Selenium: An Essential Trace Element

We humans need an adequate dietary supply of selenium. Like iron and iodine, our bodies need this essential trace element in sufficient amounts from food for normal physiological functioning.

Prof Jan Alexander, selenium expert
Guest author Prof. Jan Alexander, MD PhD, specialist in occupational medicine, professor and former specialist director at the Norwegian Institute of Public Health, Oslo, Norway.

The content of selenium in food varies according to the selenium content of the soil in any particular region [Stoffaneller & Morse 2015]. Unfortunately, in most areas of the Nordic and Baltic countries, the soil is poor in selenium. Accordingly, the local crops and fruits tend to have low selenium content. An exception is Finland, which enriches soil fertilizers with selenium. Import of wheat from regions with high contents of selenium in the soil has earlier been an important source of selenium in Norway [Alexander & Olsen 2023].

Note: It is not possible for all selenium-poor regions of the world to adopt the Finnish model of selenium fertilization. Industrial demands for selenium are so great that not enough is available to allow for widespread fertilization with selenium. Supplementation seems to be the more economical alternative [Haug 2007].

Selenium for the Bio-Synthesis of Selenoproteins

We need adequate intakes of selenium for the synthesis and maintenance of 25 known selenoproteins. We absorb the selenium in food and supplements at a rate of approximately 70-80%. The absorbed selenium does not circulate in its elemental form; instead, it is incorporated into proteins as selenocysteine, the 21st amino acid. The selenium in the selenium-dependent selenoproteins exists in the form of selenocysteine [Alexander & Olsen 2023].

Several of these selenoproteins have important antioxidant properties. Some purpose-specific selenoproteins are also involved in the regulation of the thyroid hormones [Alexander & Olsen 2023].

Importance of Selenoprotein P

The selenoprotein known as Selenoprotein P (SELENOP) is the main transporter of selenium in the blood circulation. It plays a central role in the transport of selenium to extrahepatic tissues. SELENOP is synthesized primarily in the liver. It seems to control whole-body selenium homeostasis [Alexander & Olsen 2023].

Selenium supplementation studies show that SELENOP concentrations increase in plasma until the plasma SELENOP concentration plateaus. Thereafter, even if the selenium intake and the selenium status in plasma increase, the SELENOP level in plasma stays constant. That is to say, additional selenium intake in selenium-replete individuals does not result in an increase in SELENOP concentrations [Alexander & Olsen 2023].

Several factors affect the amount of time required for SELENOP to reach a saturation level. Among these factors are the individual’s baseline selenium status and the selenium species and dose used in the supplement. In studies, the amount of time needed to reach a saturation level of SELENOP has varied from four weeks to 30–40 weeks [Alexander & Olsen 2023].

The maximal expression of SELENOP occurs when the plasma or serum selenium concentration of selenium reaches about 110 mcg/L. Plasma and serum selenium values are equivalent [Alexander & Olsen 2023].

Thus, it can be seen that the SELENOP concentration in plasma is the most appropriate biomarker of the selenium status of the body’s regulated selenium pool. Measurements of selenium concentrations in plasma or serum are an indicator of dietary selenium intake. SELENOP status in the blood gives the best picture of overall selenium status [Alexander & Olsen 2023].

Importance of Other Selenoproteins

There is insufficient space here to enumerate the biological functions of all the selenoproteins. For a more detailed discussion, please see the review article Selenium – a scoping review for the Nordic Nutrition Recommendations 2023 by Jan Alexander and Ann-Karin Olsen.

Glutathione peroxidases

Some of the most important selenoproteins are enzymes that neutralize peroxides and protect against oxidative damage. These antioxidant seleno-enzymes include five glutathione peroxidases (GPXs) that convert hydroperoxides and lipoperoxides to water or alcohols in various body compartments [Alexander & Olsen 2023].

Thioredoxin reductases

Three thioredoxin reductases (TXNRDs) play key roles in cellular redox regulation, again in various body compartments [Alexander & Olsen 2023].

Iodothyronine deiodinases

Three deiodinase enzymes regulate thyroid hormone activity. The iodothyronine deiodinases (DIO1, DIO2, DIO3) control the central and
peripheral activation and inactivation of thyroid hormones [Alexander & Olsen 2023]. Proper thyroid activity is important for the regulation of our body’s metabolism: how efficiently we convert food into energy, how fast or slowly our heart beats, how much we gain or lose weight, and so on.

Selenium Intake Levels

Whenever supplementation is used to increase selenium intakes, the form of the selenium compound – whether inorganic or organic, whether pure selenomethionine or a selenium-enriched yeast formation – will influence the extent of the rise in plasma selenium concentration. In Finland, an estimated daily selenium intake of 88 mcg for men and 68 mcg for women has yielded plasma selenium concentrations of approximately 110 mcg/L on average [Alexander & Olsen 2023].

Note that, whereas the serum selenium concentrations in US citizens are estimated to be about 120 mcg/L on average, the mean concentrations in many northern European countries are below 90 mcg/L [Alehagen 2020].

Data from a 2022 report show the following daily adult intakes of selenium in Nordic countries [Lemming & Pitsi 2022].

  • Denmark: 61 mcg (men) and 46 mcg (women)
  • Finland 88 mcg (men) and 68 (women)
  • Sweden 50 mcg (men) and 42 mcg (women)

Vegetarians and vegans may get less selenium in their diets because plant foods may contain lower levels of selenium. Likewise, individuals who consistently eat organically grown food risk having a lower selenium intake. There may be a lower selenium content in meat and milk from animals fed organically grown feedstuffs than there is in the meat and milk from animals fed conventional feedstuffs [Alexander & Olsen 2023].

Selenium Supplementation and Selenium Status

In a study of 119 healthy men and women aged 50–64 years and living in the United Kingdom, Hurst et al found a mean baseline plasma selenium concentration of 95.7 mcg/L ± 11.5 mcg/L for all study participants. The researchers estimated the study participants’ daily intake from food to be 55 mcg of selenium. After they had administered 50 mcg of selenium from a selenium-enriched yeast preparation to one group of study participants for ten weeks, they measured a mean plasma selenium concentration of 118.3 ± 13.1 mcg/L [Hurst 2010].

In the UK study, the participants had baseline plasma levels somewhat higher than are typical in Nordic and Baltic countries. For the UK study participants, an intake of 55 mcg/day of selenium from food plus 50 mcg/day of selenium from supplementation resulted in the plasma SELENOP concentration’s reaching a plateau [Hurst 2010].

Tolerable Upper Intake Level for Selenium

At higher intakes selenium may cause adverse effects. Therefore, in order to protect the population the European Food Safety Authority [EFSA 2023] and the Nordic Nutrition Recommendations [Blomhoff 2023] have established 255 mcg/day in adults as the tolerable upper intake level.

Selenium Intakes and Disease Prevention

There is some clinical evidence that increased selenium intakes may reduce risk of cardiovascular disease and the risk of some cancers in individuals with low selenium intakes and status [Kuria 2021; Kuria 2020]. Increased selenium intakes by individuals with replete selenium status do not seem to benefit from increased selenium intakes [Alexander & Olsen 2023].

Conclusion: selenium is essential to good health

Adequate intake of selenium is needed for the synthesis of 25 known selenoproteins with a variety of biological functions.

Plasma selenoprotein P concentrations are a useful biomarker of selenium status in populations with relatively low selenium status.

Plasma selenium status of about 110 mcg/L seems to be needed for the achievement of optimal plasma selenoprotein P status.

A daily intake of about 80 to 90 mcg selenium in women and men from food and selenium-enriched supplements optimizes the plasma selenoprotein P concentration.

Individuals with lower or higher initial plasma selenium levels may need somewhat more or less selenium supplementation.

Selenium supplementation is not indicated for individuals with plasma selenium concentrations above 125 mcg/L [Winther 2020].


Alehagen U, Aaseth J, Alexander J, Johansson P, Larsson A. Supplemental selenium and coenzyme Q10 reduce glycation along with cardiovascular mortality in an elderly population with low selenium status – A four-year, prospective, randomised, double-blind placebo-controlled trial. J Trace Elem Med Biol. 2020 May 4;61:126541.

Alexander J, Olsen AK. Selenium – a scoping review for Nordic Nutrition Recommendations 2023. Food Nutr Res. 2023 Dec 28;67.

Blomhoff R et al. Nordic Nutrition Recommendations 2023. Copenhagen: Nordic Council of Ministers, 2023.

EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA). Scientific opinion on the tolerable upper intake level for selenium. EFSA J. 2023 Jan 20;21(1):e07704.

Haug A, Graham RD, Christophersen OA, Lyons GH. How to use the world’s scarce selenium resources efficiently to increase the selenium concentration in food. Microb Ecol Health Dis. 2007 Dec;19(4):209-228.

Hurst R, Armah CN, Dainty JR, Hart DJ, Teucher B, Goldson AJ, et al.. Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial. Am J Clin Nutr 2010; 91(4): 923–31.

Kuria A, Tian H, Li M, Wang Y, Aaseth JO, Zang J, Cao Y. Selenium status in the body and cardiovascular disease: a systematic review and meta-analysis. Crit Rev Food Sci Nutr. 2021;61(21):3616-3625.

Kuria A, Fang X, Li M, Han H, He J, Aaseth JO, Cao Y. Does dietary intake of selenium protect against cancer? A systematic review and meta-analysis of population-based prospective studies. Crit Rev Food Sci Nutr. 2020;60(4):684-694.

Lemming EW & Pitsi T. The Nordic Nutrition Recommendations
2022 – food consumption and nutrient intake in the adult population
of the Nordic and Baltic countries. Food Nutr Res 2022; 66: 1–10.

Stoffaneller R, Morse NL. A review of dietary selenium intake and selenium status in Europe and the Middle East. Nutrients. 2015 Feb 27;7(3):1494-537.

Winther KH, Rayman MP, Bonnema SJ, Hegedüs L. Selenium in thyroid disorders – essential knowledge for clinicians. Nat Rev Endocrinol. 2020 Mar;16(3):165-176.

The information presented in this review article is not intended as medical advice. It should not be used as such.


Leave a Reply

Your email address will not be published. Required fields are marked *