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It has been a while since I started this series. I am sorry for taking so long before writing the next episode. I want to thank everyone who upvoted the last part and I hope you like this one too.

Pure selenium in the periodic table of my faculty

Depending of the support I receive I will continue this series with more or less posts.

Selenium health effects

It is important to remember from the last episode that selenium is an essential element for animals, including humans.

Selenium is part of some proteins. Selenoproteins are those proteins that requires selenium for working properly. They have selenocysteine (SeCys), the so-called 21st amino-acid, in their sequence. They have specific functions like contributing to the immunity system, muscle metabolism, reducing oxidation damage and other things. They help making some essential chemical reactions much faster, acting like catalyst.

Proteins containing selenium are those that have methionine amino-acid replaced by selenomethionine in random positions. Those proteins can properly work without selenium, but that element protects them from oxidation damage. They also act as selenium reserve, because selenomethionine can be converted into selenocysteine when required.

An excess of selenium can be dangerous. In soils with high concentrations of selenium, beasts can lose their hooves after stepping on plants accumulating selenium. This element was discovered after investigating illness of workers in a factory using pyrites. The selenium contained in this sulphur mineral was the cause of that illness. An excess intake of selenium through diet can also be toxic, consuming antioxidant molecules.

On the other hand, there are some muscle and heart diseases linked with selenium deficit. In 1957, Schwarz and Foltz found that rats that receive a diet depleted in selenium suffered hepatic necrosis, and that disease could disappear after providing them a diet rich in selenium.

The first two diseases in humans caused by selenium deficit were discovered in regions of the North of China, North Korea and Eastern Siberia. The Kashin–Beck disease is a deforming arthritis caused by lack of antioxidant selenium enzymes and leads to deformation of bone structure. The Keshan disease is an endemic cardiopathy associated with the degeneration of organ and tissues.

Recent studies have reported that selenium has positive health effects at decreasing cardiovascular disease mortality, maintaining bone homeostasis and preventing some forms of cancer[1]

Selenium is obtained by animals from the diet. Plants take up an assimilate selenium from soil because its similarity to sulphur, however it has not been proved it is essential for this organisms. Plants transform inorganic species present in soil into organic forms, that are more suitable for animals.

Optimal intake

The safe intake range of selenium for humans is narrow compared to other nutrients, between 50 and 400 micrograms per day, and the optimal intake range is 55-70 ug/day. An optimum intake of selenium not only prevents toxicity and deficit illness but also reduces hearts diseases, prevents cancer, and decreases oxidation damage, among other benefits. Values have small variation depending of age, sex, and the nutrition agency that issues the recommendation.

Dietary Reference Values for selenium for adults[2]

In conclusion, selenium intake has an important impact in human health, and it is important to maintain the intake in a narrow range for obtaining their health benefits.

In next chapters

• Food with selenium
• How selenium in food is analyzed
• Selenium amount in fish
• Conclusions

Thanks for your attention. I will be glad to explain any question about this topic.

Bibliography

[1] Brozmanová, J., Mániková, D., Vlčková, V., & Chovanec, M. (2010). Selenium: a double-edged sword for defense and offence in cancer. Archives of Toxicology, 84(12), 919–938. https://doi.org/10.1007/s00204-010-0595-8
[2] EFSA. (2014). Scientific opinion on dietary reference values for selenium. European Food Safety Authority Journal, 12(10), 67. https://doi.org/10.2903/j.efsa.2014.3846