The Tolerable Upper Intake Level (UL)
Selenium is a vital trace mineral important for metabolism and thyroid function. The Tolerable Upper Intake Level (UL) for adults over 19 is 400 micrograms (mcg) per day, encompassing intake from food, beverages, and supplements. Consistently exceeding this limit can lead to selenium toxicity, known as selenosis.
What is Selenium Toxicity (Selenosis)?
Selenosis occurs when selenium levels in the body are excessively high. Acute toxicity from a single large dose is rare but severe, potentially causing gastrointestinal and neurological symptoms, and in extreme cases, organ failure and death. Chronic toxicity, from long-term high intake, is more common and has progressive symptoms.
Symptoms of Excessive Selenium Intake
Excessive selenium intake can cause a 'garlic breath' odor and a metallic taste. Early symptoms include gastrointestinal issues like nausea and diarrhea, fatigue, and irritability. As toxicity progresses, more noticeable symptoms like hair loss and brittle nails can occur. Other symptoms include skin rashes and nervous system issues like peripheral neuropathy and tremors.
Major Causes of Selenium Overload
Over-consuming selenium from food alone is difficult for most people; the main risks come from supplements and very high-selenium foods.
Brazil Nuts and Selenium Intake
Brazil nuts are particularly high in selenium, with one nut potentially containing 68-91 mcg. Eating multiple Brazil nuts regularly can easily exceed the daily UL, especially if also taking supplements. Limiting Brazil nuts to one or two per day is recommended.
Dangers of Supplement Overuse
Supplements are a common cause of overdose. Taking more than 200 mcg of selenium from supplements long-term increases risk. There have also been incidents of misformulated supplements containing dangerously high levels.
The Dangers of Long-Term High Intake
Chronic high selenium intake has been linked to potential long-term health issues. Daily intake over 400 mcg has been associated with an increased risk of type 2 diabetes. Some studies also suggest a link between high selenium levels and an increased risk of squamous cell carcinoma, a type of skin cancer, particularly in those with a history of the condition.
Who is at Higher Risk?
Individuals with kidney problems may have difficulty excreting excess selenium, leading to accumulation. People with autoimmune diseases should also be cautious, as selenium can stimulate the immune system, potentially worsening their condition.
Comparison of Selenium Sources
| Source | Typical Selenium Content | Risk of Overdose | Comment |
|---|---|---|---|
| Brazil Nuts | Very High (68-91 mcg per nut) | High | Easy to exceed UL with regular consumption. |
| Supplements | Variable (often 50-200 mcg/pill) | Medium to High | Misformulation and excessive dosage are common risks. |
| Food (e.g., Seafood) | Moderate (e.g., Tuna: 92 mcg per 3 oz) | Very Low | Risk is extremely minimal when consuming through balanced diet. |
| Soil/Water | Variable | Medium | Risks exist primarily in regions with seleniferous soil. |
How to Avoid Taking Too Much Selenium
Avoiding selenium toxicity involves awareness and moderation:
- Prioritize Food Sources: A balanced diet generally provides enough selenium.
- Limit Brazil Nuts: Consume only one or two per day.
- Use Supplements Cautiously: Stick to recommended doses and consult a doctor before taking high-dose supplements.
- Consult a Professional: Talk to a doctor or dietitian if you have concerns or are considering supplements.
- Check Ingredients: Be aware of selenium content in multi-ingredient supplements.
Conclusion: Moderation is Key
Taking too much selenium in a day is possible, with risks ranging from mild symptoms to severe health issues. The UL of 400 mcg for adults is a crucial limit. While food sources are generally safe, supplements and excessive Brazil nut consumption pose the highest risk of overdose. By being mindful of total intake and favoring dietary sources, most individuals can maintain healthy selenium levels. Consulting a healthcare professional can provide guidance for safe intake.
