As a trace element, selenium is found in certain foods and reflects the amount of selenium found in the soil where the food is grown. Some areas, such as New Zealand, have low-selenium soil and subsequently higher levels of selenium deficiency in the population. Other areas, such as certain regions in China have high selenium levels which can cause selenium toxicity.[ref]
This article digs into how selenium is used in the body, why it is important, and how genetic variants can make someone more susceptible to problems with a selenium-deficient diet.
Selenoproteins: Using selenium in your cells
The term selenoprotein refers to proteins that interact with selenium. The role of these proteins can be broken down as:
- transport of selenium
- antioxidant/redox related enzymes
- thyroid enzymes
The transport of selenium throughout the body and into cells is important, and it varies a bit due to genetic differences.
The antioxidant usage of selenium is essential for healthy cells. Glutathione peroxidase 1 (GPX1) is used in cells to reduce pro-oxidants, such as hydrogen peroxide. Excessive pro-oxidants can cause cell damage or DNA damage.
The glutathione peroxidase 4 (GXP4) protein includes selenium and is essential for reducing lipid oxidation in cells with oxidative stress. This impacts downstream inflammatory processes including IL-1 and COX2 (cyclooxygenase).[ref]
How much selenium do you need?
The average intake of selenium per day in European countries is between 30 – 60 μg/day. The US RDA is 55 μg/day. Other countries have different standards, ranging from 40 – 85μg/day.[ref] Why the wide range? I don’t know…
Getting more than 400 μg/day of selenium can cause toxicity.[ref]
Selenium is essential to the production of antioxidants:
Oxygen is vital to life, but it is also a very reactive molecule. So the body tightly regulates oxidants – producing antioxidant compounds inside your cells to counteract pro-oxidants.
High levels of pro-oxidants, or ROS, cause oxidative stress in cells. This can lead to DNA damage, possibly causing cancerous mutations. It is essential to have the right balance of oxidants in the cell, and selenoproteins are an important part of the balance.[ref]
In general, increasing the intake of selenium has been shown to increase the activity of glutathione peroxidase 1 (GPx1), an important antioxidant.[ref] Don’t go overboard on selenium, though – read the section on toxicity before supplementing.
Keshan cardiomyopathy is one disease caused by selenium deficiency. This disease causes insufficient cardiac output, resulting in an enlarged heart.[ref]
People with Keshan cardiomyopathy have low selenium concentrations in their blood, causing a lower amount of glutathione peroxidase 1.[ref] Keshan’s disease is named for a region in China where selenium deficiency is very common.
Another disease associated with selenium deficiency is Kashin-Beck disease. The disease causes joint degeneration in children and can cause dwarfism.[ref]
Both of these diseases are thought to be the result of decreased antioxidants (e.g. glutathione peroxidase) due to low selenium status.
Low levels of selenium are also linked to decreased immune function, thyroid problems, hair loss, brain fog, and male infertility.
Selenium and the immune system:
When the immune system is fighting off a viral infection, a lot of reactive oxygen species (ROS) are formed. ROS is important in fighting off the virus, but when it overwhelms the body’s ability to neutralize it, oxidative stress in the cell results.
Specific viruses that trigger excessive oxidative stress include Epstein Barr virus, hepatitis B, RSV, hepatitis C, Ebola, and HIV.[ref]
More recently, research shows that SARS-CoV-2 also increases ROS and interacts with selenoproteins.[ref] Selenium (along with other vitamins and minerals) is important in the body’s viral response.
Additionally, some viruses interact with the selenoproteins (glutathione peroxidase and thioredoxin reductase), reducing the amount of these proteins. Thus, it can be a double-whammy of needing more antioxidants to deal with ROS and at the same time having reduced selenoproteins.
Sufficient selenium is also essential for the prevention of viral replication of certain viruses, such as the coxsackie virus and influenza.[ref]
A recent article in the journal Medical Hypothesis explains that sodium selenite, a specific form of selenium, may help to stop the replication of coronaviruses.[ref]
Selenium and thyroid function:
Thyroid hormones regulate overall metabolism (calories burned), control heartbeat, impact body temperature, increase lung oxygenation, increase the development of muscle fibers, and stimulate bone growth in metabolism.[ref]
While iodine is perhaps the best-known cofactor micronutrient for the thyroid, selenium is also important.
Selenium is essential for the creation of the DIO1 and DIO2 enzymes, which convert between the active and storage forms of thyroid hormones.[ref]
Additionally, selenium in the antioxidant system, especially GPX1, is important in protecting against oxidative stress in the thyroid itself. Hashimoto’s, an autoimmune cause of hypothyroidism, is linked to low selenium.[ref]
Related article: Genetics and thyroid function.
Obesity and selenium status:
Several studies have shown that low selenium status is often found in people with higher BMI. For example, a study in Spain found that overweight children were likely to have serum selenium levels that are 14% lower than normal-weight children. Not all studies agree, though, and there are likely other factors at play also (such as thyroid function).[ref]
More is not always better!
When it comes to selenium, more is not better. Instead, having selenium levels in the middle of the normal range is usually best.
For example, a study of metabolic syndrome found that people with low and high selenium concentrations were more likely to have metabolic syndrome than those in the middle tiers.[ref]
Similarly, men with low or high selenium levels are at an increased risk of prostate cancer.[ref]
Selenium toxicity: Consuming more than 400 mcg/day of selenium is associated with selenium toxicity. Signs of toxicity include fragile hair, fingernail problems.
Selenium in food:
The amount of selenium found in foods is dependent on the type of food and the amount of selenium in the soil. Selenium content of the soil varies throughout the world, depending on the pH of the soil, organic matter, soil composition, agricultural activity, and mining.[ref]
Here is the variation in selenium across US states (USGS map):
Plants are the primary source of selenium in foods for humans and animals. Plants bioaccumulate the selenium from the soil as selenium compounds and convert it to organic selenium. For example, plants can convert selenium from the soil into selenocysteine or selenomethionine, which we are able to absorb and use.
In general, foods that are higher in selenium include Brazil nuts, organ meats such as kidney and liver, cod, salmon, mustard, egg whites, and whole wheat (dependent on soil).[ref]
For animal foods, such as chicken, the selenium content depends on what the animal is eating. For example, selenium is added to poultry feed in some countries.[ref] Judging by the map above, grass-fed beef from the Dakotas or Montana is likely to have more selenium than cattle grazing in New Mexico or Arizona. Most people today eat foods grown in a range of locations, so having a varied diet may help to protect them from selenium deficiency.
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Gene-diet interaction: Genetic variants in the selenoproteins could make you more susceptible to negative outcomes with low selenium levels. These variants could make it more important for you to ensure that you are getting plenty of selenium in your diet.
Some of the studies on selenoproteins point to these variants having no impact on people who have higher selenium levels.[ref]
Variants related to transporting selenium:
SEP15 gene: encodes a selenium transport protein, selenoprotein F
Check your genetic data for rs5845 (23andMe v4; AncestryDNA):
- G/G: typical
- A/G: typical levels
- A/A: lower selenium transport into cells[ref] increased risk of lung cancer in people with lower selenium levels, lower verbal memory scores[ref]
Members: Your genotype for rs5845 is —.
Check your genetic data for rs561104 (23andMe v5; AncestryDNA):
- C/C: higher serum selenium[ref]
- C/T: typical serum selenium
- T/T: typical serum selenium
Members: Your genotype for rs561104 is —.
SEPP1 gene: encodes the selenoprotein P which is a transporter of selenium from the liver to the rest of the body.
Check your genetic data for rs7579 (23andMe v4, v5; AncestryDNA):
- T/T: lower serum selenium levels, increased risk of prostate cancer[ref]
- C/T: lower serum selenium levels
- C/C: typical
Members: Your genotype for rs7579 is —.
Check your genetic data for rs3877899 (AncestryDNA):
Members: Your genotype for rs3877899 is —.
SELENOS gene: encodes selenoprotein S, which protects the endoplasmatic reticulum from stress due to misfolded proteins
Check your genetic data for rs34713741 (23andMe v5; AncestryDNA):
- C/C: typical
- C/T: increased risk of colon and gastric cancers
- T/T: increased risk of colon and gastric cancers[ref][ref]
Members: Your genotype for rs34713741 is —.
Variants related to Selenium in antioxidant production:
GPX4 gene: glutathione protein that depends on selenium as a cofactor. GPX4 is important in reducing oxidized lipids in the cell membrane.
Check your genetic data for rs713041 (AncestryDNA):
- C/C: typical
- C/T: altered GPX4 enzyme, increase risk of colon cancer or breast cancer with low selenium; higher lipid oxidation in situations with oxidative stress
- T/T: altered GPX4 function, increased risk of colon cancer or breast cancer with low selenium; higher lipid oxidation in situations with oxidative stress[ref]
Members: Your genotype for rs713041 is —.
Check your genetic data for rs1050450 Pro198Leu (23andMe v4)
- A/A: lower GPX enzyme activity[ref], increased risk of breast cancer[ref] higher selenium plasma levels, selenium supplementation (or Brazil nut intake) increases GPX1[ref] linked to Keshan disease in people with low selenium levels[ref]
- A/G: lower GPX enzyme activity, increased risk of breast cancer, higher selenium plasma levels;
- G/G: typical enzyme activity; eating Brazil nuts more likely to work for decreasing DNA damage[ref][ref]
Members: Your genotype for rs1050450 is —.
Eat more selenium-rich foods:[ref]
- Brazil nuts (depending on soil selenium)[ref]
- Wheat (depending on soil)
Avoiding toxicants: Selenium is essential in protecting from oxidative stress. Animal studies show that low selenium may not be all that detrimental when the cells aren’t stressed out. Avoiding toxicants that cause oxidative stress is one way to spare your selenium levels. For example, the pesticide paraquat is much more lethal in animals that are selenium deficient.[ref][ref] Glyphosate, the main ingredient in the herbicide Roundup, may also decrease your selenoproteins.[ref]
How to avoid toxicants is the million-dollar question…Eating organic when available may help some. Pesticides around the house and on your pets may also be an important route of exposure. If you live near an agricultural area, drinking water contamination can be a big problem especially in areas where aerial spraying is common.[ref]
Related article: Glyphosate: Interaction with Genetics
Supplemental selenium is readily available at health food stores and online.
Test first: I would highly recommend getting a blood test done first to make sure that you are deficient in selenium before supplementing. Selenium is toxic if you go overboard. Talk with your doctor about getting selenium testing done. If you live in the US, you can order the test yourself through places like Ulta Lab Tests ($54 serum, or part of a micronutrients panel). Shop around on lab tests online – the prices vary a lot.
Related Articles and Genes:
Viruses: Are you susceptible to the coronavirus, flu, and more
Your genetic variants shape your immune system and give you superpowers against some pathogens – and perhaps more susceptible to others.
Detoxification: Phase I and Phase II Metabolism
Your body metabolizes (breaks down) the foreign substances that come into it – and then gets rid of it. This is usually a two or three-stage process.
Thyroid Hormone Levels and Your Genes
Your genes play a big role in how well your thyroid works and how your body produces and converts the different forms of thyroid hormone. Genetic variants can impact your risk for hypothyroidism, Hashimoto’s, and Graves’ disease.