Cancer. Selenium has anticancer properties, possibly through its effects on the immune system or its antioxidant actions (Fig. 3.16). Regions of the USA with the highest intakes of selenium tend to have lower rates of cancer,8,9 and higher blood levels of selenium are associated with lower risk of cancer.8,9 Supplementation in older men can reduce risk of lung, colon, and prostate cancer by nearly 50%.9
Fig. 3.16: Role of selenium in primary prevention of cancer. In an intervention trial including nearly30000 adults, 7500 received an antioxidant supplement con taining 50|ig selenium (along with 30 mg vitamin E and 15 mg beta-carotene) for 5 years. The supplemented group had a significant 13% reduction in cancer mortality, compared with those not receiving the supplement. (Adapted from Blot WJ, etal. J Nat Cancer Inst. 1993;85:148)
Chronic inflammatory disorders. Diseases such as rheumatoid arthritis7 and inflammatory bowel disease may benefit from increased intake of selenium.
Infectious disease. Selenium deficiency appears to increase susceptibility to, and severity of, viral infections.3,4 Selenium deficiency is associated with a sharply higher risk of mortality from AIDS.10
Heart disease. Severe selenium deficiency, possibly exacerbated by concomitant vitamin E deficiency and viral infection, produces cardiomyopathy and heart failure (Keshan disease).16 This disorder is found mainly in adolescents and young women. Decreased selenium levels in blood have been found in patients with coronary heart disease.11 In heart disease patients, particularly those with low selenium intakes, increasing selenium intake may be beneficial.
Hypothyroidism. Selenium deficiency may reduce peripheral activation of thyroid hormones and may trigger or exacerbate hypothyroidism.5
Childhood osteoarthritis. Severe selenium deficiency may contribute to cases of juvenile osteoarthritis (Kashin-Beck disease).1,6
Heavy body burden of heavy metals. Selenium may help prevent chronic accumulation of lead and mercury from environmental contamination of the food and water supply.
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