Selenium

  • Essential for proper functioning of the antioxidant enzyme glutathione peroxidase, which protects red blood and other cells against free radical damage. Selenium is a constituent part of up to 100 selenoproteins that may exist in mammalian systems. Some 25 of them have been partially or fully characterized (1).
  • Required for the proper thyroid hormone synthesis, activation and metabolism (2,3). In humans, the thyroid gland has the highest selenium content per gram of tissue of all other organs.
  • Exerts multiple actions on the endocrine system by modifying the expression of some 30 selenoproteins such as glutathione peroxidases, thioredoxin reductases and deiodinases. These groups of enzymes act as antioxidants, control the cellular redox status and modulate thyroid hormone (triiodothyronine) metabolism, respectively. Selenium was also found to stimulate the tyrosine kinases involved in the insulin signalling cascade. In this respect selenium exhibits insulin-like properties (4).
  • Involved in cell growth, apoptosis and modifying the action of cell signalling systems and transcription factors.
  • Selenium has a modulatory effect on the immune system (5).
  • Interactions: Selenium absorption is adversely affected by heavy metals, such as lead and mercury. High zinc intake may decrease selenium absorption.
  • Health benefits: Marginal selenium deficiency in humans may contribute to reduced immune function, some cancers and viral diseases (6). Animal model experiments indicated that selenium supplementation was associated with increases in natural killer cell activity, T cell proliferation, lymphokine- activated killer cell activity. In humans, selenium supplementation led to augmented cellular response through an increased production of interferon gamma and other cytokines, increased number of T helper cells in subjects challenged with attenuated live poliomyelitis vaccine (7). Supplementation was also found useful in patients with systemic inflammatory response syndrome and sepsis (8). Supplementation may also help prevent cardiovascular disease and cancer as well as inflammatory conditions, such as rheumatoid arthritis.
  • Best food sources: Wheat germ, nuts, bran, garlic, whole grains. The concentration of selenium in the food is related to the level of the mineral in soil.


References
1. Burk, R.F. & Hill, K.E. (1993) Annu.Rev.Nutr. 13, 65-81. Regulation of selenoproteins.
2. Kohrle, J. (1999) Biochimie 81(5) 527-533. The trace element selenium and the thyroid gland.
3. Kohrle, J. (2005) Thyroid 15(8) 841-853. Selenium and the control of thyroid hormone metabolism.
4. Beckett, G.J. & Arthur, J.R. (2005) J.Endocrinol. 184(3) 455-465. Selenium and endocrine systems.
5. Ferencik, M. & Ebringer, L. (2003) Folia Microbiol.(Praha) 48(3) 417-426. Modulatory effects of selenium and zinc on the
    immune system.
6. Rayman, M.P. (1997) Brit.Med.J. 314, 387-388. Dietary selenium:time to act.
7. Broome, C.S. et al. (2004) Am.J.Clin.Nutr. 80(1) 154-162. An increase in selenium intake improves immune function and
    poliovirus handling in adults with marginal selenium status.
8. Gartner, R. et al. (2001) Biofactors 14(1-4) 199-204. The effect of a selenium supplementation on the outcome of patients
    with severe systemic inflammation, burn and trauma.