Who Should Not Use Selenium Supplements?

November 20, 2025 •

4 min read

Health experts report that while selenium is a vital trace mineral, its safe intake range is narrow, making excessive use potentially dangerous. This means that for certain individuals and those with specific health conditions, taking selenium supplements can pose significant risks and should be avoided or approached with extreme caution.

Quick Summary

Certain individuals, including those with autoimmune disorders, a history of skin cancer, or specific thyroid issues, should avoid or consult a doctor before using selenium supplements. Risks like toxicity (selenosis) and adverse medication interactions are significant concerns, underscoring the importance of safe usage. Knowing the contraindications is crucial for preventing negative health outcomes.

Key Points

Autoimmune Conditions: People with autoimmune diseases like RA or lupus should avoid selenium supplements, which can overstimulate the immune system.
Skin Cancer History: Individuals with a history of non-melanoma skin cancer should avoid long-term selenium supplementation, as high doses may increase recurrence risk.
Pre-Surgery Precautions: Stop using selenium supplements at least two weeks before any scheduled surgery due to its blood-thinning effects.
Hypothyroidism: Those with an underactive thyroid and iodine deficiency should not take selenium supplements without medical guidance, as it could worsen their condition.
Selenosis Risk: Excessive intake, often from high-dose supplements or too many Brazil nuts, can cause toxicity with symptoms like hair loss and nail changes.
Medication Interactions: Selenium can negatively interact with several medications, including blood thinners, immunosuppressants, and certain chemotherapy drugs.
Balanced Diet Over Supplements: For most people, getting selenium from a balanced diet is safer than supplementation due to the narrow therapeutic-to-toxic window.

Key Groups Who Should Not Use Selenium

While selenium is an essential mineral for proper immune and thyroid function, among other things, a 'one-size-fits-all' approach to supplementation is inappropriate. High doses, especially over a long period, can be toxic and exacerbate certain pre-existing health conditions. It is crucial to understand who falls into a high-risk category.

Individuals with Autoimmune Diseases

For people with autoimmune conditions such as multiple sclerosis (MS), systemic lupus erythematosus (SLE), or rheumatoid arthritis (RA), selenium supplementation is often discouraged. The concern is that selenium may stimulate the immune system, potentially worsening the symptoms associated with these conditions. Any decision to use selenium in these cases must be made in close consultation with a healthcare provider who can weigh the potential benefits against the risks of immune system modulation.

People with a History of Skin Cancer

Long-term use of high-dose selenium supplements has been linked to an increased risk of developing squamous cell carcinoma, a type of non-melanoma skin cancer. For individuals with a history of non-melanoma skin cancer, or those at high risk for it, avoiding long-term supplementation is a critical precaution. Studies have shown that while some forms of cancer may be reduced by optimal selenium levels, excessive amounts can have the opposite effect on certain types.

Those with Underactive Thyroid (Hypothyroidism)

While selenium is vital for thyroid hormone metabolism, taking supplements can be problematic for people with hypothyroidism, particularly if they are also iodine-deficient. In such cases, taking selenium alone can worsen the condition. These individuals should only consider supplementation under strict medical supervision and, if necessary, in combination with iodine, as directed by their doctor.

Patients Undergoing Surgery

Selenium possesses blood-thinning properties, which can increase the risk of bleeding both during and after a surgical procedure. For this reason, individuals scheduled for surgery should stop taking selenium supplements at least two weeks beforehand to minimize any risks.

Risks of Selenium Toxicity (Selenosis)

An overdose of selenium, known as selenosis, can occur from excessive consumption through supplements or high-selenium foods like Brazil nuts. The tolerable upper intake level (UL) for adults is 400 mcg daily; consistently exceeding this limit increases toxicity risk.

Common signs of selenosis include:

A metallic taste in the mouth
Garlic-like breath odor
Brittle or lost hair and nails
Gastrointestinal upset, including nausea and diarrhea
Skin rashes and lesions
Fatigue and irritability
In severe cases, neurological symptoms and organ failure

Comparison of Safe vs. Risky Selenium Intake


Feature	Safe Selenium Intake	Risky Selenium Intake
Source	Whole foods like fish, eggs, poultry, and grains grown in selenium-rich soil.	High-dose supplements or overconsumption of extremely selenium-rich foods like Brazil nuts.
Dosage	Within the Recommended Dietary Allowance (RDA) of 55 mcg per day for adults.	Consistently exceeding the Tolerable Upper Intake Level (UL) of 400 mcg daily.
Application	Correcting medically diagnosed selenium deficiency.	Self-medicating or using for unproven health benefits, especially with high doses.
Health Status	Generally healthy individuals.	People with autoimmune conditions, hypothyroidism, or kidney disease.
Side Effects	Typically none, when consumed within recommended guidelines.	Can cause severe toxicity, including hair loss, nerve damage, and nausea.

Medication Interactions to Consider

Selenium can interfere with various medications, affecting their efficacy or increasing the risk of side effects.

Key drug interactions include:

Anticoagulants/Antiplatelet Drugs: Selenium may increase the risk of bruising and bleeding when taken with blood-thinning medications such as warfarin.
Immunosuppressants: As selenium can stimulate immune activity, it may decrease the effects of drugs designed to suppress the immune system, such as those used post-organ transplant.
Chemotherapy Drugs: Certain chemotherapy agents, like cisplatin, can be impacted by selenium levels, though the exact effect is still under investigation.
Cholesterol-Lowering Statins: The effectiveness of some statin drugs, particularly when combined with niacin, can be decreased by high doses of selenium.
Birth Control Pills: Oral contraceptives may increase blood levels of selenium, requiring careful monitoring.

Conclusion

While selenium is an essential nutrient for many bodily functions, it is not safe for everyone, and its use requires careful consideration, especially in supplement form. Certain individuals, such as those with autoimmune disorders, a history of skin cancer, or specific thyroid problems, face increased risks and should consult a healthcare professional before considering supplementation. The narrow safety margin for selenium means that excess intake can lead to serious toxicity, and interactions with common medications are also a concern. A balanced diet rich in selenium-containing foods is the safest approach for most people. Anyone considering a selenium supplement should have their levels checked and discuss their medical history and current medications with a doctor to determine if it is appropriate for them.

For more detailed information on nutrient safety and interactions, the National Institutes of Health Office of Dietary Supplements is an excellent resource(https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/).

Frequently Asked Questions

While it's difficult to get too much selenium from food alone, overconsumption of certain foods, most notably Brazil nuts, can lead to toxicity (selenosis). Just one Brazil nut can contain more than the daily recommended amount.

Selenosis, or selenium toxicity, is a risk for individuals who take high-dose supplements, live in areas with high selenium soil and eat local produce, or over-consume selenium-rich foods like Brazil nuts. Toxicity symptoms include hair loss, brittle nails, and gastrointestinal issues.

Yes, selenium can slow blood clotting. Taking selenium supplements alongside anticoagulant or antiplatelet drugs, such as warfarin, can increase the risk of bleeding and bruising.

People with autoimmune diseases like multiple sclerosis, rheumatoid arthritis, or lupus should avoid selenium supplements. Selenium may stimulate the immune system, potentially aggravating symptoms.

If you have an underactive thyroid (hypothyroidism), particularly with a co-existing iodine deficiency, taking selenium supplements can potentially worsen the condition. Always discuss supplementation with your doctor if you are on thyroid medication.

Early signs of a selenium overdose often include a garlic-like odor on the breath, a metallic taste in the mouth, nausea, diarrhea, and fatigue.

Selenium is possibly safe during pregnancy in amounts not exceeding 400 mcg daily for a short term, but doses higher than this are considered unsafe due to toxicity risks. Pregnant women should consult their healthcare provider before taking any supplements.

Long-term use of high-dose selenium supplements may increase the risk of certain types of non-melanoma skin cancer, specifically squamous cell carcinoma. Those with a history of skin cancer should avoid long-term supplementation.