Selenium Supplement Guide

Our assessment

The evidence shows that selenium is a critical mineral for your body, particularly for thyroid function and antioxidant defense. Our assessment is that for most people, a balanced diet provides adequate selenium, and supplementation should be approached with caution. The data confirms that getting too much selenium over time can be harmful NIH ODS ↗.

How it works

Think of selenium as a key worker in several essential processes. It supports your thyroid by helping produce and convert thyroid hormones, which regulate your metabolism. It also acts as a powerful antioxidant, neutralizing free radicals and reducing oxidative stress by upregulating your body's own antioxidant enzymes NIH ODS ↗.

Safety profile

FDA received 9,847 total adverse event reports for this product. The safety data is clear: excessive selenium intake over time can cause harm. Specific side effects include garlic breath, a metallic taste in the mouth, hair loss, and brittle nails or nail loss NIH ODS ↗ FDA FAERS ↗. Be aware that Brazil nuts contain very high amounts of selenium (68–91 mcg per nut) and can push you over the upper limit if you eat too many NIH ODS ↗. Selenium may also interact with the chemotherapy drug cisplatin, which can lower your selenium levels NIH ODS ↗.

Our recommendation

Start by evaluating your diet before considering a supplement. If you eat a varied diet, you likely get enough selenium. If you do supplement, avoid exceeding the upper limit and be mindful of other sources like Brazil nuts. Always consult your doctor before starting selenium, especially if you are undergoing chemotherapy NIH ODS ↗.