What Is Selenium Deficiency?

Have you ever wondered how important is selenium in maintaining good health?

Selenium is an indispensable nutrient for sustaining overall health.  Naturally obtained through our diet, it has both positive and negative effects on our well-being. It can be found in a variety of foods, occasionally introduced for fortification or can be taken as a supplement.

Specific proteins, known as selenoproteins, have selenium as a critical component in their structure. Many experts think that selenium acts in the body through these proteins. So far, about 25 different selenoproteins have been identified in our cells and tissues.¹

In our body, selenium is stored in muscles, however, the thyroid holds a larger supply of selenium. This selenium when integrated into selenoproteins helps the thyroid work properly.

Apart from supporting the thyroid, selenium also serves other functions such as:

• Acting as an antioxidant to protect against free radicals
• Promoting reproduction
• Assisting the immune system in fighting off infection
• Facilitating DNA production and synthesis 

Over the last few decades, scientists have focused on understanding the importance of selenium for our health.¹

In this article, we delve into the importance of selenium for our well-being. We cover its functions, role within selenoproteins, dietary sources, and potential risks exploring how it contributes to our overall health.

What is selenium deficiency?

Selenium is a trace mineral, meaning that our body only requires a small amount of it.

When selenium intake is inadequate, it can lead to a condition known as selenium deficiency, usually due to foods with a lower amount of selenium in a particular region.

It is estimated that selenium deficiency impacts a range of 500 million to 1 billion people worldwide. In the US selenium deficiency is uncommon due to the abundance of this mineral in soil in North America. However, in most parts of Europe, soil selenium content is lower than that in the US, though still generally sufficient.² 

Selenium deficiency has been linked with

• Infertility
• Cardiovascular disease
• Cognitive decline (changes in mental abilities)
• Myodegenerative diseases (conditions where muscle health declines)
• Possibly cancer

Two specific diseases have been associated with selenium deficiency:

1. Keshan Disease, a form of cardiomyopathy (disease of heart muscles).³
2. Kashin-Beck Disease, which can lead to osteoarthropathy (involving bones and joints).⁴

What are the dietary sources of selenium?

Selenium in the diet can be obtained from both plant and animal sources.

The selenium levels in plants are closely linked to the selenium present in the soil. The way selenium is distributed within the soil is influenced by many different factors. The type of rocks and minerals present in that soil, the plants that grow there, human activities, the pH and the local climate are some of these. All these factors together determine how much selenium plants can take up from the soil and how it affects our health.

Animals that consume plants containing selenium are generally good sources of selenium, especially fish, seafood, poultry and beef. 

Brazilian nuts, shiitake mushrooms seafood, and organ meats are very good sources of selenium. However, most selenium is taken from bread, cereals, eggs, poultry and red meat. Other foods containing selenium are beans, lentils, brown rice, fortified cereals, button mushrooms green vegetables, and cottage cheese.

What are the recommended amounts of selenium?

Recommended Dietary Allowance (RDA)–For adults aged 19 and above, the daily recommended intake of selenium is 55 micrograms. However, pregnant women need around 60 micrograms, while breastfeeding women need about 70 micrograms per day

Tolerable Upper Intake Level (UL)–The maximum daily recommended amount of selenium that is unlikely to cause any harmful effects on health is 400 micrograms for adults aged 19 and above, including pregnant and breastfeeding women.

Who might be at risk of not getting enough selenium?

 The following groups are at an increased risk of having insufficient intakes of selenium.

• People living in regions with insufficient selenium levels
• People undergoing kidney dialysis treatment
• People who have HIV

What impact does selenium have on health?

Selenium is an essential part of our defence mechanism against oxidation, which safeguards our cells from DNA damage. Because of this, researchers have studied if selenium can be used as a way to prevent diseases such as cancer, heart disease or diabetes.  Selenium is also necessary for reproduction brain health and strong immune function.

Reproduction

Selenium is essential for testosterone synthesis and the formation and development of normal sperm cells. Large concentrations of selenium are found in testis influencing sperm quality and overall male fertility. However, data regarding female fertility and selenium are limited.²

Cardiovascular health

Selenoproteins have antioxidant and anti-inflammatory properties that may offer protection against cardiovascular disease. While some studies have shown that low selenium in the blood is associated with an increased risk of developing heart diseases, others do not support this.

The current knowledge isn't strong enough to suggest that taking selenium supplements could protect against cardiovascular disease.

Thyroid disease

In our body, the thyroid contains the highest amount of selenium, which is vital for regulating its function.

Some women during pregnancy have specific thyroid-related antibodies which can cause their thyroid hormone levels to drop and to have a less active thyroid after giving birth.  

A study suggested that pregnant women, with these thyroid antibodies could reduce the risk of developing thyroid problems after childbirth by taking selenium supplements during pregnancy.⁶ However, additional research is needed to understand the role of selenium in thyroid disease.

Brain and mental health

Research has indicated that selenium might have a protective role against postnatal depression and may be viewed as a helpful supplementary treatment for those dealing with depression.⁵

Cancer

Selenium might help prevent cancer due to its DNA repair, antioxidants or immune system properties. Several studies have suggested a link between higher selenium levels and a lower risk of certain types of cancer such as prostate, lung, colorectal, bladder, gastric, skin and oesophagal. However, the results between studies are not consistent. The FDA emphasized the need for further research to confirm the protective role of selenium against cancer.

Can selenium be toxic?

Selenium is harmful when taken in excess. High consumption for prolonged periods can cause different health problems such as stomach upset, hair loss and muscle tremors but also more serious conditions such as heart attack, kidney failure or respiratory difficulties. 

Brazilian nuts contain exceedingly high amounts of selenium (68–91 mcg per nut) even if grown in selenium-poor soil. If you consume too many or if you taking supplements that contain selenium above the RDA you can exceed the upper limit.  

Consuming too much selenium for an extended period can result in the following:

• Bad breath or metallic taste
• Diarrhoea
• Hair or nail loss
• Nail brittleness or discolouration
• Skin rash or lesions
• Irritability
• Tooth discolouration
• Muscle tenderness 
• Nervous system problems 

Summary

Selenium is a vital component of human health. It is naturally present in many foods, added for fortification processes or can be taken as a supplement. It is incorporated into certain proteins called selenoproteins that exert essential functions, such as supporting the thyroid,  serving as an antioxidant, promoting reproduction, boosting immunity, and helping with DNA synthesis.

Scientists have extensively studied selenium's health importance. This is particularly crucial for vulnerable groups like those in low-selenium areas, on dialysis, or with HIV. It has been suggested that also plays a role in cancer, heart disease, and diabetes.

However, excessive selenium intake can be harmful, causing discomfort or severe problems. Maintaining the right balance is essential. Always consult with your doctor before taking selenium supplements.