The short answer: selenium is a "just a little" mineral
Selenium is measured in mcg (micrograms — 1/1,000 of a milligram), not mg. That's how little of it you need.
| Benchmark | Daily amount |
|---|---|
| Recommended intake | About 60 mcg |
| Typical supplement amount | 200 mcg or less |
| Upper limit (above this is risky) | 400 mcg |
Side effects of too much selenium
Taking too much selenium can cause:
- Hair loss: Cases have been reported where the structure of the protein in hair (keratin) is disrupted and hair falls out.
- Weak or misshapen nails
- Numbness and tingling in hands and feet: It can affect peripheral nerves (the nerves in your arms and legs).
- Trouble sleeping, low mood: Unexplained sleep problems are often reported in people taking selenium-only supplements.
- Facial flushing, easy bruising or bleeding, muscle pain: These can appear at 1,000 mcg a day or more.
- Liver and kidney strain: Some data show that taking more than 400 mcg a day for a long time led toward liver scarring (cirrhosis).
In a large study (SELECT), people who took 200 mcg every day had about a 7% higher risk of diabetes. The idea that "it's an antioxidant, so more is better" is especially risky with selenium.
What is selenium used for?
Selenium is essential for glutathione peroxidase (an enzyme that clears free radicals), one of the body's main antioxidant enzymes. In simple terms, it's "a must-have part in your body's detox factory."
- Thyroid: It's used to convert thyroid hormone into its active form, and it helps protect thyroid tissue from oxidative damage.
- Antioxidant support: Along with glutathione, it reduces free radicals that "rust" the body. It's sometimes included in liver support formulas.
- Men trying to conceive: Through its antioxidant action, it may help sperm quality and movement.
- Skin: It's also used for skin health through its antioxidant effects.
Who may need it
- □ You're managing an underactive or overactive thyroid (after talking to your doctor)
- □ You have eye changes, like bulging eyes, from an overactive thyroid
- □ You're a man trying to conceive
- □ Your multivitamin has no selenium or very little
Many people with an underactive thyroid say they felt noticeably better after taking selenium with zinc. Some guidelines in the US and Europe suggest trying selenium for about 6 months when an overactive thyroid causes eye symptoms. If you have a thyroid condition, be sure to talk to your doctor before taking it.
Who doesn't need it
- People already taking a multivitamin: Many already contain selenium. Check the label; if you're getting enough, you don't need extra.
- People who eat Brazil nuts often: Just one or two Brazil nuts contain a lot of selenium. Add it into your total along with supplements.
- People concerned about diabetes: A study found that taking 200 mcg or more every day slightly raised diabetes risk.
- People who just want "antioxidants" with no specific reason: Other antioxidant supplements will do the job.
How to take selenium and how to choose it
Bottom line: after meals, 200 mcg a day or less. First, add up the selenium in every product you take.
- Add up the labels — Total the mcg of selenium in your multivitamin, antioxidant blends and thyroid supplements. If it's over 400 mcg, cut back.
- Take it after meals.
- Don't take high doses (400 mcg or more) for a long time. Even if your doctor prescribes it, take a break after 1–3 months.
Here's how to choose a form:
| Type | What it's like | Best for |
|---|---|---|
| Organic selenium (selenomethionine, selenocysteine, selenium yeast) | Absorbs well and is stored in muscle, then released slowly. But because it absorbs so well, it's easier to go over the limit. | General health, thyroid support |
| Inorganic selenium (selenite) | An antioxidant form that acts right away. Absorbs less well. | Special purposes under a doctor's supervision |
Medications and conditions to watch
- Check Multivitamin — Combined with the selenium in your multivitamin, it's easy to go over the 400 mcg limit — add up the labels and adjust
- Note Thyroid medication — How much you need depends on your thyroid condition — talk to your doctor before taking
Combinations
Works well with: Zinc, Iodine, Glutathione
How it appears on the label
| On the label | What it is | What it means |
|---|---|---|
| Selenomethionine L-Selenomethionine | Selenomethionine | Well-absorbed organic selenium |
| Sodium Selenite | Sodium selenite | Inorganic selenium |
Frequently asked questions
How much selenium should I take per day?
The recommended intake is about 60 mcg, and 200 mcg or less from supplements is plenty. Including food and your multivitamin, don't go over 400 mcg a day.
My hair is falling out since I started selenium. Is it related?
Too much selenium can cause hair loss. Add it up with your multivitamin and other products to see if you're over the limit, and stop the selenium for now.
Is selenium good for your thyroid?
Your body needs it to convert thyroid hormone into its active form, and it protects thyroid tissue from oxidative damage. If you have a thyroid condition, talk to your doctor before taking it.
Can I take selenium if I already take a multivitamin?
Many multivitamins already contain selenium. Add up the labels and only add more if your total stays under 400 mcg.
Can selenium keep me up at night?
Yes. Unexplained sleep problems have been reported in people taking selenium-only supplements. If you start sleeping poorly after starting it, try stopping.
If I eat Brazil nuts, do I still need a selenium supplement?
Brazil nuts are very high in selenium, so if you eat them often, you may not need a supplement. In fact, taking both makes it easy to go over the limit.
Related concerns
Last updated 2026-10-12