What is the importance of selenium to human health? Selenium is an essential trace element. That selenium is essential to our health means two things:
- Our bodies cannot synthesize selenium for us. We must get it from our diets.
- Our bodies need selenium for physiological functions such as growth, metabolism, and reproduction.
How does selenium work in the body? Primarily, elemental selenium works as a component of selenoproteins – proteins that contain selenium. These selenoproteins have important biological functions in the human body, e.g., antioxidant defense, immune function, thyroid hormone metabolism, etc [Alexander & Olsen 2023].
What are the Recommended Daily Intake Levels for Adults?
The 2023 Nordic Nutrition Recommendations established Adequate Intake levels as follows [Blomhoff et al 2023]:
- Women: 75 mcg/day
- Men: 90 mcg/day
Who is Likely to Have Low Selenium Intakes?
The human intake of selenium varies considerably from region to region in the world. The selenium intake depends upon the selenium content of the soil and the crops in the region. For example, soil selenium is low in most area in the Nordic and the Baltic countries. The average intake of selenium in these countries, except Finland, is likely to be below recommended intake levels [Blomhoff et al 2023].
Note: Finland is an exception because Finland fertilizes its soil with selenium. There is not enough available selenium to make selenium fertilization feasible for the many selenium-poor countries and regions in the world.
Vegetarians and vegans are especially at risk of low selenium intakes if they rely on plant-based foods with low selenium content [Alexander & Olsen 2023]. They may need selenium supplements.
What are Blood Biomarkers for Selenium Status?
It is possible to measure the level of selenium in serum, typically in mcg/L or ng/mL.
However, measuring the concentration Selenoprotein P in plasma is thought to be the most appropriate biomarker of selenium status. Selenoprotein P is the primary circulating form of selenium. It is responsible for transporting selenium to the cells and tissues. Selenoprotein P makes up roughly 50 to 60% of plasma selenium in selenium-replete individuals [Alexander & Olsen 2023].
What are Optimal Serum or Plasma Levels of Selenium?
In a UK supplementation study that lasted 12 weeks and used doses of selenized yeast of 50, 100, and 200 mcg selenium/day in addition to a food intake of 55 mcg/day, researchers found that maximal expression of selenoprotein P correlated to a plasma selenium concentration of 125 mcg/L [Hurst et al 2010].
What are the Tolerable Upper Intake Levels for Selenium?
For adults including pregnant and lactating women, the 2023 Nordic Nutrition Recommendations set the tolerable upper intake levels at 255 mcg/day, food intake and supplements combined. The NNR2023 has adopted this safety level from the European Food Safety Authority [Blomhoff et al 2023].
Chronic high intakes of selenium – 330-450 mcg/day – can cause selenium poisoning (called selenosis). Selenosis can result in brittle nails, hair loss, and gastrointestinal disturbances [Blomhoff et al 2023].
How does Selenium Status Affect the Risk of Cardiovascular Disease?
In individuals with low selenium status but not in selenium replete individuals, increased selenium intake may reduce the risk of cardiovascular disease [Alexander & Olsen 2023].
In the KiSel-10 study in Sweden, Prof. Urban Alehagen et al enrolled elderly individuals low in selenium (mean selenium level> 67.1 mcg/L) in a randomized controlled clinical trial to test the efficacy of combined selenium and coenzyme Q10 supplementation daily for four years. The combined supplementation with 200 mcg/day of selenium and two times 100 mg/day of coenzyme Q10 significantly reduced cardiovascular mortality in elderly study participants who had low selenium status at the study start [Alehagen et al 2016].
What are Low and Sub-Optimal Selenium Levels?
It seems plausible that serum or plasma selenium concentrations below 70 mcg/L constitute low (deficient) selenium levels. Serum or plasma selenium concentrations between 70 and 100 mcg/L suggest sub-optimal selenium levels.
The reasoning behind the cut-off points of 70 and 100 mcg/L is based on our knowledge of the circulating selenium levels that result in the saturation of glutathione peroxidase (GPx) in plasma. Typically, there will not be saturation of GPx activity if plasma selenium levels fall below 70 mcg/L [Alexander & Olsen 2023].
Similarly, there will not be saturation of platelet GPx if the plasma concentration of selenium is below 100 mcg/L [Alexander & Olsen 2023]. As noted above, the target level for serum or plasma selenium concentration is thought to be approximately 125 mcg/L, the level at which selenoprotein P activity will be optimal.
Conclusions: Selenium and Human Health
Human health requires adequate supply of selenium.
The soils and the crops in many regions of the world have poor selenium content.
Typically, we need enough selenium in our food and supplements, if necessary, to maintain a serum selenium status of about 125 mcg/L.
Except in special circumstances, we should not exceed intakes of 255 mcg of selenium per day.
Sources
Alehagen U, Alexander J, Aaseth J. Supplementation with selenium and Coenzyme Q10 reduces cardiovascular mortality in elderly with low selenium status. A secondary analysis of a randomised clinical trial. PLoS One. 2016 Jul 1;11(7):e0157541.
Alexander J, Olsen AK. Selenium – a scoping review for Nordic Nutrition Recommendations 2023. Food Nutr Res. 2023 Dec 28;67.
Blomhoff R, Andersen R, Arnesen EK, Christensen JJ, Eneroth H, Erkkola M, et al. Nordic Nutrition Recommendations 2023. Copenhagen: Nordic Council of Ministers; 2023.
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.
The information presented in this review article is not intended as medical advice. It should not be used as such.