A 200 mcg selenium pill is half of the US adult upper limit of 400 mcg a day. But food already gives the average American adult 94 to 132 mcg a day. Add the pill, and an average adult lands near 300 mcg. That is above Europe's newer limit of 255 mcg. One long trial at exactly 200 mcg found more type 2 diabetes, and another found more hair loss.
This article provides general information about medication and supplement use and is not a substitute for professional medical advice. Always consult your doctor or pharmacist before making changes to your medication or supplement routine.
Is 200 mcg of Selenium Daily Too Much?
The NIH Office of Dietary Supplements lists the adult Recommended Dietary Allowance at 55 mcg and the Tolerable Upper Intake Level at 400 mcg. The upper limit is the highest daily intake that is unlikely to cause harm in most people.
So a 200 mcg pill is almost four times the daily recommended amount, but half of the ceiling. The catch: the ceiling counts all selenium, from food and pills together. Your body can absorb up to about 90% of the selenium in common supplement forms.
How Much Selenium Per Day Is Too Much? Why the Limits Disagree
You will find three different "maximums" when you search:
| Source | Adult daily limit | What it covers |
|---|---|---|
| US (NIH, Food and Nutrition Board) | 400 mcg | Food plus supplements, including pregnancy |
| Europe (EFSA, 2023) | 255 mcg | Food plus supplements, including pregnancy and breastfeeding |
| Some health websites | 200 mcg | Supplements taken long term |
The European number is the newest. In its 2023 opinion, the European Food Safety Authority used hair loss as an early sign of too much selenium. It found a "lowest-observed-adverse-effect-level" of 330 mcg a day in the SELECT trial. Then it applied an uncertainty factor of 1.3 to get 255 mcg.
This is where 200 mcg comes back in. SELECT gave men 200 mcg a day, and EFSA estimated they already got about 130 mcg from their diet. So 330 mcg was the pill plus a normal diet. The selenium group had more hair loss than placebo (relative risk 1.28). Europe's lower limit was built from people taking 200 mcg on top of their usual meals.
How Much Selenium Per Day for a Woman or a Man, Counting Food
Most people in the US are not low in selenium. National survey data in the NIH fact sheet show adult women get about 94 mcg a day from food and drinks on average, and adult men get about 132 mcg.
Here is our math when you add a 200 mcg pill:
| Who | Average from food | Food + 200 mcg pill | Under US limit (400)? | Under Europe's limit (255)? |
|---|---|---|---|---|
| Adult woman | 94 mcg | about 294 mcg | Yes | No |
| Adult man | 132 mcg | about 332 mcg | Yes | No |
| Adult man + 1 Brazil nut a day | 132 + 68 to 91 mcg | about 400 to 423 mcg | At or over | No |
The average man taking 200 mcg lands near the 330 mcg total where SELECT saw more hair loss. Your own diet could be well above or below these averages.
Also check your multivitamin. Many multis already contain 55 mcg, so a multi plus a 200 mcg pill is 255 mcg before you eat anything.
Selenium Supplements and Diabetes Risk: What the 200 mcg Trials Found
200 mcg is not a random number. It is the dose that the largest selenium trials actually tested, for years at a time.
| Trial | Who took part | Daily dose | What happened |
|---|---|---|---|
| NPC trial (Stranges, 2007) | 1,202 US adults with past skin cancer, no diabetes at the start | 200 mcg selenium yeast | Over about 7.7 years, 58 people on selenium got type 2 diabetes vs 39 on placebo |
| SELECT (Lippman, 2009) | 35,533 men age 50 and up | 200 mcg selenomethionine | No drop in prostate cancer. Diabetes was slightly higher, but not statistically significant |
| Denmark PRECISE (Rayman, 2018) | 491 adults age 60 to 74 | 100, 200, or 300 mcg | Only the 300 mcg group had higher death rates over the full follow-up. 100 and 200 mcg showed no significant change |
| Graves' eye disease (Marcocci, 2011) | 159 people with mild Graves' orbitopathy (three groups) | 100 mcg twice a day, for 6 months | Better quality of life and slower eye disease than placebo. No side effects were seen with selenium |
The diabetes signal is the one to know about. In the NPC trial, the risk was about 55% higher in the selenium group (hazard ratio 1.55). It was highest in people who started with the most selenium in their blood. Diabetes was a secondary result, and the authors wrote that selenium "may increase risk for the disease." They did not say it causes it.
When EFSA pooled five trials, the risk was about 11% higher, a borderline result that came mostly from SELECT. The panel said the evidence "suggests a positive relationship" between selenium intake and diabetes.
Researchers looking at SELECT also found more high-grade prostate cancer in men who started with high selenium. According to the NIH fact sheet, those researchers recommended that men over 55 avoid selenium supplements at doses above recommended intakes. If you have diabetes, prediabetes, or prostate concerns, ask your doctor before taking selenium long term.
200 mcg Selenium and Brazil Nuts: How Many Nuts Is That?
Brazil nuts are the richest food source of selenium by far. The NIH fact sheet lists 1 ounce (6 to 8 nuts) at about 544 mcg, and 68 to 91 mcg per nut. By our math, two or three nuts can roughly equal a 200 mcg pill.
The real number swings a lot. EFSA notes that 5 or 6 Brazil nuts could give about 100 to 2,000 mcg, depending on where they grew. It named regular Brazil nut eaters and people on high-dose supplements as the exceptions who could go over its limit.
Is 200 mcg of Selenium Safe During Pregnancy?
It depends on which group you ask, so settle this one with your OB or endocrinologist.
- The US limit in pregnancy is still 400 mcg, and the RDA rises a little to 60 mcg (NIH).
- Europe's limit of 255 mcg applies to pregnant and breastfeeding women too. A 200 mcg pill plus food can pass it.
- One trial gave 200 mcg of selenomethionine to pregnant women with thyroid antibodies (TPO antibodies). Fewer of them had thyroid problems after birth: 28.6% vs 48.6% on placebo (Negro, 2007).
- Other trials were mixed. In 2017, the American Thyroid Association made a weak recommendation against selenium supplements for pregnant women with TPO antibodies, based on moderate-quality evidence (NIH summary).
Also check your prenatal vitamin label for selenium before adding a separate pill.
Selenium for Hashimoto's and Thyroid Eye Disease: Why Some Doctors Use 200 mcg
Sometimes 200 mcg is a doctor's plan, not a guess. The NIH notes that the upper limits "do not apply to people who are taking selenium under the care of a physician."
For mild Graves' eye disease, a 6-month course of 100 mcg twice a day helped in the Marcocci trial. European guidelines from 2021 list selenium for mild, active cases in "selenium-deficient areas."
For Hashimoto's, the evidence is split. In a review of 16 trials using 80 to 200 mcg a day, selenium lowered TPO antibodies in people already taking levothyroxine. But a review of 9 trials of selenium alone found no change in TSH, thyroid ultrasound, or quality of life. Those authors said the evidence does not support using it (NIH summary). If you have a thyroid condition, ask your endocrinologist whether selenium belongs in your plan, and at what amount.
If you take levothyroxine, see vitamins that interfere with thyroid medication and the best time to take levothyroxine.
Signs of Too Much Selenium
The NIH lists these signs of too much selenium over time:
- Garlic smell on your breath and a metallic taste (early signs)
- Hair loss
- Brittle nails or nail loss
- Skin rash, nausea, diarrhea
- Tiredness, irritability, nerve problems
Very large overdoses are rare but serious. In 2008, a liquid supplement was labeled as having "200 μg of selenium per fluid ounce." Testing found "approximately 200 times the labeled concentration" (MacFarquhar, 2010). Of 201 people sickened, about 7 in 10 had hair loss. Among those followed up 90 days or more later, 29% (16 of 56) still had hair loss. That was an employee error at an ingredient supplier, not a normal 200 mcg pill. If you suspect someone took a large amount, call Poison Control at 1-800-222-1222 right away.
Hair Loss or Nail Changes on Selenium: Is It the Selenium or Something Else?
If your hair is thinning, selenium is only one suspect. If you take selenium for a thyroid problem, the thyroid itself may be the cause. An underactive thyroid can cause dry, thinning hair. Low iron and other nutrients can play a part too, as we explain in which vitamin deficiency causes hair loss.
Selenium may also be in more than one bottle, like a multivitamin plus a selenium pill. Selenium-only pills usually hold 100 to 400 mcg. Bring every bottle to your pharmacist to add up the total, and ask your doctor about checking your thyroid and iron.
How Pillo Helps You Keep Track
Selenium hides in several products. In Pillo, you can put every supplement in your medication list, add a dose note with the mcg on each label, and show the full list to your pharmacist. If you also take levothyroxine, Pillo's persistent alarm keeps ringing until you deal with it, so the thyroid pill does not slide.
Pillo is free for unlimited medications, with ads. Download Pillo on Google Play
Other supplement limits: magnesium, iron, vitamin D, and melatonin.
Consult your doctor or pharmacist for advice specific to your medications.
FAQ
Is 200 mcg of selenium safe to take every day?
It is under the US adult limit of 400 mcg. Once you add an average diet, it is above Europe's limit of 255 mcg. One long trial at 200 mcg a day found more type 2 diabetes than placebo, and another found more hair loss. Ask your doctor whether you need it and for how long.
How many Brazil nuts equal 200 mcg of selenium?
About two or three nuts, using the NIH figure of 68 to 91 mcg per nut. But the amount varies widely by where the nuts grew, so this is only a rough guide.
What are the first signs of too much selenium?
The NIH lists a garlic smell on the breath and a metallic taste in the mouth as early signs. Hair loss and brittle nails are the most common signs of long-term excess.
Is 200 mcg of selenium safe during pregnancy?
Groups disagree. The US limit in pregnancy is 400 mcg, while Europe's 255 mcg limit includes pregnancy. According to the NIH, the American Thyroid Association made a weak recommendation against selenium supplements for pregnant women with TPO antibodies. Talk with your OB before taking it.
Can I take selenium with levothyroxine?
Some people with Hashimoto's take both. Trials summarized by the NIH found selenium lowered thyroid antibodies in people on levothyroxine, while a separate review of selenium alone found no change in TSH or quality of life. Ask your doctor or pharmacist how it fits your thyroid plan.
