Selenium: An Essential Mineral

Takeaways

• Selenium is a trace mineral vital for human health
• It supports thyroid function and immune system strength
• Selenium acts as a powerful antioxidant in the body
• Both deficiency and excess can cause health problems
• Food sources vary based on soil content and geography
• Supplementation may benefit some individuals

What Is Selenium?

Selenium is a trace mineral present in soil, water, and various foods. It’s a necessary nutrient for human health, although the body requires it in only small amounts. Swedish chemist Jöns Jacob Berzelius discovered selenium in 1817¹.

Initially, scientists believed selenium was harmful to humans. Later studies demonstrated its significance for well-being. In 1957, selenium was recognized as an essential nutrient for animals². By the 1970s, its role in human health became clearer.

Selenium has multiple functions within the body. It aids in the creation of selenoproteins, which are special proteins. These proteins are involved in:

• Making DNA
• Reproducing cells
• Preventing cell damage
• Regulating thyroid hormones

The human body cannot produce selenium; it must be obtained through diet or supplements. The amount found in foods depends on the selenium levels present in the soil where plants are grown or animals graze.

Natural Sources of Selenium

Selenium occurs naturally in a variety of foods. The amount varies based on the geographic location where the food was produced. Selenium levels in soil differ globally, which influences how much is absorbed by plants and animals.

Several factors affect the amount of selenium in soil, such as:

• Rainfall
• Soil pH
• Organic matter content
• Use of selenium-containing fertilizers

Foods that are good sources of selenium include:

• Brazil nuts
• Seafood (tuna, halibut, sardines)
• Organ meats (kidney, liver)
• Poultry
• Eggs
• Mushrooms
• Whole grains

Brazil nuts are exceptionally high in selenium. Consuming just one nut can exceed the daily recommended intake. However, the selenium content within Brazil nuts can vary significantly³.

Selenium content in crops differs by region. For instance, wheat from North America typically contains more selenium than wheat from Europe. This is attributed to variations in soil composition.

Selenium levels in animal products also differ. This depends on the animal’s diet. Grass-fed beef frequently contains more selenium than grain-fed beef because the plants they eat reflect the soil’s selenium content.

Selenium in the Body

Absorption and Distribution

The small intestine absorbs selenium from ingested food. The form of selenium affects how well it’s absorbed; organic forms, such as selenomethionine, are absorbed more efficiently than inorganic forms⁴.

Once absorbed, selenium is transported through the blood to different tissues. It is concentrated in the:

• Liver
• Kidneys
• Spleen
• Pancreas
• Testes

Selenium is also present in smaller amounts in other parts of the body. Here’s a breakdown of selenium concentrations in various areas:

Metabolism

The body processes selenium through several steps. First, it’s converted into forms that cells can use. The primary usable form is selenocysteine, which is then utilized to create selenoproteins.

Selenoproteins perform many functions in the body. They:

• Act as antioxidants
• Help make thyroid hormones
• Support immune function
• Aid in reproduction

Glutathione peroxidase is an important selenoprotein. This enzyme protects cells from damage by neutralizing harmful molecules called free radicals.

Selenium’s role as an antioxidant is complex. It supports the formation and activation of antioxidant enzymes. These enzymes circulate throughout the body, protecting cells in different tissues from oxidative stress.

Health Benefits of Selenium

Thyroid Function

Selenium is critical for thyroid health. The thyroid gland contains more selenium per gram than any other organ. Selenium helps produce and regulate thyroid hormones⁵.

Thyroid hormones control many bodily functions including:

• Metabolism
• Growth
• Development
• Body temperature

Insufficient selenium can hinder thyroid function. This may result in conditions such as:

• Hypothyroidism
• Hashimoto’s disease
• Graves’ disease

Some studies suggest that selenium supplements may benefit individuals with thyroid problems. However, further research is needed to confirm these findings⁶.

Immune System Support

Selenium strengthens the immune system. It aids the body in producing and utilizing white blood cells, which defend against harmful bacteria and viruses.

Research indicates that selenium may lower the risk of certain infections. For example, individuals with higher selenium levels may be less likely to contract:

• Influenza
• HIV
• Hepatitis C

Selenium also contributes to the production of antibodies. These proteins assist in identifying and neutralizing threats to our health.

Antioxidant Properties

Selenium is a potent antioxidant. It protects cells from the damage caused by free radicals, which are unstable molecules that can harm DNA and cells.

Here’s how selenium functions as an antioxidant:

1. It becomes part of antioxidant enzymes
2. These enzymes spread throughout the body
3. The enzymes neutralize free radicals
4. This prevents damage to cells and DNA
5. Over time, this may reduce the risk of chronic diseases

By counteracting oxidative stress, selenium may help prevent:

• Heart disease
• Some types of cancer
• Cognitive decline

Cognitive Health

Selenium might have a positive impact on brain function. Some studies connect higher selenium levels with improved cognitive performance⁷.

As we age, our brains become more susceptible to oxidative stress. Selenium’s antioxidant properties may help protect brain cells, potentially slowing cognitive decline.

Research in this area is still underway. Initial studies show promise, but more evidence is required. Scientists are investigating selenium’s role in:

• Memory
• Mood
• Alzheimer’s disease prevention

Cardiovascular Health

Selenium may promote heart health. Its antioxidant effects could protect against heart disease. Some studies suggest selenium might:

• Reduce inflammation
• Lower bad cholesterol levels
• Prevent blood clots

However, the evidence is inconsistent. Some research finds no clear relationship between selenium and heart health⁸. More studies are needed to fully understand this connection.

Selenium Deficiency

Causes

Selenium deficiency is uncommon in most countries. However, it can occur in regions with soil that has low selenium content. Other factors that may lead to a deficiency include:

• Poor diet
• Digestive disorders that impair absorption
• Kidney dialysis
• HIV infection

Individuals at higher risk of selenium deficiency include:

• Those living in low-selenium regions
• People with severe digestive issues
• Individuals on long-term intravenous feeding

Symptoms

Selenium deficiency often does not cause obvious symptoms. However, when symptoms do appear, they can include:

• Weakness
• Fatigue
• Hair loss
• Weakened immune system
• Fertility problems
• Mood changes

In severe cases, selenium deficiency can lead to more serious health issues. These may impact the heart, bones, and the immune system.

Health Consequences

Long-term selenium deficiency can have significant consequences. It may increase the risk of:

• Keshan disease (a type of heart problem)
• Kashin-Beck disease (a bone disorder)
• Thyroid dysfunction
• Weakened immune system
• Cognitive decline
• Cardiovascular disease

In areas with very low selenium intake, programs that include supplementation have been beneficial. They have lowered the occurrence of Keshan disease and other health problems⁹.

Selenium Toxicity

Causes

While selenium deficiency is uncommon, toxicity can occur as well. This typically happens from consuming too many supplements. It’s very rare to get too much selenium from food alone.

Risk factors for selenium toxicity include:

• Over-supplementation
• Accidental ingestion of selenium-containing products
• Living in areas with very high soil selenium levels

Symptoms

Signs of selenium overload can include:

• Garlic breath odor
• Nausea
• Diarrhea
• Skin rashes
• Brittle nails
• Hair loss

Severe cases might result in more serious symptoms:

• Nerve damage
• Fatigue
• Irritability
• Tremors
• Kidney failure

Health Consequences

Long-term high selenium intake may result in extended health issues. These could include:

• Type 2 diabetes
• Skin lesions
• Nervous system problems
• Cardiovascular issues

Some studies have associated high selenium levels with a higher risk of prostate cancer. However, additional research is needed to confirm this association¹⁰.

Recommended Intake

The amount of selenium needed varies based on age and life stage. Here are the Recommended Dietary Allowances (RDAs) for selenium:

These amounts are the average daily intake needed to meet the needs of most healthy individuals. Certain factors that could affect selenium needs include:

• Overall health status
• Medications
• Digestive issues
• Alcohol consumption
• Smoking

It’s important to understand that more is not always better. The upper limit for adults is 400 mcg per day. Intakes above this level could cause harm.

Selenium Supplements

Types

Selenium supplements are available in different forms. Common types include:

• Selenomethionine
• Sodium selenite
• Selenium-enriched yeast

Each form has varying absorption rates and effects within the body. Selenomethionine is often considered the most easily absorbed form¹¹.

Usage

Guidelines for taking selenium supplements include:

• Follow the dosage instructions on the label
• Don’t exceed the recommended daily allowance
• Take with food to improve absorption
• Spread doses throughout the day if taking higher amounts

It’s essential to consult a healthcare provider prior to starting any supplement. They can help determine if you need supplemental selenium and what the appropriate dosage is for you.

Safety

While selenium supplements can be helpful, they also come with some risks. Precautions to consider include:

• Don’t exceed the upper limit of 400 mcg per day
• Be aware of selenium content in multivitamins
• Watch for signs of toxicity
• Inform your doctor of all supplements you’re taking

Selenium can interact with certain medications, including:

• Some chemotherapy drugs
• Statins (cholesterol-lowering medications)
• Niacin
• Antacids

Always consult with a healthcare provider before combining selenium with any medications.

Selenium in Special Populations

Pregnancy and Breastfeeding

Selenium requirements increase during pregnancy and breastfeeding to support fetal growth and development. The RDA for pregnant women is 60 mcg daily, while for breastfeeding women, it’s 70 mcg daily.

Adequate selenium during pregnancy may help:

• Reduce the risk of preeclampsia
• Support fetal brain development
• Strengthen the baby’s immune system

However, excessive selenium can be harmful. Pregnant women should avoid high-dose supplements unless prescribed by a doctor.

Elderly

As people age, their bodies may not absorb nutrients as efficiently. This includes selenium. Older adults might need to be particularly mindful of their selenium intake.

Some studies suggest that higher selenium levels in older adults are associated with:

• Better cognitive function
• Reduced risk of depression
• Improved immune response

However, additional research is needed to confirm these advantages. Older adults should target the RDA of 55 mcg per day, unless otherwise advised by a doctor.

Athletes

Athletes may have increased selenium requirements because intense exercise can increase oxidative stress in the body. Selenium’s antioxidant properties might help counteract this.

Potential advantages of sufficient selenium for athletes may include:

• Reduced muscle damage
• Improved recovery
• Enhanced immune function

However, there isn’t evidence that extra selenium boosts performance. Athletes should prioritize obtaining enough selenium through a balanced diet. Supplements are seldom necessary unless advised by a sports nutritionist.

Selenium and Disease Prevention

Cancer

The relationship between selenium and cancer is intricate. Some studies suggest selenium might help prevent certain cancers, while others show no benefit or possible harm at higher doses.

Possible anti-cancer effects of selenium include:

• Reducing DNA damage
• Slowing tumor growth
• Enhancing immune function

However, results vary depending on the cancer type and individual factors. A large study called SELECT found that selenium supplements did not reduce prostate cancer risk¹². In some situations, high selenium levels might even increase risk.

Further research is necessary to clarify selenium’s role in cancer prevention. Currently, it’s best to get selenium from food sources instead of supplements.

HIV/AIDS

Selenium may play a role in HIV/AIDS management. People with HIV often have low selenium levels. This could be due to poor nutrition or the impact of the virus itself.

Studies have determined that selenium status can influence:

• Disease progression
• Immune function
• Quality of life in HIV patients

Some research indicates that selenium supplements might slow down HIV progression¹³. However, more studies are needed to verify these effects.

Individuals with HIV should discuss selenium intake with their healthcare team. Proper nutrition, including sufficient selenium, can support overall health and immune function.

Diabetes

The connection between selenium and diabetes is not yet clear. Some studies indicate that high selenium levels might increase the risk of diabetes. Others show no link, or even suggest a protective effect.

Possible effects of selenium on diabetes may include:

• Influencing insulin sensitivity
• Affecting blood sugar regulation
• Impacting oxidative stress in diabetic patients

A review of studies discovered that both very low and very high selenium levels might raise the risk of diabetes¹⁴. The safest approach is to strive for the recommended daily intake through food sources.

People with diabetes should discuss selenium intake with their doctor. They can help determine if supplements are necessary or potentially harmful.

Testing for Selenium Status

Measuring selenium levels in the body can be beneficial in certain situations. Common tests include:

• Blood tests (serum or plasma selenium)
• Hair analysis
• Nail clippings analysis
• Urine tests

Each testing method has advantages and disadvantages. Blood tests are most common but may not reflect long-term status. Hair and nail tests can show selenium levels over time, but are less accurate.

Interpreting selenium test results requires expert knowledge. Factors to consider include:

• Age
• Sex
• Diet
• Health conditions
• Medications

Normal selenium ranges can vary based on these factors. A healthcare provider can assist in making sense of test results. They will take your overall health and any symptoms into account when interpreting the numbers.

Selenium in the Food Industry

The food industry uses selenium in different ways. One typical practice is food fortification, which involves adding selenium to foods to improve their nutritional content.

Some products that may be fortified with selenium include:

• Bread
• Cereals
• Pasta
• Dairy products

Another method involves producing selenium-enriched foods. Farmers can do this by adding selenium to the soil or animal feed, which results in higher selenium content in crops and animal products.

Here’s a comparison of selenium levels in regular versus enriched foods:

Enriched foods can help prevent deficiencies in areas with low selenium levels. However, it’s important to monitor intake to avoid overconsumption.

Environmental Impact of Selenium

Selenium is a component in ecosystems worldwide. It’s vital for many plants and animals. However, excessive selenium can harm the environment.

In nature, selenium cycles through:

• Soil
• Water
• Air
• Living organisms

Human actions can disrupt this cycle. Sources of selenium pollution include:

• Coal combustion
• Mining operations
• Agricultural runoff
• Industrial processes

High levels of selenium in water can harm aquatic life. It can build up in fish, leading to deformities or reproductive issues.

Efforts to manage selenium in the environment include:

• Monitoring water and soil levels
• Treating contaminated areas
• Regulating industrial emissions
• Developing selenium-tolerant crops

Balancing human needs with environmental protection is an ongoing challenge. Researchers are working to find sustainable ways to manage selenium resources.

Future Research and Developments

Scientists are continually studying selenium’s effects on health. Current research topics include:

• Selenium’s role in cancer prevention and treatment
• Its impact on cognitive function and brain health
• Potential benefits for heart disease and diabetes
• Optimal intake levels for different populations
• New ways to measure selenium status in the body

Challenges in selenium research include:

• Variability in soil selenium levels worldwide
• Differences in how individuals metabolize selenium
• Interactions with other nutrients and medications
• Long-termeffects of selenium supplementation

Potential new applications of selenium in medicine and nutrition are developing. These include:

• Targeted selenium therapies for specific health conditions
• Development of new selenium-enriched foods
• Use of selenium nanoparticles in medical treatments
• Personalized selenium recommendations based on genetic factors

As research advances, our understanding of selenium’s role in health will increase. This could result in more effective methods to utilize this mineral for disease prevention and treatment.

FAQ: People Also Ask

1. Berzelius, J. J. (1818). Lettre de M. Berzelius à M. Berthollet sur deux métaux nouveaux. Annales de Chimie et de Physique, 7, 199-206.

2. Schwarz, K., & Foltz, C. M. (1957). Selenium as an integral part of factor 3 against dietary necrotic liver degeneration. Journal of the American Chemical Society, 79(12), 3292-3293. https://doi.org/10.1021/ja01569a087

3. Thomson, C. D., Chisholm, A., McLachlan, S. K., & Campbell, J. M. (2008). Brazil nuts: an effective way to improve selenium status. The American Journal of Clinical Nutrition, 87(2), 379-384. https://doi.org/10.1093/ajcn/87.2.379

4. Rayman, M. P., Infante, H. G., & Sargent, M. (2008). Food-chain selenium and human health: spotlight on speciation. British Journal of Nutrition, 100(2), 238-253. https://doi.org/10.1017/S0007114508922522

5. Schomburg, L., & Köhrle, J. (2008). On the importance of selenium and iodine metabolism for thyroid hormone biosynthesis and human health. Molecular Nutrition & Food Research, 52(11), 1235-1246. https://doi.org/10.1002/mnfr.200700465

6. Duntas, L. H., & Benvenga, S. (2015). Selenium: an element for life. Endocrine, 48(3), 756-775. https://doi.org/10.1007/s12020-014-0477-6

7. Cardoso, B. R., Ong, T. P., Jacob-Filho, W., Jaluul, O., Freitas, M. I. D., & Cozzolino, S. M. (2010). Nutritional status of selenium in Alzheimer’s disease patients. British Journal of Nutrition, 103(6), 803-806. https://doi.org/10.1017/S0007114509992832

8. Bleys, J., Navas-Acien, A., & Guallar, E. (2008). Serum selenium and diabetes in U.S. adults. Diabetes Care, 31(4), 741-746. https://doi.org/10.2337/dc07-1936

9. Xia, Y., Hill, K. E., Byrne, D. W., Xu, J., & Burk, R. F. (2005). Effectiveness of selenium supplements in a low-selenium area of China. The American Journal of Clinical Nutrition, 81(4), 829-834. https://doi.org/10.1093/ajcn/81.4.829

10. Lippman, S. M., Klein, E. A., Goodman, P. J., Lucia, M. S., Thompson, I. M., Ford, L. G., … & Coltman, C. A. (2009). Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA, 301(1), 39-51. https://doi.org/10.1001/jama.2008.864

11. Schrauzer, G. N. (2000). Selenomethionine: a review of its nutritional significance, metabolism and toxicity. The Journal of Nutrition, 130(7), 1653-1656. https://doi.org/10.1093/jn/130.7.1653

12. Klein, E. A., Thompson, I. M., Tangen, C. M., Crowley, J. J., Lucia, M. S., Goodman, P. J., … & Baker, L. H. (2011). Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA, 306(14), 1549-1556. https://doi.org/10.1001/jama.2011.1437

13. Hurwitz, B. E., Klaus, J. R., Llabre, M. M., Gonzalez, A., Lawrence, P. J., Maher, K. J., … & Schneiderman, N. (2007). Suppression of human immunodeficiency virus type 1 viral load with selenium supplementation: a randomized controlled trial. Archives of Internal Medicine, 167(2), 148-154. https://doi.org/10.1001/archinte.167.2.148

14. Rayman, M. P., & Stranges, S. (2013). Epidemiology of selenium and type 2 diabetes: can we make sense of it?. Free Radical Biology and Medicine, 65, 1557-1564. https://doi.org/10.1016/j.freeradbiomed.2013.04.003

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