Selenium
Se, a trace mineral
A trace mineral the body needs in small amounts, found in Brazil nuts, fish, meat and eggs. This page covers only studies in people that gave selenium and measured thinking, memory, mood, stress, sleep, energy, tiredness or quality of life, not all selenium research. Within that, it is studied mostly for mood and for memory and thinking, often in people with depression, a thyroid condition or dementia. Here is every one we could find, sorted from each study's summary.
- Found in: Brazil nuts, fish, meat and eggs
- Most tested: 200 µg a day
- Mostly taken daily for weeks or months
From every paper to the studies that matter
Our search looked only at selenium papers on thinking, memory, mood, stress, sleep, energy and quality of life, not at all selenium research. Most of those measure selenium in the blood or the diet rather than giving it. Only a small share gives selenium to people, and that is what this page is about.
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3,567 papers on selenium and thinking, mood, sleep or energy.Every record in PubMed, all years
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111 are about people.The rest: 1,295 lab and animal studies, 662 reviews, 1,499 on chemistry, farming and more
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32 give selenium on its own.37 more give selenium with vitamins, other minerals or other ingredients
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19 are randomised against a placebo.Randomised controlled trials In a randomised controlled trial, people are put into groups by chance, one taking the treatment and one a placebo or other comparison. Chance spreads differences such as age and health evenly, so a difference between the groups is more likely to be down to the treatment., the strongest kind of study
Bar lengths use a square-root scale so the small numbers stay visible.
How much research there is
- 32 studies giving selenium to people, on thinking, mood, sleep and energy
- 19 of them randomised against a placebo A placebo-controlled trial compares a real treatment with a dummy that looks the same, the placebo. People often feel better when they expect to, so comparing against a placebo shows how much of the change comes from the treatment itself.
- 16,929 people taking part, where studies say
- 80 systematic reviews A systematic review searches for every study on a question in a set, written-down way, judges the quality of each and sums up what they show together. Many include a meta-analysis. The Atlas lists these as pooled reviews. pooling the trials
Studies in people, by year published
Selenium on its own.
What the studies looked at
Each study can measure several things. Choose a topic to see its studies in the list below.
Studies in people with a diagnosed condition are counted here and listed with their population. We describe what they measured, not what they might treat. Most studies also report safety; see below.
What was tested, and how much
Doses are in micrograms (µg) of selenium a day, as each study's summary gives them. Studies used different forms, such as sodium selenite, selenomethionine, selenium yeast and Brazil nuts, and many summaries don't name the form. For Brazil nuts the dose is the selenium the nuts were said to contain. A few trials in Alzheimer's disease and a related dementia gave sodium selenate as a drug at about 30,000 µg (30 mg) a day, far above the other studies, and they are shown with that dose. Most studies gave selenium by mouth every day for weeks or months.
Daily amount, one dot per study
Studies per extract
Named extracts are the maker's brand. "Not named" means the study didn't say.
All studies in people
Filter the list, then open a study on PubMed. Each row comes from the study's published summary, and many follow people with a long-term condition.
| Study | Who took part | People | Extract and daily dose | Length |
|---|---|---|---|---|
| Huang 2026RCT, active or other control | Graves' hyperthyroidism with low MoCA | 124 | Not named | 12 weeks |
| Noormohammadi 2026RCT, placebo | Adults with major depression on sertraline | 50 | Nano-selenium, 55 µg | 12 weeks |
| Bahari 2026RCT, placebo | Type 2 diabetes with neuropathy | 50 | Selenium-enriched yeast, 200 µg | 8 weeks |
| Silva 2025Non-randomised controlled | Women on energy-restricted diet | 56 | Brazil nut, 347 µg | 8 weeks |
| Noormohammadi 2025RCT, placebo | Adults with major depression on sertraline | 50 | Nano-selenium, 55 µg | 12 weeks |
| Rahimi 2024RCT, placebo | Postpartum women | 108 | Selenium yeast and sodium selenite, 200 µg | 8 weeks |
| Balali 2024RCT, placebo | Patients with migraine | 72 | Not named, 200 µg | 12 weeks |
| Silveira 2024Non-randomised controlled | Women with overweight or obesity on diet | 56 | Brazil nuts, 347 µg | 8 weeks |
| Noormohammadi 2024RCT, placebo | Adults with major depression on sertraline | 50 | Nano-selenium, 55 µg | 12 weeks |
| Pfister 2023Observational | Cancer rehabilitation patients | 271 | Sodium selenite, 600 µg | – |
| Mesdaghinia 2023RCT, placebo | High-risk pregnant women | 60 | Selenium amino acid chelate, 200 µg | 12 weeks |
| Krysiak 2023Non-randomised controlled | Women with euthyroid Hashimoto's thyroiditis | – | Selenomethionine | – |
| Vivash 2022Single-arm or open-label | Behavioural variant frontotemporal dementia | 12 | Sodium selenate, 45,000 µg | 52 weeks |
| Dilcher 2022Single-arm or open-label | Behavioural variant frontotemporal dementia | 11 | Sodium selenate | 52 weeks |
| Vivash 2021Single-arm or open-label | Alzheimer's disease patients | 28 | Sodium selenate, 30,000 µg | 100 weeks |
| Cavedon 2020RCT, placebo | Adults with obesity on low-calorie diet | 37 | L-selenomethionine, 240 µg | 12 weeks |
| Tamtaji 2019RCT, placebo | Alzheimer's disease patients | 79 | Not named, 200 µg | 12 weeks |
| Cardoso 2019RCT, placebo | Alzheimer's disease patients | 40 | Sodium selenate, 30,000 µg | 24 weeks |
| Li 2018Single-arm or open-label | Schizophrenia patients | – | Selenium Weikang | 13 weeks |
| Kryscio 2017RCT, placebo | Older men without dementia | 7,540 | Not named, 200 µg | – |
| Malpas 2016RCT, placebo | Mild-moderate Alzheimer's disease patients | 40 | VEL015 (sodium selenate), 30,000 µg | 24 weeks |
| Rita Cardoso 2016RCT, active or other control | Older adults with mild cognitive impairment | 31 | Brazil nuts, 290 µg | 26 weeks |
| Calissendorff 2015RCT, placebo | Graves' thyrotoxicosis patients | 38 | Not named, 200 µg | 36 weeks |
| Vieira 2015Crossover, placebo | Children with cancer on chemotherapy | – | Selenium supplement | 52 weeks |
| Voĭtsekhovskis 2014Non-randomised controlled | PTSD risk group during military mission | – | Organic selenium | – |
| Kryscio 2013RCT, placebo | Older men in PREADViSE prevention trial | 7,547 | Not named, 200 µg | – |
| Derbeneva 2012Non-randomised controlled | Cardiovascular disease with obesity | 59 | Selenium-enriched diet product | 3 weeks |
| Mokhber 2011RCT, placebo | Pregnant women, postpartum depression follow-up | 166 | Not named, 100 µg | – |
| Rayman 2006RCT, placebo | Older UK adults aged 60-74 | 501 | High-selenium yeast | 26 weeks |
| Shor-Posner 2003RCT, placebo | HIV-positive drug users | 63 | Not named, 200 µg | 52 weeks |
| Hawkes 1996Non-randomised controlled | Healthy men in metabolic unit | 11 | Not named, 356 µg | 14 weeks |
| Benton 1991Crossover, placebo | Healthy British adults | 50 | Not named, 100 µg | 5 weeks |
What's known about safety
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In trials
Too much selenium can cause hair loss and brittle nails, and EFSA saw hair loss in a large trial at 330 µg a day. In Alzheimer's trials of sodium selenate at about 30 mg a day, side effects were no more common than on placebo over 24 weeks, but nail changes and hair loss were common over longer use. A supplement made in error with about 200 times the labelled selenium caused hair loss, nail changes and stomach upset.
EFSA 2023 opinion on selenium; Malpas 2016, 40 people over 24 weeks; Vivash 2021, 28 people for up to 23 months; Aldosary 2012, case series
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In the UK
Selenium is a permitted mineral in food supplements, as sodium selenite or selenate, L-selenomethionine or selenium yeast. The NHS says 350 µg a day or less from supplements is unlikely to cause harm. EFSA set a lower upper limit in 2023, 255 µg a day in all for adults, including in pregnancy and breastfeeding.
Directive 2002/46/EC Annex II as retained in UK law (legislation.gov.uk); NHS vitamins and minerals, Others; EFSA 2023 opinion on selenium, Oct 2026
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Check first
Selenium from supplements, multivitamins and Brazil nuts adds up, and EFSA says regular users of high-dose supplements or Brazil nuts may go over the upper limit. A review of pooled studies linked higher selenium intake with a possibly higher risk of type 2 diabetes. We found no UK guidance on how it mixes with medicines. Speak to a pharmacist or doctor first if you have diabetes or take regular medicines.
EFSA 2023 opinion on selenium; Wang 2023, umbrella review of meta-analyses; searches of NHS and FSA, Oct 2026
Where these studies come from
We list every published study in people that gave selenium and measured thinking, memory, mood, stress, sleep, energy, tiredness or quality of life, so this is not all selenium research. Sodium selenite and selenate, selenomethionine, selenium yeast and Brazil nuts all count. Studies that only measured selenium in the blood, hair or diet are left out, and reports of the same trial count once. Selenium on its own means it was the only difference between the groups, including when it was added to a medicine or usual care. Selenium given with vitamins, other minerals or plant extracts counts as a blend. This first version is built from each study's summary; full-paper checks come next.
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We search
PubMed, the world's main library of medical research, for every paper on L-theanine.
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We keep studies in people
Lab and animal work is counted but left out of the list, because it doesn't tell you what happens in people.
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We note the basics
Who took part, how many, how much and for how long, from each study's published summary. A second check corrects what the first read gets wrong.
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We read them in full
Results appear once we've read the whole paper and checked every number. The date at the top shows when this entry was last updated.
Download the study list
Every study in people as a spreadsheet, 32 rows, free to reuse with a link back.
Versions
Each update to the data gets a new version number, so you can tell what changed and when.
See every version
1.0 · 24 Oct 2026. First release. Every published study giving selenium to people that measured thinking, memory, mood, stress, sleep, energy or quality of life is listed from its summary. None is read in full yet.
