CHAPTER 22: Selenium and Cancer

Selenium is a trace element that is an essential component of many enzymes that play an important role in several major metabolic pathways and ameliorate environmental insult, including the antioxidant defense system, the immune system and functioning of the thyroid gland. There is a range of serum selenium levels associated, with the lowest rate of all causing mortality – the levels should be maintained at an optimal level and be neither too low nor too high. Selenium intake varies, largely based on the selenium content of food. The mean level of selenium in the population varies considerably between countries. Thus, for some countries selenium supplementation should be considered, whereas for others it could be contraindicated. Recent meta-analyses indicate unequivocally that selenium supplementation of people with low initial serum selenium levels decreases the incidence of cancer incidence by ∼35% and of cancer mortality by almost 50%. Additionally, it appears that in Se-deficient countries selenium levels may be a useful marker to select patients for cancer surveillance using for example computerized tomography for detection of the earliest stages of bronchial malignancy and colonoscopy for detection of the early stage colorectal cancer.