Vitamin A
Retinol and beta-carotene, a fat-soluble vitamin and its plant precursor
A fat-soluble vitamin found in liver, eggs and dairy foods, with beta-carotene, which the body can convert to it, in carrots and other orange and green vegetables. People also search for retinol, retinyl palmitate and provitamin A. This page covers only studies in people that gave vitamin A or beta-carotene and measured thinking, memory, mood, stress, sleep, energy, tiredness or quality of life, not all vitamin A research. Within that, it is studied mostly for thinking and memory in children. Here is every one we could find, sorted from each study's summary.
- Found in: liver, eggs, dairy, carrots and leafy greens
- Doses differ between retinol and beta-carotene
- Often given to children for weeks or months
From every paper to the studies that matter
Our search looked only at vitamin A papers on thinking, memory, attention, mood, stress, sleep, energy, tiredness and quality of life, not at all vitamin A research. Many of those measure vitamin A in the blood or the diet rather than giving it. Only a small share gives vitamin A or beta-carotene to people, and that is what this page is about.
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3,816 papers on vitamin A and thinking, mood, sleep or energy.Every record in PubMed, all years
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155 are about people.The rest: 1,255 lab and animal studies, 615 reviews, 1,791 on chemistry, farming and more
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14 give vitamin A or beta-carotene on its own.27 more give it with other vitamins, minerals or ingredients, including cod liver oil
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11 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
- 14 studies giving vitamin A or beta-carotene to people, on thinking, mood, sleep and energy
- 11 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.
- 14,894 people taking part, where studies say
- 75 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
Vitamin A or beta-carotene 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) a day, as each study's summary gives them, and many summaries give no daily dose at all. Retinol, retinyl palmitate and beta-carotene are different forms, so their doses don't compare directly. Beta-carotene doses are its own weight, not converted to retinol, and are usually larger numbers than retinol doses. Some studies gave a large dose once or every few months, mostly to children, and these are averaged per day or shown as the single dose, which is why some dots sit far to the right. Long beta-carotene trials in older adults gave a dose every other day for years.
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 were done in schoolchildren or in people with a long-term condition.
| Study | Who took part | People | Extract and daily dose | Length |
|---|---|---|---|---|
| Poryo 2025RCT, placebo | Extremely low birth weight infants, 2-year follow-up | 759 | Not named | 4 weeks |
| Gutema 2024RCT, placebo | Schoolchildren in southern Ethiopia | 504 | High-dose vitamin A | – |
| Rohani 2022RCT, active or other control | COVID-19 outpatients | 182 | Vitamin A, 7,500 µg | 1 weeks |
| Pitchik 2018RCT, placebo | Children of mothers given prenatal vitamin A or zinc | 198 | Not named | – |
| Ali 2017RCT, placebo | Children aged 8 given vitamin A before birth or at birth | 1,577 | Not named | – |
| Bitarafan 2016RCT, placebo | Relapsing-remitting multiple sclerosis patients | 101 | Retinyl palmitate, 7,500 µg | 52 weeks |
| Buckley 2013RCT, placebo | Children of mothers supplemented before and after pregnancy | 390 | Retinol (vitamin A), 1,000 µg | 182 weeks |
| Lima 2013RCT, placebo | Shantytown children at risk of diarrhea | 167 | Retinol (vitamin A) | – |
| Mitter 2012RCT, active or other control | Shantytown children with low height-for-age | 213 | Retinol (vitamin A), 490 µg | 52 weeks |
| Kang 2009RCT, placebo | Women with or at risk of cardiovascular disease | 2,824 | Beta-carotene, 25,000 µg | 281 weeks |
| Ma 2008RCT, active or other control | Anemic pregnant women | 366 | Retinol (vitamin A), 2,000 µg | 9 weeks |
| Grodstein 2007RCT, placebo | Older male physicians | 5,956 | Beta-carotene, 25,000 µg | 936 weeks |
| Smith Fawzi 2007RCT, placebo | HIV-positive pregnant women | 1,078 | Retinol (vitamin A) | – |
| Jinabhai 2001RCT, placebo | Rural schoolchildren aged 8-10 | 579 | Not named | 16 weeks |
What's known about safety
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In trials
Too much vitamin A over many years may affect the bones and make fractures more likely in older age. We found no review of side effects in the studies listed here, and many studies don't report them. Some trials of beta-carotene ran for years, at 6 to 50 mg a day in the studies a 2023 review covered.
NHS vitamins and minerals, Vitamin A; Abrego-Guandique 2023, review of 16 studies of beta-carotene and cognition, Oct 2026
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In the UK
Retinol, retinyl acetate, retinyl palmitate and beta-carotene are permitted forms of vitamin A in food supplements. The NHS says a daily intake from food and supplements of 1.5 mg (1,500 µg) or less is unlikely to cause harm, and gives adult needs as 700 µg for men and 600 µg for women.
Directive 2002/46/EC Annex II as retained in UK law (legislation.gov.uk); NHS vitamins and minerals, Vitamin A, Oct 2026
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Check first
The NHS says anyone who is pregnant should avoid liver and liver products, and that people who eat liver every week should not take supplements containing vitamin A. It also says beta-carotene supplements have been found to raise the risk of lung cancer in people who smoke, and that people who smoke or have been exposed to asbestos are advised not to take them. Speak to a pharmacist or doctor first if this applies to you or you take regular medicines. We found no source on medicine interactions.
NHS vitamins and minerals, Vitamin A and Others pages, Oct 2026
Where these studies come from
We list every published study in people that gave vitamin A and measured thinking, memory, attention, mood, stress, sleep, energy, tiredness or quality of life, so this is not all vitamin A research. Retinol, retinyl palmitate or acetate and beta-carotene given as a supplement count. Studies that only measured vitamin A in the blood or the diet are left out, as are retinoid drugs such as isotretinoin and tretinoin. Reports of the same trial count once. Vitamin A on its own means it was the only difference between the groups, including when it was added to usual care or a medicine. Vitamin A given with other vitamins, minerals or ingredients, including cod liver oil, 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, 14 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 vitamin A 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.
