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Selenium and Mercury Toxicity

Nick Ralston has spent many years doing research into the interaction between selenium and mercury in the human body. He is a research scientist and adjunct professor in the Department of Earth System Sciences and Policy at the University of North Dakota. His research has changed how scientists and regulators think about mercury’s impact on human health. Now, scientists regard selenium status as a central factor in determining the risk of mercury toxicity [Ralston 2018; Ralston 2010].

Selenium basic facts
Selenium and mercury interact strongly with one another. Selenium can bind to mercury and protect brain from damage. However, mercury’s binding to selenium reduces the amount of selenium available for antioxidant defense and thyroid function.

Previously, the most common explanation of mercury toxicity was that mercury exposure directly caused oxidative stress. Selenium’s binding with mercury, it was thought, reduced the risk of oxidative stress and reduced the risk of mercury toxicity. read more

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Selenium and Diabetes and Insulin Resistance

What do intervention studies show about selenium supplementation and diabetes risk?

Diabetes finger prick
Selenium supplementation studies show improved insulin sensitivity in adults with diabetes and insulin resistance who have low selenium status.

A 2026 review has found that selenium supplementation improves insulin sensitivity in individuals who are low in selenium. The effect is especially evident in adults with diabetes or insulin resistance. The effect of selenium supplementation in women with polycystic ovary syndrome and in postmenopausal women is less unequivocal. Moreover, studies show that selenium supplementation of individuals with replete selenium status does not make sense [Morales-Juárez 2026].

What other effects, in addition to improving insulin sensitivity, does selenium supplementation have in individuals with diabetes or insulin resistance? read more

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Selenium and Human Health

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.
Younger woman with elderly woman
Good health in our senior years depends in part on sufficient selenium intake and status. Selenium is an essential trace element.

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]. read more

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Selenium for Inflammatory Bowel Disease

What is Inflammatory Bowel Disease (abbreviated as IBD)? IBD is a complex disorder in the gastrointestinal tract. Many factors influence the development of IBD: genetics, immune system dysfunction, gut microbiota disturbances, and environmental influences. The prevalence of IBD worldwide is steadily rising [Gorini & Tonacci 2025].

Pain au chocolat
Individuals with Inflammatory Bowel Disease can eat carbohydrates and chocolate in moderation. Tolerance may  depend upon whether the individual is in a flare or in remission. Selenium status is often low in individuals diagnosed with IBD.

What is typical of IBD? Primarily, IBD includes Crohn’s disease and ulcerative colitis. IBD involves a chronic inflammatory condition in the gastrointestinal tract. The symptoms of IBD vary. They include abdominal pain, diarrhea, nausea, vomiting, and weight loss [Gorini & Tonacci 2025].

Typically, Crohn’s disease is more prevalent in women. Ulcerative colitis is more common in men. Gorini & Tonacci [2025] report that women diagnosed with IBD tend to have a worse quality of life characterized by more anxiety and depression than is the case for men. Men, on the other hand, are more likely to have surgery and generally have a higher risk of mortality. read more

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Selenium and Coenzyme Q10 – A Good Heart Health Combination?

What makes selenium and Coenzyme Q10 a good heart health combination supplement? Here, of course, we are talking about supplementation of individuals who have low selenium and CoQ10 blood levels.

Dr. Jan Alexander, Norwegian selenium researcher
Guest author Dr. Jan Alexander, MD, Ph.D., has been the co-author of the selenium scoping article [Alexander and Olsen 2023] for the 2023 Nordic Nutrition Recommendations and several KiSel-10 sub-studies.
How much selenium is enough? How much Coenzyme Q10 is enough? Roughly estimated, individuals with serum selenium levels below 80 mcg/L may need more selenium than they are getting in their diets. The same estimate applies to individuals with plasma CoQ10 levels below 0.8 mg/L. The goal of the selenium supplementation is to raise the circulating selenium levels to approximately 110-125 mcg/L [Alexander and Olsen 2023, Larsen 2024]. The purpose of the CoQ10 supplementation is to raise the circulating CoQ10 levels to about 2.5 mg/L [Langsjoen 2014]. read more

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Selenium and Selenoproteins and Health

A 2025 review summarizes the biological activities and health functions of important selenoproteins. The selenoproteins play a role in antioxidant and anti-inflammation defense, cancer prevention, cardiovascular health, fertility, immune system regulation, and defense against viral infections including COVID-19 [Shahidin 2025].

Greenland
Traditional food on Grønland was rich in selenium. Historically, the Inuit people had high selenium intake and high serum selenium levels. Selenium is an essential micronutrient that contributes to good health and longevity.

Selenium deficiency leads to insufficient synthesis of the selenoproteins. Generally, selenium researchers regard serum selenium concentrations under 70 mcg/L as deficiency levels. Serum selenium concentrations below 45 mcg/L indicate severe selenium deficiency [Winther 2020; Schomburg 2021].

The point is that selenium deficiency and insufficient selenoprotein synthesis can impair antioxidant and anti-inflammation defense, weaken immune function, and disturb thyroid hormone metabolism. Likewise, selenium deficiency can contribute to neurological and endocrine disorders. Selenium deficiency can have a detrimental effect on cardiovascular health. Selenium deficiency is associated with increased incidence of Keshan disease and Kashin–Beck disease [Shahidin 2025]. read more

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Selenoprotein P and Heart Health

Low serum concentrations of selenoprotein P (SELENOP) are an indication of increased heart health risks. Low serum SELENOP is strongly associated with the following risks:

  • increased risk of a first cardiovascular event
  • increased risk of cardiovascular mortality
  • increased risk of all-cause mortality 
Scene from Scandinavia - a selenium-poor region.
Selenium is a scarce resource. It is a non-renewable resource. Selenium deficiency is a health problem for one half to one billion people in the world. The UK, the Nordic countries, and the Baltic countries are among the selenium-poor regions in the world.

This is the conclusion from a relatively large study of adults in Sweden. The study participants had no history of cardiovascular disease at the beginning of the study [Schomburg 2019].

There were 3,531 non-smokers and 835 smokers enrolled in the study in Sweden. At the end of the study, the study participants at increased risk of cardiovascular disease had a mean serum SELENOP level below 4.3 mg/L SELENOP. This serum concentration of SELENOP corresponds to serum selenium concentrations of less than 70 mcg/L [Schomburg 2019]. read more

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Selenium and Sports Nutrition

In sports, in exercise, and in training, selenium is a frequently overlooked micronutrient. Selenium’s fundamental importance to human health is not well known. Researchers are beginning to conduct studies of selenium in sports nutrition and skeletal muscle health. Their studies show that selenium and selenoproteins play an important role in maintaining skeletal muscle function. Studies show that selenoproteins delay exercise fatigue and muscle aging [Wang 2025].

Football player
In selenium-poor regions of the world, athletes and individuals who exercise strenuously may need a daily selenium supplement.

Optimal selenium intake from food and from supplements (when necessary) can mitigate aging-related muscle decline. Selenium can help to prevent exercise-associated musculoskeletal injuries. There is a need for more clinical studies of the effect of selenium supplementation on skeletal muscle health in selenium-poor regions [Wang 2025]. read more

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Selenium Essential for Human Health

Selenium is a trace element that is essential for good human health. Essential means that selenium is a micronutrient that the body must have but cannot synthesize for itself. Its supply must come from food and, if necessary, from supplements. What the body does synthesize when it has an adequate supply of the element selenium is first the amino acid selenocysteine and then selenoproteins into which the selenocysteine molecules are incorporated [Bai 2024].

Nurse portrays good health
Good health depends upon adequate selenium intake. In selenium-poor regions, selenium supplementation may be necessary.

Accordingly, selenium is an indispensable component of selenoprotein P and numerous other selenoproteins. Among these selenoproteins are several vital selenoenzymes, e.g., the glutathione peroxidases (GPxs), the thioredoxin reductases (TrxRs), and the iodothyronine deiodinases (DIOs). Through the activity of the selenoproteins, selenium has many biological functions, i.e., antioxidant activity, anti-inflammatory effects, enhanced immune system function, enhanced reproductive capacity, protection of the cardiovascular system, and regulation of thyroid function. In figure 6 of their paper, Bai et al list the best documented selenoproteins and their known functions [Bai 2024]. read more

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Selenium for Adjuvant Cancer Treatment

Cancer treatment. What do we know at the present time about the effectiveness of selenium as an adjuvant treatment in cancer patients?
In a 2024 systematic review, researchers have evaluated the existing evidence from data from 12 studies with 2,483 adult patients undergoing cancer treatment. The types of cancer included non-Hodgkin lymphoma, head and neck cancer, thyroid cancer, acute myeloid or acute lymphocytic leukemia, stage I non-small lung cancer, breast cancer, cervical and endometrial cancer, prostate cancer, and non-invasive urothelial carcinoma [Krannich 2024].

Cancer patient
More information is needed about the effects of adjuvant treatment of cancer patients with selenium supplements. Similarly, more information is needed about the concurrent use of selenium supplements in patients receiving chemotherapy and radiation therapy.

The researchers’ analysis of the available data does not give a clear picture of the efficacy of selenium administration to adult cancer patients. One reason is that several of the evaluated studies did not report measurements of the patients’ serum selenium levels at the beginning or the end of the study. The studies that did report serum selenium levels used different ways to measure selenium levels. Moreover, the duration of the selenium administration and the type of selenium preparation and the dosage varied from study to study [Krannich 2024]. read more