Dietary deficiency in selenium has been associated with a wide range of conditions, from the development of cardiomyopathy involved in Keshan disease to mood disorders and Parkinson's disease.25 28 Considering the role of selenium in anti-oxidant enzymes such as GPx, it is not surprising that selenium deficiency is implicated in conditions associated with oxidative stress, such as atherosclerosis.23,26,27,29 Selenium dietary supplements, sodium selenite and selenium-enriched yeast are available to counter potential deficiency and a number of excellent reviews address the consequences of inadequate selenium intake.26,27,30 Whilst both sodium selenite and selenomethionine (SeMet) (present in Se-rich yeast) are available for biosynthesis of selenoproteins, SeMet is advocated by some as a preferred source of selenium as it is the form commonly found in food and is less toxic than sodium selenite.26,31 Excess SeMet can be stored in non-specific body proteins in place of methionine; thus SeMet appears to increase selenium levels more efficiently than sodium selenite (Figure 17.1). However, selenium from SeMet is less bioavailable and SeMet stored in proteins must undergo a longer metabolic pathway to generate H2Se for use in selenoprotein synthesis than sodium selenite.26,31
A symptom of asthma is lung inflammation, which has been associated with the generation of hydrogen peroxide as a by-product of increased metabolic activ-ity.32 Hydrogen peroxide activates a nuclear transcription factor for inflammatory cytokines, NF-kB.32,33 GPx appears to have a role in the regulation of NF-kB activity. Comparison of selenium-deficient and selenium-supplemented cells showed upregulation and inhibition of NF-kB, respectively. Whether these results are purely due to removal of hydrogen peroxide by GPx remains unclear.17 Studies have found evidence of a relationship between dietary selenium intake and asthma, and subjects supplemented with dietary sodium selenite showed decrease in asthma symptoms.26 Recent research by Kim and co-workers established that GPx levels increased and the activity of NF-kB was reduced in allergen-sensitized mice treated with sodium selenite. Additionally, selenium-pretreated mice were less affected by exposure to the allergen.32
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.