What Is Selenium?
Selenium is an essential trace mineral that is crucial for various bodily functions, including metabolism, immune function, and reproductive health. It acts as a powerful antioxidant, helping to protect cells from damage caused by free radicals. Most people get sufficient selenium from their diet through foods like Brazil nuts, seafood, meat, eggs, and whole grains. The concentration of selenium in plant-based foods can vary significantly depending on the soil content where they were grown. While crucial for health, there is a narrow safety margin for selenium, and excessive intake can lead to toxicity. Therefore, understanding who cannot take selenium is vital for avoiding negative health outcomes.
Medical Conditions and Health Concerns
Certain pre-existing health conditions can be exacerbated by selenium supplementation, making it unsafe for some individuals without medical guidance. These conditions include:
- Autoimmune diseases: Conditions such as multiple sclerosis (MS), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA) can be worsened by selenium supplements because the mineral might stimulate the immune system. Individuals with these diseases should generally avoid selenium supplementation unless directed by a doctor.
- Hypothyroidism and iodine deficiency: Selenium is important for proper thyroid function, but supplementing it without addressing an underlying iodine deficiency can actually worsen the condition. Patients with an underactive thyroid should only take selenium supplements under a doctor's supervision, and often in combination with iodine.
- Kidney disease: Individuals with kidney disease or those on dialysis are at a higher risk of complications from selenium supplementation. The kidneys regulate mineral levels in the body, and impairment can lead to high selenium levels and toxicity. Although some patients on hemodialysis may have low selenium, supplementation must be managed carefully by a healthcare provider.
- History of skin cancer: Long-term use of selenium supplements, particularly in higher doses, has been linked to a slightly increased risk of certain skin cancers, specifically squamous cell carcinoma. People with a history of nonmelanoma skin cancer should avoid long-term selenium supplementation.
- Diabetes and prediabetes: Some long-term studies have shown that individuals with a high selenium intake or long-term supplementation have an increased risk of developing type 2 diabetes. Individuals with diabetes should discuss their selenium intake with a doctor, as high levels can be a concern.
Medication Interactions
Selenium can interfere with the effectiveness or increase the side effects of several medications. It is essential to inform a healthcare provider about all medications before starting a supplement, especially if taking:
- Blood-thinning medications: Since selenium can slow blood clotting, taking it with anticoagulants like warfarin (Coumadin) or antiplatelet drugs like aspirin can increase the risk of bruising and bleeding. It should be stopped at least two weeks before any scheduled surgery.
- Immunosuppressants: As selenium can stimulate the immune system, it may counteract the effects of medications designed to suppress the immune system, such as those used after an organ transplant.
- Cholesterol-lowering medications (Statins): Taking selenium with certain antioxidant vitamins (like C and E) might decrease the effectiveness of some statin drugs. However, whether selenium alone has this effect is unclear.
- Chemotherapy drugs: Some chemotherapy agents, such as cisplatin, can lower selenium levels in the body. While supplementation can sometimes help with side effects, it may also decrease the drug's effectiveness.
- Antacids and other medications affecting absorption: Medications that reduce stomach acid, such as proton pump inhibitors, might reduce the body's absorption of selenium.
Toxicity and High Intake Risks
Even in otherwise healthy individuals, high doses of selenium can be toxic. The tolerable upper intake level (UL) for adults is 400 micrograms (mcg) per day, including intake from all sources. Long-term intake above this level increases the risk of selenosis, or selenium toxicity. Brazil nuts are a potent source of selenium and can easily cause a person to exceed the UL if consumed in excess.
Symptoms of selenosis include:
- Garlic-like breath odor
- Metallic taste in the mouth
- Hair loss and brittle nails
- Nausea, vomiting, and diarrhea
- Fatigue and irritability
- In more severe cases, tremors, kidney failure, heart problems, and nervous system issues can occur.
Selenium Supplementation: Safe vs. Cautionary
| Aspect | Generally Safe Intake | Requires Caution/Avoidance | Recommended Action |
|---|---|---|---|
| Source | Foods grown in selenium-sufficient soil | Brazil nuts (high potency), prolonged high-dose supplements | Rely on a balanced diet; monitor intake of high-selenium foods. |
| Health Status | Generally healthy individuals with no known deficiencies or conditions | Autoimmune disease, hypothyroidism, kidney disease, certain cancers | Consult a healthcare provider before use. |
| Medications | No interacting drugs (always verify) | Blood thinners, immunosuppressants, statins, chemotherapy | Discuss with a doctor; avoid during surgery. |
| Dosage | Within Recommended Dietary Allowance (RDA); up to 400mcg short-term | Routinely exceeding 400mcg per day, long-term high doses | Monitor all sources; prioritize dietary intake over supplements. |
Conclusion
While selenium is an essential mineral with many health benefits, it is not safe for everyone, especially in supplemental form. Key populations who should be particularly cautious include those with autoimmune diseases, individuals with hypothyroidism and iodine deficiency, patients with kidney disease, and anyone with a history of nonmelanoma skin cancer. Furthermore, because of its potential for toxicity and interactions with common medications, consulting a healthcare professional is crucial before beginning any selenium supplementation. A balanced diet, rather than supplements, is the safest way for most people to maintain healthy selenium levels.
For further information on selenium, consider reviewing the NIH's detailed consumer factsheet.
