Vitamin D and Memory: What a New Study Really Found
Introduction
Vitamin D is best known for helping maintain healthy bones and muscles. In recent years, researchers have also been asking whether it may play a role in brain health, particularly as people age.
A new study from Emory University has brought that question back into the spotlight. Researchers reported that older adults with mild cognitive impairment and sleep disturbance who said they were taking at least 5,000 international units (IU) of vitamin D each day had higher scores on a cognitive screening test than people who reported taking none. [1]
The headline sounds striking. But the study was small, it did not give vitamin D to participants as part of an experiment, and it measured supplement use and cognition at the same point in time. That means it found an association - not proof that taking 5,000 IU improves thinking.
What is mild cognitive impairment?
Mild cognitive impairment, often called MCI, describes noticeable changes in memory or thinking that are greater than expected with normal ageing but are not severe enough to stop a person from carrying out most everyday activities independently.
Some people with MCI remain stable or even improve, while others go on to develop dementia. Because MCI can have many causes, concerns about memory or thinking should be assessed by a healthcare professional rather than treated with supplements alone.
Why might vitamin D be linked to brain health?
Vitamin D receptors are found in many tissues, including the brain. Researchers have proposed several ways vitamin D could be connected with cognition, including effects on inflammation, nerve-cell function and blood-vessel health. Low vitamin D levels have also been associated with poorer cognitive outcomes in observational studies.
However, an association does not automatically mean that low vitamin D causes cognitive decline. People who are frail, spend less time outdoors, exercise less, have poorer diets or have other illnesses may also have lower vitamin D levels. Randomized clinical trials are therefore important because they can test whether giving vitamin D actually changes cognitive outcomes.
What did the new 2026 study do?
The study, published in Sleep Medicine, included 54 adults with diagnosed or suspected MCI who also had sleep disturbance. Their average age was about 67 years. Participants completed the Montreal Cognitive Assessment, or MoCA, a 30-point screening test that looks at areas such as memory, attention, language and executive function. [1]
Vitamin D use was self-reported. Participants were grouped according to how much vitamin D they said they took each day: none, less than 1,000 IU, 1,000-1,999 IU, 2,000-4,999 IU, or 5,000 IU and above. Only 12 participants were in the highest-dose group. [1]
After adjusting for factors including age, sex, body mass index and education, the researchers found that people reporting at least 5,000 IU per day had MoCA scores about 3.78 points higher than those reporting no daily vitamin D. Lower dose groups were not significantly different from the no-supplement group. [1]
So where did the "13% higher" figure come from?
The MoCA is scored out of 30. A difference of 3.78 points is about 12.6% of the test's maximum possible score, which is why the finding has been described in news coverage as roughly 13% higher.
That wording can be misleading if it sounds like people improved by 13% after starting vitamin D. They did not. The researchers did not measure cognition before and after treatment. They compared different people at one point in time. The study therefore cannot tell us whether vitamin D caused the score difference.
The study at a glance
Question | What the study found | What it means |
Who was studied? | 54 adults with MCI or suspected MCI plus sleep disturbance; average age 67. | A small and very specific group, so the result may not apply to all older adults. |
Who took 5,000+ IU? | 12 participants reported taking at least 5,000 IU daily. | The key finding is based on a very small high-dose subgroup. |
What was the cognitive result? | The 5,000+ IU group had an adjusted MoCA score 3.78 points higher than the no-vitamin-D group. | This is an association, not a before-and-after improvement. |
Did lower doses help? | No statistically significant association was found for lower dose categories. | The study does not establish a clear dose-response effect. |
Was this a treatment trial? | No. It was a cross-sectional observational study using self-reported supplement intake. | It cannot prove that vitamin D caused better cognition. |
Why the result is interesting
The study focused on people who had both MCI and sleep problems, a combination that may place extra stress on cognition. Nearly all participants met criteria for poor sleep, and sleep disturbance itself has been linked with worse cognitive health.
The finding also raises a reasonable scientific question: could vitamin D status matter more in certain high-risk groups than in the general population? That is worth studying. But an observational result is best viewed as a reason to run a proper randomized trial, not as a reason to start high-dose supplements.
What does the wider research show?
The broader evidence is mixed. Some randomized studies have reported improvements, while several larger trials have found no meaningful cognitive benefit.
In a 2020 randomized trial of 183 older adults with MCI, 800 IU of vitamin D per day for 12 months was associated with improvements in several cognitive measures compared with placebo. [2]
By contrast, two cognitive substudies of the large VITAL trial tested 2,000 IU of vitamin D3 per day in adults aged 60 and older and found no overall reduction in cognitive decline over roughly two to three years. [3]
More recently, the 2025 VitaMIND randomized trial enrolled 620 adults aged 50 and older with mild-to-moderate vitamin D deficiency and early cognitive impairment. Daily vitamin D supplementation for 24 months did not improve executive function, overall cognition, daily function or well-being compared with placebo. [4]
A 2026 systematic review and meta-analysis of randomized trials found a modest average improvement in global cognition and some cognitive domains with vitamin D, but the included trials differed considerably in their populations, doses, tests and methods. The authors concluded that more high-quality trials are needed. [5]
How the major studies compare
Study | Main finding | How to interpret it |
Zhou et al., 2026 [1] | 5,000+ IU/day was associated with a 3.78-point higher MoCA score in 54 adults with MCI and sleep problems. | Interesting but observational; only 12 people were in the high-dose group. |
Yang et al., 2020 [2] | 800 IU/day improved several cognitive measures over 12 months in 183 adults with MCI. | Randomized trial, but relatively small and needs replication. |
VITAL cognitive studies, 2021 [3] | 2,000 IU/day did not improve overall cognitive decline in large older-adult substudies. | Stronger evidence against a large benefit in generally healthy older adults. |
VitaMIND, 2025 [4] | Daily vitamin D did not improve cognition over 24 months in 620 adults with deficiency and early cognitive impairment. | A larger randomized trial with a negative result. |
Meta-analysis, 2026 [5] | Pooled trials suggested modest gains in some areas of cognition. | Overall evidence remains inconsistent because studies differ substantially. |
What the new study does NOT prove
It does not prove that 5,000 IU of vitamin D improves memory.
It does not show that vitamin D prevents Alzheimer disease or other dementias.
It does not show that people should increase their dose to 5,000 IU per day.
It does not establish that more vitamin D is better. Lower dose groups did not show the same association.
It does not rule out other explanations for the score difference, such as health behaviours, diet, medical care or other unmeasured factors.
Is 5,000 IU of vitamin D a high dose?
Yes. The authors of the 2026 study note that 5,000 IU per day is above the commonly used tolerable upper intake level of 4,000 IU per day for adults. [1]
High-dose vitamin D is sometimes prescribed for specific medical reasons, but more is not automatically better. In a three-year randomized trial of healthy adults aged 55 to 70, daily doses of 4,000 IU and 10,000 IU did not improve bone health and were associated with greater loss of volumetric bone density than 400 IU per day. [7]
Excessive vitamin D can also raise calcium levels in the blood or urine. The risk depends on the dose, duration, other supplements and a person's medical conditions. People with kidney disease, a history of kidney stones, disorders affecting calcium metabolism or certain medications may require particular caution.
Should you take vitamin D for memory?
At present, there is not enough evidence to recommend high-dose vitamin D as a treatment for MCI or as a way to prevent dementia.
If you are vitamin D deficient, treating that deficiency is important for established reasons such as bone and muscle health. But correcting a deficiency is different from taking a high dose specifically to improve cognition.
If you are worried about memory, concentration or thinking, speak with a healthcare professional. Cognitive symptoms can have many contributors - including sleep problems, medications, depression, thyroid disease, vitamin B12 deficiency, hearing loss and other medical conditions - and some of these may be treatable.
What can people do for brain health now?
No single supplement has been shown to protect the brain on its own. Brain health is influenced by many factors, and the strongest approach is usually to address several of them together.
Stay physically active within your abilities.
Treat high blood pressure, diabetes and other cardiovascular risk factors.
Prioritize good-quality sleep and seek help for persistent sleep problems.
Maintain social and mentally stimulating activities.
Eat a balanced diet and correct proven nutritional deficiencies with appropriate medical guidance.
Have new or worsening cognitive symptoms assessed rather than assuming they are part of normal ageing.
The takeaway
The new study provides an intriguing clue, not a treatment recommendation. Among 54 people with both MCI and sleep disturbance, the 12 participants who reported taking at least 5,000 IU of vitamin D each day scored about 3.78 points higher on the MoCA than people taking none. [1]
Because the study was small and observational, it cannot show that high-dose vitamin D caused better cognition. Larger randomized trials have produced mixed results, including several that found no benefit. For now, high-dose vitamin D should not be viewed as a proven memory treatment or dementia-prevention strategy.
Sources
1. Zhou S, Sudeshna P, Trotti LM, Bliwise D, Pak V. Vitamin D supplement intake is associated with better cognition in persons with sleep disturbance and mild cognitive impairment. Sleep Medicine. 2026;146:108960. doi:10.1016/j.sleep.2026.108960. PMID: 42287971.
2. Yang T, Wang H, Xiong Y, et al. Vitamin D Supplementation Improves Cognitive Function Through Reducing Oxidative Stress Regulated by Telomere Length in Older Adults with Mild Cognitive Impairment: A 12-Month Randomized Controlled Trial. Journal of Alzheimer's Disease. 2020;78(4):1509-1518. doi:10.3233/JAD-200926. PMID: 33164936.
3. Kang JH, Vyas CM, Okereke OI, et al. Effect of vitamin D on cognitive decline: results from two ancillary studies of the VITAL randomized trial. Scientific Reports. 2021;11(1):23253. doi:10.1038/s41598-021-02485-8. PMID: 34853363.
4. Corbett A, Taylor R, Llewellyn D, et al. Impact of Vitamin D Supplementation on Cognition in Adults With Mild to Moderate Vitamin D Deficiency: Outcomes From the VitaMIND Randomized Controlled Trial. Journal of the American Medical Directors Association. 2025;26(8):105711. doi:10.1016/j.jamda.2025.105711. PMID: 40480279.
5. Behrouzi R, Shahinfar H, Jazayeri S. Effects of Vitamin D Supplementation on Cognitive Function in Older Adults: A GRADE Methodology-Assessed Systematic Review and Meta-Analysis of Randomized Clinical Trials. Nutrition Reviews. 2026;nuaf284. doi:10.1093/nutrit/nuaf284. PMID: 42100929.
6. Rossom RC, Espeland MA, Manson JE, et al. Calcium and vitamin D supplementation and cognitive impairment in the Women's Health Initiative. Journal of the American Geriatrics Society. 2012;60(12):2197-2205. doi:10.1111/jgs.12032. PMID: 23176129.
7. Burt LA, Billington EO, Rose MS, Raymond DA, Hanley DA, Boyd SK. Effect of High-Dose Vitamin D Supplementation on Volumetric Bone Density and Bone Strength: A Randomized Clinical Trial. JAMA. 2019;322(8):736-745. doi:10.1001/jama.2019.11889. PMID: 31454046.
Image: OmegaQuant. “Can Vitamin D Deficiency Cause Memory Loss?” Judy Blatman, 28 Dec. 2021. Retrieved 28 Aug. 2026.
Assessed and Endorsed by the MedReport Medical Review Board
