The guide / Part 25

Vitamin D and memory: what the evidence shows

By The Prolongeva Editorial Team Written from the published research cited in each article Updated October 2026

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Vitamin D shows up in headlines about bones, mood and, now and then, the brain. If you are in your 50s and have noticed memory slips, it is natural to wonder whether a low level is behind it. This guide sticks to what the sources say, and says plainly where they do not agree.

What does vitamin D do, and where does it come from?

The NHS says vitamin D helps regulate the amount of calcium and phosphate in the body, which are needed to keep bones, teeth and muscles healthy. The NHS page does not discuss memory or dementia.

The NHS lists oily fish, red meat, egg yolks, fortified foods and liver as food sources. It also says that from about late March or early April to the end of September, most people in the UK should be able to make all the vitamin D they need from sunlight. That is UK guidance, and what applies to you depends on where you live and how much sun you get.

Who is more likely to be low in vitamin D?

The NHS lists people with limited sun exposure, such as those who are housebound or in care homes, and people who cover their skin outdoors, as groups it advises to take a supplement all year, and says people with dark skin should consider one. For everyone else, it says to consider one in autumn and winter.

On symptoms, the NHS says a lack of vitamin D can lead to rickets in children and to bone pain from osteomalacia in adults. It does not list memory loss.

What do observational studies show?

One large US study, for example, linked low levels to higher dementia risk. In the Cardiovascular Health Study (Littlejohns et al., Neurology, 2014), 1,658 US adults aged 65 or older, free of dementia at the start, had their blood measured in 1992 to 1993 and were followed for a mean of 5.6 years. There were 171 dementia cases.

Compared with people at 50 nmol/L or above, those with severe deficiency (under 25 nmol/L) had a hazard ratio for dementia of 2.25 (95% CI 1.23 to 4.13). Those with deficiency (25 to under 50) had 1.53 (1.06 to 2.21). The authors concluded deficiency is associated with higher risk.

The key word is associated. Observational studies cannot show that low vitamin D caused the dementia. Other differences between people with low and sufficient levels could play a role, and the study alone cannot rule that out. We read the abstract only, so we cannot tell you how the authors handled this.

What happened when people were given supplements?

Randomized trials are the better test of cause. The ones we read looked at older adults and do not show a clear benefit.

• VITAL-Cog. Kang et al. (Scientific Reports, 2021) pooled two ancillary studies of the VITAL trial: 3,424 plus 794 participants aged 60 and older, given 2,000 IU a day of vitamin D3 or placebo for about 2.8 and 2.0 years. The difference in annual decline of a global cognitive score was 0.01 (95% CI -0.01 to 0.02), no significant effect. Among Black participants there was a better result (0.04; 0.01 to 0.08), which the authors say needs confirmation. They note a mostly healthy, well-educated sample, a short follow-up and telephone testing as limits.
• VitaMIND. Corbett et al. (JAMDA, 2025): 620 adults aged 50 or older with mild to moderate vitamin D deficiency and early cognitive impairment, supplement versus placebo for 24 months, done remotely from home. No significant benefit on the primary outcome, an executive function test, or on the other measures.
• Finnish Vitamin D Trial. 2,492 older adults (mean age 68.2), placebo versus 1,600 or 3,200 IU a day of D3 for five years. Dementia diagnoses did not differ significantly (hazard ratios 0.77 and 0.72, both with wide intervals crossing 1). The authors note low power, with only 45 cases, and that participants were largely vitamin D sufficient.

What do we not know?

Quite a lot, and the evidence is mixed.

• Pooled analyses are not unanimous. A meta-analysis of 24 randomized trials with 7,557 participants (mean age 65.2; Chen et al., Neuropsychology Review, 2024) reported a small positive effect on global cognition (Hedges' g 0.128), larger in people with baseline deficiency (0.480), but not in specific cognitive domains. We read only the abstract, and the trials it pooled varied.
• Who might benefit is unclear. The large trials above tested people who were mostly sufficient or only mildly deficient. We found no trial in the sources we read that answers the question for people with severe deficiency.
• Time and doses differ. Two to five years may be too short to see dementia effects, and the studies used different amounts, so results do not line up neatly.
• Memory complaints are not the same as dementia. Most of what we read measured test scores or diagnosed dementia, not everyday forgetfulness in your 50s.

In our reading, the fair summary is: low vitamin D is associated with worse outcomes, and a memory benefit from supplements is not established. For wider context, see normal aging vs. early dementia and nootropic supplements for memory.

Can you take too much?

Yes. The NHS says taking too many vitamin D supplements over a long period can cause too much calcium to build up in the body (hypercalcaemia), which it says can weaken the bones and damage the kidneys and the heart.

The NHS says adults should not take more than 100 micrograms (4,000 IU) of vitamin D a day, because it could be harmful. That is a UK safety ceiling, not a target, and products and doses vary. Check the labels of everything you take, including multivitamins, since vitamin D can come from several at once.

Should you talk to a doctor first?

In our reading, yes, and ideally before buying supplements to treat memory worries. Whether you are low is a question a blood test can answer, and a clinician can judge whether it is worth testing in your case. The NHS page we read does not discuss testing, so that is our suggestion, not the NHS's.

Other reasons to book a visit:

• Memory trouble is new, getting worse, or has been noticed by someone close to you.
• You take medicines or other supplements and are unsure how they combine.
• You have kidney problems or a condition affecting calcium.
• You are in a group the NHS lists as higher risk of deficiency.

Low vitamin D is only one of many things clinicians look at when memory changes. See also vitamin B12 and memory and questions to ask your doctor about memory.

This article is general information, not medical advice. It does not recommend any dose. If you are worried about your memory or your vitamin D level, please talk to a doctor or pharmacist before taking supplements.