Is it safe to take selenium supplements daily? Understanding the Risks and Benefits

October 13, 2025 •

4 min read

According to the National Institutes of Health, the Tolerable Upper Intake Level (UL) for adults for selenium is 400 micrograms (mcg) per day from all sources, including food and supplements. While a daily intake below this threshold is generally considered safe, understanding the balance is crucial, as taking selenium supplements daily can pose risks if not managed properly.

Quick Summary

Daily selenium intake is generally considered safe below the 400 mcg upper limit, but can cause toxicity if that level is exceeded. Most people with a balanced diet do not need supplements. Long-term or high intake carries risks like selenosis, hair loss, and an increased risk of certain health conditions.

Key Points

Moderate Intake is Key: The Tolerable Upper Intake Level (UL) for selenium is 400 mcg per day for adults, and it is crucial not to exceed this maximum limit from all sources, including supplements.
Toxicity is a Real Risk: Long-term, high intake, particularly from supplementation, can lead to selenosis, causing symptoms like hair loss, nail brittleness, and a garlic-like breath odor.
Diet First: Most people get enough selenium from food and do not require supplements. Food sources like Brazil nuts, seafood, and meat are generally safer and more balanced.
Consult a Professional: Always speak with a healthcare provider before starting daily selenium supplementation to assess your needs, especially if you have pre-existing conditions or take other medications.
Beware of Drug Interactions: Selenium can interfere with medications, including blood thinners, statins, and chemotherapy drugs, requiring careful management.
Deficiency vs. Excess: Both too little and too much selenium can cause negative health effects, a concept known as the U-shaped curve of health outcomes related to nutrient status.

What is Selenium and Why is it Important?

Selenium is an essential trace mineral that plays a vital role in many bodily functions, primarily through its incorporation into proteins called selenoproteins. These selenoproteins act as powerful antioxidants, helping to protect cells from damage caused by free radicals. Beyond its antioxidant properties, selenium is crucial for proper thyroid hormone metabolism, immune system function, and reproductive health.

Because the human body cannot produce selenium, it must be obtained through diet. The amount of selenium in plant-based foods, such as grains and vegetables, depends heavily on the mineral content of the soil where they are grown. In areas with selenium-rich soil, dietary intake is typically sufficient, making routine supplementation unnecessary for most people. Conversely, those living in regions with low-selenium soil may be at a higher risk of deficiency.

Is it Safe to Take Selenium Supplements Daily?

For healthy adults, daily selenium intake, whether from diet or supplements, is generally considered safe as long as the total intake from all sources does not exceed the Tolerable Upper Intake Level (UL) of 400 mcg per day. However, this is a maximum limit, not a target. Most adults in developed countries already meet or exceed the Recommended Dietary Allowance (RDA) of 55 mcg per day through their regular diet alone, meaning supplementation may be redundant.

The primary danger with daily supplementation comes from the potential for excessive intake and the development of selenium toxicity, known as selenosis. Because the therapeutic range for selenium is narrow, it is easier to reach toxic levels than with many other vitamins or minerals. Before starting a daily supplement, it is best to consult a healthcare provider to assess your existing selenium levels and determine if supplementation is truly necessary.

The U-Shaped Curve: Deficiency vs. Toxicity

The relationship between selenium intake and health follows a U-shaped curve. Both inadequate and excessive levels are linked to negative health outcomes. At the bottom of the curve, optimal health is achieved with balanced selenium levels. Moving down either side of the curve, health risks increase:

Low Selenium (Deficiency): Can lead to thyroid dysfunction, impaired immune response, muscle weakness, and reproductive issues. It is also associated with certain regional diseases like Keshan disease.
High Selenium (Toxicity/Selenosis): Results from excessive intake, causing a range of symptoms from mild to severe, including:
- Hair loss and brittle nails
- Gastrointestinal upset (nausea, diarrhea)
- A garlic-like odor on the breath or sweat
- Fatigue and irritability
- Neurological problems
- In extreme cases, high intake can lead to kidney failure, heart attack, or death.

Comparison: Selenium from Food vs. Supplements

It is important to consider the source of your selenium intake. Here is a comparison of obtaining selenium from dietary sources versus supplements:


Feature	Dietary Selenium (from Food)	Supplement Selenium
Safety Margin	Wider, less risk of toxicity as it's difficult to reach harmful levels through diet alone.	Narrower, easy to exceed the 400 mcg UL, increasing risk of selenosis.
Bioavailability	High, as it comes naturally incorporated into food matrices like selenomethionine.	Varies by form (e.g., selenomethionine vs. sodium selenite), but generally well-absorbed.
Monitoring	No active monitoring usually needed unless deficiency risk factors are present.	Recommended to consult a doctor, especially for long-term use, to monitor blood levels.
Interactions	Fewer, as food intake is gradual and balanced.	Higher risk of interactions with other minerals (zinc, calcium) and certain medications.
Primary Use	Maintaining optimal health in most populations.	Correcting a diagnosed deficiency or managing specific medical conditions under supervision.

Important Drug Interactions and Long-Term Risks

Long-term, high selenium intake, particularly from supplementation, has been linked to increased risks of certain health conditions. Studies suggest that high selenium intake over many years may increase the risk of developing type 2 diabetes. Furthermore, some studies have shown mixed results regarding cancer risks, with some indicating that supplementation might increase the risk of certain nonmelanoma skin cancers.

Selenium can also interact with several medications, potentially altering their effectiveness or increasing side effects. These include:

Anticoagulants/Antiplatelet Drugs: May increase the risk of bleeding.
Cholesterol-Lowering Statins: May interfere with the cholesterol-improving effects of some statins.
Immunosuppressants: May decrease their effectiveness by stimulating the immune system.
Chemotherapy Drugs: May decrease the effectiveness of some chemotherapy agents like cisplatin.

How to Get Enough Selenium Safely

For most people, a balanced diet is the safest and most effective way to meet daily selenium needs. The best food sources include:

Brazil Nuts: Extremely high in selenium; consuming just one or two per day can provide a significant amount.
Seafood: Tuna, halibut, and sardines are excellent sources.
Meats: Beef, pork, and poultry provide significant amounts.
Dairy Products: Milk and yogurt contain selenium.
Whole Grains: Oats and whole-wheat bread can contribute to intake.

When to Consider Supplementation

Supplementation should be considered only under the guidance of a healthcare professional, especially for individuals at a higher risk of deficiency. These groups include:

Those with gastrointestinal disorders like Crohn's disease that impair nutrient absorption.
Individuals in regions with known low-selenium soil content and limited dietary access.
Patients on total parenteral nutrition (TPN) without sufficient selenium added to their formula.

Conclusion

While selenium is an indispensable nutrient, the question “Is it safe to take selenium supplements daily?” is highly dependent on individual circumstances. For the average healthy person, obtaining sufficient selenium from a varied diet is a safer strategy than daily supplementation, which carries a risk of reaching toxic levels over time. Selenium supplements are most beneficial for those with a confirmed deficiency or specific medical conditions, and should always be taken under a doctor's supervision. Moderation and informed decisions are key to reaping the benefits of this vital mineral without the dangers of overconsumption.

NIH Office of Dietary Supplements: Selenium

Frequently Asked Questions

Initial signs of excess selenium, or selenosis, often include a garlic-like odor on the breath, a metallic taste in the mouth, hair loss, and brittle or discolored nails.

The Recommended Dietary Allowance (RDA) for most adults is 55 micrograms (mcg) per day. The Tolerable Upper Intake Level (UL) is 400 mcg per day, and this combined total from food and supplements should not be exceeded.

Yes, most people can get a sufficient amount of selenium from a balanced diet. Excellent sources include Brazil nuts, seafood, poultry, meat, and whole grains.

Individuals with sufficient dietary selenium intake, those with autoimmune diseases, people who have had certain skin cancers, and those on specific medications should avoid daily supplementation unless advised by a healthcare provider.

Yes, selenium can interact with a number of medications, including blood thinners (like warfarin), statins, and some antibiotics. It is essential to discuss supplementation with a doctor if you take other drugs.

Long-term daily intake, especially at high levels, can increase the risk of serious health problems, including type 2 diabetes and nerve damage (peripheral neuropathy).

Yes, the amount of selenium in food, especially plant-based food, can vary widely depending on the selenium concentration of the soil where it was grown.