziness. It is extremely unlikely that selenium could completely reverse the harmful effects of tobacco smoke. This vitamin helps detoxify the cyanide found in tobacco smoke. Smokers excrete more B-12 and thus have lower serum levels.