Selenium supports thyroid function, immunity, antioxidant defense, heart health, and fertility. The recommended daily intake is 55 mcg for adults, while the upper limit is 400 mcg/day. However, excess intake can cause hair loss, brittle nails, nausea, fatigue, nerve damage, and selenium toxicity.
Table of Contents
Health Benefits
Selenium is a crucial micronutrient for overall health, influencing metabolism, weight loss, body composition, athletic performance, cardiovascular function, cognitive health, skin appearance, and longevity.
Cellular Protection
Selenium is a critical trace mineral that acts as a powerful antioxidant in the body, primarily through its role in glutathione peroxidase enzymes. These enzymes protect cells from oxidative stress, which can lead to DNA damage, inflammation, and chronic diseases.
By neutralizing free radicals, selenium reduces the risk of premature aging, neurodegenerative disorders, and cardiovascular diseases.
Boosts Immune System Function
Selenium is essential for a well-functioning immune system. It enhances the production of white blood cells, supports T-cell function, and regulates inflammatory responses.
This helps the body defend against infections, viruses, and chronic illnesses, including autoimmune diseases. Research suggests that selenium deficiency may increase susceptibility to infections, while adequate intake improves recovery rates.[1]
Supports Thyroid Health and Metabolism
The thyroid gland relies heavily on selenium to produce and regulate thyroid hormones. These hormones play a crucial role in metabolism, energy production, and body temperature regulation.[2,3]
Selenium helps convert inactive T4 hormone into the active T3 hormone, optimizing metabolic efficiency. A well-functioning thyroid is essential for weight management, energy levels, and overall hormonal balance.
If you have thyroid disease, it’s important to discuss your selenium and iodine levels with your doctor.
Enhances Weight Loss
By improving thyroid function and metabolism, selenium contributes to effective weight management. A well-functioning metabolism burns more calories at rest, making it easier to maintain a healthy body weight.
Additionally, selenium’s role in reducing oxidative stress helps decrease inflammation, which is often linked to obesity and metabolic disorders. Individuals with sufficient selenium levels are more likely to have balanced energy levels and improved fat oxidation.
Sports Performance
Selenium plays a vital role in muscle function and recovery. It supports protein synthesis, reduces muscle damage from oxidative stress, and enhances endurance.
Athletes and active individuals benefit from selenium’s ability to improve mitochondrial efficiency, allowing muscles to produce energy more effectively. It also aids in post-exercise recovery by reducing muscle soreness and inflammation.
Cardiovascular Health
Selenium helps maintain heart health by preventing oxidative damage to blood vessels and reducing inflammation. It also plays a role in regulating cholesterol levels and preventing the buildup of arterial plaque.
Some studies suggest that selenium lowers the risk of heart disease by improving blood vessel function and reducing the risk of stroke.[4,5]
Skin, Hair & Nail Health
As a potent antioxidant, selenium protects skin cells from damage caused by UV radiation, pollution, and environmental toxins. It helps prevent premature aging, reduces wrinkles, and promotes a clear complexion.[6,7]
Selenium also strengthens hair follicles, preventing hair loss and enhancing hair growth. Additionally, it supports healthy nail growth by preventing brittleness and breakage.[8,9]
Brain Health
Adequate selenium intake is linked to a lower risk of neurodegenerative diseases like Alzheimer’s and Parkinson’s. The brain is highly susceptible to oxidative damage, and selenium helps protect neurons from deterioration. It also plays a role in mood regulation, reducing symptoms of depression and anxiety.[10,11]
Longevity
Selenium’s role in reducing inflammation, oxidative stress, and cellular damage contributes to longevity. Higher selenium levels are associated with a lower risk of cancer, cardiovascular diseases, and autoimmune conditions.
It also supports detoxification processes in the liver, helping the body eliminate harmful toxins.
Regulates Hormonal Balance & Fertility
Selenium is essential for reproductive health in both men and women. It improves sperm quality, motility, and testosterone levels in men, while supporting egg health and hormonal balance in women.
It also helps regulate estrogen levels, reducing the risk of hormonal imbalances that can lead to weight gain, mood disorders, and reproductive issues.
Daily Value
Selenium requirements vary based on age, gender, and physiological conditions such as pregnancy, lactation, or intense physical activity. The recommended daily intake (RDI) is measured in micrograms (mcg) per day. Below is a breakdown of selenium intake recommendations for different groups:
| Group | Recommended Daily Intake (mcg/day) |
|---|---|
| Infants (0–6 months) | 15 |
| Infants (7–12 months) | 20 |
| Children (1–3 years) | 20 |
| Children (4–8 years) | 30 |
| Children (9–13 years) | 40 |
| Teens (14–18 years) | 55 |
| Adult Men (19+ years) | 55 |
| Adult Women (19+ years) | 55 |
| Pregnant Women | 60 |
| Lactating Women | 70 |
| Seniors (65+ years) | 55 |
| Athletes | 60–100 |
Recommended Daily Intake for Selenium.
Scientists found that a selenium dose of 1.6 mcg per kilogram (0.72 mcg per pound) is good for improving insulin sensitivity. So, a daily selenium dose of 140 mcg for men and 110 mcg for women seems ideal for preventing insulin resistance and obesity! Οther studies have shown that a daily selenium dose of 100-150 mcg a day is beneficial against cancer.[12]
According to the famous CODING study, obesity is associated with low dietary selenium intake. Every increase of 1 mcg of selenium per kilogram causes 3–6% decrease in the proportion of body fat mass! Participants who received a selenium supplementation of 240 mcg a day lost more fat.[13]
Most people who follow a balanced diet can obtain enough selenium from food. However, selenium levels in food depend largely on the soil where crops are grown and the dietary choices people make. Some regions have selenium-poor soil, leading to lower dietary intake.
Foods rich in selenium include Brazil nuts (the highest natural source), seafood, organ meats, eggs, poultry, whole grains, dairy, and certain seeds.
However, processed foods generally contain little to no selenium, which is a concern in modern diets.
Modern American Diet
The typical American diet is highly processed and low in whole, nutrient-dense foods. Many people consume excessive amounts of refined grains, fast food, and packaged snacks, which are poor sources of selenium.
Additionally, factory-farmed meats and vegetables grown in depleted soils may have lower selenium content than their organic or traditionally farmed counterparts.
While some Americans meet their selenium needs, those with poor diets or living in selenium-deficient soil regions (such as parts of the Midwest and Northeast) may not.
Traditional Mediterranean Diet
The Mediterranean diet, which emphasizes whole foods, olive oil, fish, nuts, legumes, and whole grains, generally provides adequate selenium.
Seafood, a common part of the Mediterranean diet, is a good source of selenium.
Additionally, whole grains and dairy contribute to selenium intake.
However, selenium content in Mediterranean-grown plants varies based on soil quality, and strict vegetarians or vegans following this diet may need to ensure they get enough selenium from nuts (especially Brazil nuts), seeds, and whole grains.
Who might be at Risk for Selenium Deficiency?
- People living in selenium-poor soil regions (such as some parts of Europe, China, and the northeastern U.S.).
- Vegetarians and vegans who do not consume selenium-rich animal products.
- Individuals on restrictive or highly processed diets.
- People with digestive disorders like Crohn’s disease or celiac disease, which impair nutrient absorption.
- Pregnant and lactating women, as they have increased selenium needs.
- Athletes, who may require more selenium due to increased oxidative stress from intense physical activity.
Foods rich in Selenium
To naturally increase your selenium intake, focus on foods rich in this essential mineral. The best sources include Brazil nuts, seafood, meats, eggs, and whole grains.
| Food | Serving Size | Selenium Content (mcg) | % of Daily Needs (55 mcg) |
|---|---|---|---|
| Brazil nuts | 1 nut (5g) | 68–91 mcg | 124–165% |
| Yellowfin tuna | 85g (3 oz) | 92 mcg | 167% |
| Sardines (canned) | 85g (3 oz) | 45 mcg | 82% |
| Salmon | 85g (3 oz) | 40 mcg | 73% |
| Shrimp | 85g (3 oz) | 34 mcg | 62% |
| Turkey (cooked) | 85g (3 oz) | 31 mcg | 56% |
| Chicken breast | 85g (3 oz) | 22 mcg | 40% |
| Beef (cooked) | 85g (3 oz) | 33 mcg | 60% |
| Eggs | 1 large | 15 mcg | 27% |
| Cottage cheese | ½ cup | 11 mcg | 20% |
| Sunflower seeds | 28g (1 oz) | 19 mcg | 35% |
| Brown rice | 1 cup (cooked) | 19 mcg | 35% |
| Whole wheat bread | 1 slice | 13 mcg | 24% |
| Mushrooms | 100g | 12 mcg | 22% |
| Lentils | 1 cup (cooked) | 6 mcg | 11% |
| Spinach | 1 cup (cooked) | 5 mcg | 9% |
Brazil nuts are the richest source, but eat only 1-2 nuts per day to avoid excessive selenium intake.
Should I take Selenium Supplements?
If you don’t eat Brazil nuts or seafood—two of the richest natural sources of selenium—you might be at risk of insufficient selenium intake, depending on the rest of your diet.
If you consume a well-balanced diet with enough selenium-containing foods, you might not need a supplement. However, if your diet is limited or if you live in an area with selenium-poor soil (such as parts of Europe and China), supplementation may be beneficial.
When Are Selenium Supplements Especially Beneficial?
Selenium supplements can be particularly useful in specific situations:
- People with Low Selenium Intake – Those who avoid selenium-rich foods or live in areas with poor soil selenium levels.
- Thyroid Health – Selenium is crucial for thyroid hormone production and may help with Hashimoto’s thyroiditis or mild hypothyroidism.
- Immune Support – It plays a role in immune function and may support recovery from infections.
- Antioxidant Protection – Helps reduce oxidative stress, which can benefit cardiovascular health, skin, and aging.
- Fertility – Selenium is important for sperm quality and overall reproductive health.
- Athletes – Intense exercise increases oxidative stress, and selenium supports antioxidant defense.
- Detoxification – Selenium helps remove heavy metals like mercury from the body.
Which Type of Selenium is Best Absorbed?
The most absorbable and bioavailable forms of selenium are:
- Selenomethionine – A natural organic form found in food, well-absorbed, and retained longer in the body.
- Selenium-enriched yeast – Contains multiple selenium compounds and is effective.
- Sodium selenite or selenate – Inorganic forms, less absorbable but still useful in some cases.
Selenomethionine is often preferred because it mimics natural dietary sources and is more efficiently stored in the body.
What’s the Best Dose?
The recommended daily intake (RDI) for selenium for supplementation is:
- A safe and effective dose is 50–200 mcg per day.
- Do not exceed 400 mcg per day, as excessive selenium can cause toxicity (selenosis).
Cycling selenium: If you take a supplement long-term, consider taking breaks (e.g., 1–2 months off per year) to prevent excessive accumulation.
Should You Take Selenium with Food or on an Empty Stomach?
- Selenium is best absorbed with food, especially protein-containing meals.
- Avoid taking it with high doses of zinc or vitamin C, as they may interfere with absorption.
- It can be taken in the morning or with lunch, but avoid taking it late at night, as it may slightly stimulate metabolism.
If your diet is low in selenium-rich foods and you have symptoms of deficiency (fatigue, hair loss, weak immunity, thyroid dysfunction), a supplement may help. If unsure, a blood test can determine your selenium levels before supplementing long-term. Always consult your health provider before taking any supplementation.
Dosage in Supplements
Most selenium supplements contain 100–200 mcg per serving, which is below the toxicity threshold (400 mcg/day) but may still be too high if combined with dietary selenium.
Some high-dose supplements provide 400 mcg or more per pill, which exceeds the tolerable upper intake level (UL) and increases toxicity risk, especially with long-term use.
Multivitamins often contain 50–100 mcg, so taking them alongside a selenium supplement may lead to excessive intake.
Dangers of Excess Selenium
While selenium is essential for health, too much selenium—whether from supplements or excessive intake of selenium-rich foods like Brazil nuts—can lead to serious short-term and long-term health risks.
Toxicity is most commonly caused by high-dose supplements, but eating large amounts of Brazil nuts regularly can also result in excessive selenium levels.
Selenium Toxicity (Selenosis)
Chronic intake of more than 400 mcg/day can cause selenosis, a condition with symptoms such as:
- Brittle hair and nails, leading to hair loss and nail cracking or falling off.
- Garlic-like breath odor, caused by excess selenium affecting metabolism.
- Skin rashes and irritations, including redness, blisters, and excessive dryness.
- Fatigue, irritability, and mood changes, as selenium affects neurotransmitter function.
- Nausea, diarrhea, or digestive issues, from disrupting gut function.
Increased Risk of Type 2 Diabetes
Excess selenium has been linked to a higher risk of insulin resistance and type 2 diabetes. Some studies suggest that selenium supplementation beyond the recommended intake can impair blood sugar regulation.[14]
Neurological and Cognitive Issues
High selenium levels may negatively impact brain function, leading to symptoms like:
- Memory problems and confusion, especially in older adults.
- Nerve pain (neuropathy), causing tingling, burning, or numbness in extremities.
- Tremors and muscle weakness, due to selenium affecting the nervous system.
Heart and Blood Vessel Problems
Too much selenium can cause:
- High blood pressure, as selenium influences circulation.
- Increased risk of heart disease, possibly due to oxidative stress from excess intake.
- Irregular heartbeat (arrhythmia), which may be dangerous for people with heart conditions.
Bleeding Risks & Surgery Concerns
Selenium affects blood clotting, increasing the risk of excessive bleeding during surgery. High selenium intake can lead to:[15]
- Prolonged bleeding from wounds or gums, making dental procedures riskier.
- Increased risk of internal bleeding, which is especially concerning for seniors, people on blood thinners, or those with clotting disorders.
Risks for Pregnant Women and Babies
- Too much selenium during pregnancy can harm fetal development and may increase the risk of birth defects.
- High selenium levels in breastfeeding mothers can pass into breast milk, potentially harming the infant.
- Selenium imbalance may increase the risk of miscarriage if levels are extremely high.[16]
Thyroid Dysfunction
Selenium is critical for thyroid health, but excessive amounts can:
- Disrupt thyroid hormone production, leading to hypothyroidism or hyperthyroidism.
- Worsen autoimmune thyroid disorders, like Hashimoto’s or Graves’ disease.
Cancer Risk
While selenium is an antioxidant, excess levels may actually increase cancer risk, particularly in the skin, prostate, and lungs, according to some studies.[17]
Who Should Be Extra Cautious?
- Pregnant and breastfeeding women – to avoid fetal complications.
- People with thyroid conditions – as excess selenium can worsen hormone imbalances.
- Diabetics or prediabetics – to prevent worsening insulin resistance.
- Seniors – due to increased risk of cognitive decline and heart issues.
- Patients before surgery – due to bleeding risks.
- People on blood thinners – as selenium can interfere with clotting.
- Those with autoimmune diseases – as excess selenium may worsen inflammation.
How to avoid Selenium Toxicity
- Stick to the recommended daily intake (55 mcg for adults, 60 mcg for pregnant women).
- Limit Brazil nuts to 1-2 nuts per day, as just 4-5 nuts can exceed the safe limit.
- Avoid unnecessary selenium supplements if your diet already includes selenium-rich foods.
- Check multivitamins, as many contain selenium, leading to unintentional overconsumption.
By managing selenium intake properly, you can reap its benefits without the risks of toxicity!