Skip to main content

Selenium is essential but we don’t get enough from fish and shellfish

Selenium is essential but we don’t get enough from fish and shellfishSelenium is crucial for your thyroid function, immune system, cardiovascular system, and even for preventing cancer. Fish and shellfish are among the best selenium sources, but even 200 grams of fish and shellfish five days a week won’t do the trick, according to a Danish selenium study. What makes it even more difficult to obtain optimal amounts of this nutrient is that the agricultural soil in large parts of Europe is stripped of vital nutrients like selenium. Margaret P. Rayman, one of Europe’s leading experts on selenium, says that there is a direct link between the decreasing selenium intake and the increasing rate of cancers, rheumatism, infertility, and numerous other health problems. The question is, how do we humans get enough selenium?

Danish researchers set up a project, in which 60 men and women volunteered to eat, as part of their daily diet, 200 grams of fish and shellfish five days a week for a period of six months. The scientists wanted to see specifically how selenium intake affected the health of the study participants. The study also included a control group, whose participants were instructed to continue eating their normal diet and make a note if they consumed any fish or shellfish.
What got the researchers interested in selenium was some American studies that revealed selenium’s multiple health benefits and addressed the issue that Americans generally get more selenium from the diet, simply because the agricultural soil and, hence, the crops that grow in the soil contain higher levels of the nutrient.

Not enough selenium from the Danish fish diet

Selenium is a part of around 30 different selenoproteins that have different functions in the body. In the Danish seafood study, the scientists looked specifically at whether daily consumption of fish and shellfish was able to saturate the selenium-dependent protein, selenoprotein P, which is responsible for transporting selenium to different tissues, and which is an excellent biological marker of blood selenium levels.
Studies show that it takes around 100 micrograms of selenium daily for optimal saturation of selenoprotein P. However, even with the 200 grams of fish and shellfish consumed by the volunteers in the Danish study, it was not possible to reach the saturation level.

Mercury increases the need for selenium

Other factors limited their selenium status in this study. Fish and shellfish contain heavy metals such as mercury, and because selenium atoms bind to mercury and neutralize the toxin by means of a chemical process, these selenium atoms are no longer available to the more than 30 selenoproteins that need selenium for proper functioning. In other words, the body is unable to absorb and utilize selenium from fish and shellfish if the selenium has already formed a chemical bond with mercury. Therefore, mercury increases the need for selenium.

Supplements may be a solution

The selenium we get from plants and animals is always organic, while the selenium that is found in supplements can be either organic or inorganic. Studies reveal that the body absorbs, utilizes, and stores organic selenium substantially better than inorganic selenium. This is of vital importance, as selenium is involved in so many biochemical processes.
Selenium supplements based on organic selenium yeast contain a variety of selenium compounds and provide the same variety of selenium species that you get from eating a balanced diet with several good selenium sources. In a Danish study where the study participants received 100 micrograms of selenium yeast daily, blood selenium levels rose to 165 ng/ml, which is considered optimal.

Selenium levels and mortality

  • Serum selenium levels:
  • Below 105 ng/ml = increased mortality
  • 105-170 ng/ml = mortality below average
  • 130-150 ng/ml = lowest mortality
  • The average serum selenium level in EU is around 80-100 ng/ml, which increases the risk of premature death.

Source: Margaret P. Rayman. Selenium and human health. The Lancet 2012

Table of various selenium compounds and their function

Selenium supports over 30 different selenium-dependent proteins (selenoproteins) and other selenium compounds that are of vital importance to our thyroid function, cardiovascular system, cancer preventative mechanisms, immune system, fertility, detoxification and many other functions. Even minor selenium deficiencies may result in malfunctioning of several selenoproteins.
Selenium compound Function
Deiodinase type 1-3 Thyroid hormones. Conversion of T4 to T3
(Glutathione Peroxidase) 1-6
Important antioxidants that protect cells and specific tissues. Counteract inflammation.
Methylselenol Regulation of NKG2D ligands and immune defense, which is overactive with many forms of cancer.
Selenide Binds to mercury by forming mercury selenide, a chemically inert compound. Non-organic
Selenoprotein P Transportation of selenium in the body. Important antioxidant. Controls apoptosis and DNA repair. Useful marker for measuring selenium status.
Selenoprotein T A part of cellular structures and proteins
Selenoprotein R Antioxidant. Binds zinc.
Selenoprotein N1 Antioxidant. Believed to be necessary for muscle tissue
Selenoprotein W Involved in muscular and cardiac metabolism
Thioredoxin reductase 1-3 Important for Q10’s function in cellular energy metabolism inside the mitochondria (powerhouses) of cells.


Lutz Shomburg. Dietary Selenium and Human Health. Nutrients 2017

Drutel, A et al: Selenium and the thyroid gland: more good news for clinicians. Clinical Endocrinology (2013) 78 155-164

Int J Cardiol. 2012, May 22

Margaret P. Rayman. Selenium and human health. The Lancet 2012

  • Created on .