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Selenium and Cancer Prevention – the Evidence

The evidence for the use of selenium supplementation in cancer prevention is still inconclusive. Rataan et al suggest that the fault may lie in the design of the existing studies. At least two factors have contributed to this lack of conclusive evidence:

  • the use of different compounds in the tests of selenium and cancer
  • the different blood selenium levels of the study participants at baseline
Cancer patients
Selenium supplementation of individuals with low dietary intakes of selenium may help prevent the development of certain types of cancer.

As an example, Rataan et al cite the differences between the Nutritional Prevention of Cancer (NPC) trial and the Selenium and Vitamin E Cancer Prevention Trial (SELECT). In the NPC study, the researchers used a selenium-enriched yeast supplement. This yeast formulation contained mostly selenomethionine but also contained several other selenium species including Se-methylselenocysteine. In the SELECT study, the researchers used a 100% selenomethionine supplement. It now seems clear that the chemopreventive effect of selenium that was seen in the NPC study but not seen in the SELECT study must have come from some selenium species other than selenomethionine. The most likely chemopreventive selenium species is the Se-methylselenocysteine [Rataan 2022; Marshall 2017]. read more

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Selenium Protects Against Methylmercury in Fish

The health benefits of eating fish outweigh the health risks. This is especially true when we have sufficient dietary selenium intake and sufficient selenium status to 1) give a protective effect against methylmercury and 2) serve other biological purposes [Jorge 2024].

Salmon dinner contains selenium
Fatty fish such as herring, mackerel, and salmon are especially good sources of omega-3 fatty acids, protein, selenium, and vitamin D. Eating fatty fish regularly may reduce the risk of heart disease and stroke and enhance brain health.

To varying degrees, all fish contain some mercury. The mercury in fish and seafood is primarily in the form of methylmercury. Unchecked, the methylmercury targets the nervous system. It disrupts cellular processes. Too much exposure can lead to a loss of muscular coordination and to a loss in cognitive function. Accordingly, the presence of mercury could be a health risk for people who eat fish regularly [Jorge 2024].

Fortunately, many edible fish contain selenium in molar concentrations adequate to sequester the methylmercury in the fish and to render it less harmful. Ralston & Raymond have developed criteria for the calculation of selenium health based values. The calculations are based on the relative molar concentrations of mercury and selenium in various types of fish [Ralston 2016]. read more

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Selenium and Type 2 Diabetes

Selenium supplementation and the possible risk of developing type 2 diabetes, what do we know? This is a complex issue. Many different biological, hormonal, and environmental factors have an effect on the relationship.

Selenium and diabetes interrelationship
Observational evidence points to relevant sex differences in the selenium-diabetes interrelationship. There may be potential harmful effects in men living in selenium-rich areas and in men with high habitual selenium intake. Research shows potential benefits of selenium on diabetes risk in women selenium-deficient areas or in women with low selenium intake.

In a 2024 review, Demircan and a selenium research team headed by Prof Lutz Schomburg, Charité Berlin, investigated the current evidence for a relationship between selenium and type 2 diabetes. Recent evidence points to selenium intake and serum selenium status as relevant factors in the study of type 2 diabetes complications and prognosis.

Two studies based on data from the National Health and Nutrition Examination Survey (NHANES) in the United States have identified selenium intake and serum selenium status, respectively, as associated with the improved survival of type 2 diabetes patients [Demircan 2024]. read more

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Selenium and Graves’ Disease

Graves’ disease is an autoimmune disease. It is the most common cause of hyperthyroidism, i.e., overactive thyroid disorder. Ultimately, it is the overproduction of thyrotropin receptor (TRAb) antibodies that results in hyperthyroidism. Over time, Graves’ disease causes extensive damage to thyroid gland cells and tissues [Song 2023].

Thyroid system
In Graves’ disease, the thyroid gland produces too much thyroid hormone, a condition called hyperthyroidism. Attribution: Wikimedia Commons.

Oxidative stress appears to play an important role in Graves’ hyperthyroidism. Oxidative stress is the medical term for a disruption of the balance between harmful free radical oxidants and protective antioxidants. The increased production of reactive oxygen
radicals and inflammatory cytokines drives the development and progression of Graves’ disease [Song 2023]. read more

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Selenium and Vitamin D for Thyroid Health

Supplementation with selenium and vitamin D can improve the prognosis of type 2 diabetes mellitus and Hashimoto’s thyroiditis. Adding a daily dose of selenium and vitamin D to conventional diabetes medication can give significant health benefits [Yu 2024].

Selenium and Vitamin D for Type 2 Diabetes and Thyroid Disorder
A Chinese study suggests that combining conventional diabetes medicine with selenium and vitamin D supplements  reduces the levels of TSH and TPOAb and blood glucose and blood lipids in patients with concomitant type 2 diabetes and Hashimoto’s thyroiditis.

Researchers at Hunan University of Chinese Medicine, Hunan Province, China, recommend 100-200 mcg/day of selenium and 100 mcg/day of vitamin D for three to six months for patients with Hashimoto’s thyroiditis and especially for Hashimoto’s thyroiditis patients with concomitant type 2 diabetes [Yu 2024].

A 2024 study by Feng et al has shown that adding 200 mcg of selenium daily and 100 mcg of vitamin D to standard anti-diabetic drugs significantly improved thyroid function, thyroid antibodies, blood glucose, and blood lipids in type 2 diabetes patients who were also diagnosed with Hashimoto’s thyroiditis. read more

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Selenium Supplementation and COVID-19

There is, at present, an ongoing scientific debate about selenium supplementation and the possible prevention of COVID-19 disease. What is the evidence that selenium supplementation of individuals with sub-optimal selenium status might help to prevent the infection?

Margaret P. Rayman, selenium researcher
Margaret P. Rayman, Professor of Nutritional Medicine at the University of Surrey in the United Kingdom, is a long-time researcher into the effects of selenium and iodine on human health.

The answer from a group of longstanding selenium researchers is that selenium supplementation does not have “a sufficient direct antiviral effect to prevent infection.” Instead, selenium supplementation acts “by decreasing the harmful effects of the virus on the host” [Rayman 2024].

Selenium supplementation “does not necessarily prevent infection but rather decreases the severity and mortality resulting from the infection” [Rayman 2024]. The important thing to focus on is the interaction between the human host selenium status and infectious virus strain and virulence [Beck 2003]. read more

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Selenium: Why We Need It

In an online article in the Cleveland Clinic’s Health Essentials series, the registered dietician Kayla Kopp explains that selenium is an essential trace element that helps thyroid gland function and reproductive function, among other health benefits [Cleveland Clinic 2023].

Hospital care
The Cleveland Clinic article about the essential trace element selenium highlights the effect of selenium on thyroid health, reproductive health, asthma management, and cancer.

What does it mean that selenium is an essential trace element? Answer: our bodies need adequate selenium to function well. However, our bodies cannot synthesize selenium. We have to get our selenium from our food.

What are the health benefits of adequate selenium intake and adequate selenium status? Answer: Kopp says that selenium is important for the following reasons [Cleveland Clinic 2023]:

  • helps to protect our cells from damage
  • promotes good thyroid function
  • promotes good reproductive function
  • plays a role in DNA synthesis

Selenium Supports Thyroid Health

The thyroid gland is responsible for producing and releasing the hormones that control our metabolism. The metabolism rate is what determines how rapidly or slowly our bodies convert food into energy. The selenium we absorb from our food or from supplements gets converted into selenoproteins. These selenoproteins then help to regulate our thyroid hormones [Cleveland Clinic 2023]. read more

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Correcting Selenium Deficiency in Thyroid Disorders

Selenium supplementation. There seem to be two different approaches. One approach regards selenium supplementation as a direct pharmaceutical treatment. For example, it is considered a form of medication administered to thyroid disorder patients. Alone or together with thyroid disorder medication, the selenium supplementation is intended to 1) alleviate symptoms, 2) slow the progression of the disorder, and 3) perhaps provide a cure [Schomburg 2019].

Selenium researcher Urban Alehagen
Data from the Swedish KiSel-10 study show that combined daily selenium and Coenzyme Q10 supplementation has a beneficial effect on thyroid hormones and quality of life. outcomes.

A second approach to selenium supplementation does not regard the administration of selenium as a pharmaceutical intervention. Rather, the second approach considers selenium supplementation to be a nutritional intervention designed to address and correct a deficiency condition. This approach recognizes that both sub-optimal selenium status and selenium deficiency limit the body’s expression of vital selenoproteins. These selenoproteins are needed to minimize health risks and to alleviate disease symptoms. Supplemental selenium can be necessary to enable the full endogenous expression of selenoproteins [Schomburg 2019]. read more

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Selenoprotein P for Better Quality of Life and Longevity

In a KiSel-10 trial sub-study, Prof. Urban Alehagen and a team of researchers have observed a positive association between the levels of serum selenoprotein P (SELENOP) and the serum levels of both total selenium and the seleno-enzyme glutathione peroxidase GPx3. Accordingly, the researchers noted that the serum SELENOP concentration level can serve as a useful biomarker for the selenium status of individual study participants and of individual patients [Alehagen 2024].

Prof Urban Alehagen - selenium researcher
Prof Urban Alehagen is the lead researcher on the KiSel-10 trial of the effect of combined selenium and Coenzyme Q10 supplementation on the quality of life and longevity of elderly Swedish citizens with low dietary selenium intakes.

Important to note here is that daily supplementation with 200 mcg of selenium from a selenium-enriched yeast preparation induced significantly higher serum concentrations of SELENOP in elderly community dwelling Swedish citizens, average age: 77 years. In the active treatment group, the selenium supplementation resulted in the saturation of SELENOP in the blood at a serum selenium level of 146 mcg/L. The selenium supplementation also resulted in a saturation of GPx3 at a serum selenium level of 99 mcg/L. This positive association between the level of SELENOP, on the one hand, and serum selenium and GPx3, on the other hand, is in agreement with the existing research literature [Alehagen 2024]. read more

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Selenium and Hashimoto’s Thyroiditis

Hashimoto’s disease is an autoimmune disease. It is a disease that causes underactive thyroid (hypothyroidism). The body’s own immune-system cells attack the cells of the thyroid gland and gradually break them down and destroy them. This, of course, has a detrimental effect on thyroid gland function and on important metabolic processes in the body.

Selenium and thyroid gland function
The thyroid gland regulates energy metabolism, heart rate, breathing, digestion, body temperature, mental activity, and other body processes. Adequate selenium intake is necessary for thyroid hormone production.

Hashimoto’s is a bit tricky. In its early development and progression, there may not be any obvious symptoms. Eventually, such symptoms as fatigue and lethargy and weight gain will make themselves manifest. Hashimoto’s thyroiditis is a debilitating disease. It lessens a person’s quality of life. It tends to affect women more than men.

Of all the organs in the body, the thyroid gland has the highest concentration of selenium. It is a greedy organ with respect to selenium. An adequate intake of selenium can lessen the severity of hypothyroidism symptoms and is associated with lowered levels of autoimmune thyroid peroxidase antibodies. read more