290
Trace Elements in Abiotic and Biotic Environments
Blood Se levels are inversely associated with the prevalence of several types of
cancer. Reduced cancer risk is associated with Se treatment, although the Se supplementation was not related to reduce in prostate cancer risk.
Very low dietary intakes of Se by humans have been associated with incidence of Keshan and Kashin–Beck diseases. Keshan disease is a cardiomyopathy
that affects young women and children in the Se-deficient region of China. The
acute form of the disease is characterized by the sudden onset of cardiac insufficiency, while the chronic form results in moderate to severe heart enlargement,
with varying degrees of cardiac insufficiency. Kashin–Beck disease is characterized by the degeneration of articular cartilage between joints (osteoarthritis)
and is associated with poor Se status in areas of northern China, North Korea,
and eastern Siberia. The disease affects children between the ages 5 and 13 years
(WHO 2004).
At low Se levels in persons virulence in viral pathogens may decrease. A decline
in Se status in humans with immunodeficiency virus (HIV) has been observed.
There is an evidence that Se supplementation can have a beneficial effect on HIV
and AIDS patients (Reilly 2002).
High dietary intakes of Se have been identified in parts of Venezuela, China, and
South Dakota (the United States). Excessive Se intakes can lead to chronic toxicity
(selenosis), with health damages, such as loss of hair and nails, skin lesions, hepatomegaly, polyneuritis, and gastrointestinal disturbances. Different chemical forms of
Se can have vastly different toxic potentials, and for elemental Se seems to be less
toxic.
Occupational exposure to Se usually occurs through direct contact and/or through
inhalation. Exposure to Se and its compounds occurs in both Se industries, primary
and secondary. For acute occupational Se exposures, the effects vary according to
the chemical form of Se, of which the elemental Se appears to be nontoxic.
Various national and international organizations have established recommended
daily intakes of Se. A joint Food and Agriculture Organization (FAO)/WHO consultation recommended its intake of 6–21 μg/day for infants and children, according
to age, and 26 and 35 μg/day for adult females and males, respectively. Because of
concern about the adverse effects resulting from exposure to excessive levels of Se,
various national and international organizations have established upper limits
of exposure for Se. The FAO/WHO established an upper tolerable limit for Se of
400 μg/day (WHO 2011e).
In plant and animal tissues, Se is found mostly bound to proteins. Therefore, the
most important food sources of Se are meats and seafood, because of their high
protein contents; and cereals, due to their large consumption. Foods with relatively
low protein levels, such as vegetables and fruits, have relatively low Se contents
(Table  42.2). Global Se intakes vary significantly in the range from about 0.03
to 0.5 mg/day. Its average dietary intakes in various countries are as follows (in
mg/day): Europe, 0.04–0.09; China, 0.01–0.20; and  Switzerland, 0.066. In most
countries, Se intake is estimated at the level of 0.06/day (Jenny-Burri et al. 2010).
In the United Kingdom, the miscellaneous cereals (in 16%) and the meat products
group (in 15%) made the greatest Se contribution to the population dietary exposure (Rose et  al. 2010). In Switzerland, pasta made of North American durum