Dementia affects roughly 55 million people worldwide, with nearly 10 million new cases diagnosed each year [1]. By 2050, that number is projected to reach 139 million. If you’ve watched a family member struggle with memory loss, you’ll understand why people are desperate for anything that might help.

I’ve gone through the clinical research on three supplements commonly promoted for dementia: ginkgo biloba, vitamin D, and omega-3 fatty acids. The results are more complicated than supplement marketing would suggest, and in some cases, quite disappointing.

Understanding dementia

Dementia isn’t a single disease. It’s an umbrella term for a collection of symptoms affecting memory, thinking, and social abilities severely enough to interfere with daily life. Alzheimer’s disease accounts for 60-70% of cases, followed by vascular dementia, Lewy body dementia, and frontotemporal dementia [2].

Several modifiable risk factors have been identified: physical inactivity, smoking, excessive alcohol consumption, air pollution, head injuries, limited social contact, poorly controlled diabetes, high blood pressure, obesity, depression, and hearing loss. The Lancet Commission estimates that addressing these factors could prevent or delay up to 40% of dementia cases [3].

That’s the context in which supplement research happens. People are understandably looking for something they can take to reduce their risk or slow progression.

1. Ginkgo biloba

Ginkgo biloba is the supplement people ask about most often. The standardised extract (EGb 761) contains flavonoid glycosides and terpenes that are thought to have antioxidant properties and may improve cerebral blood flow.

What the evidence shows

For people who already have dementia, there’s some evidence that ginkgo may help with behavioural symptoms. A meta-analysis of nine trials found that EGb 761 at 240mg daily for 22-24 weeks improved scores on the Neuropsychiatric Inventory compared to placebo [4]. The improvements were seen in depression, irritability, anxiety, aggression, apathy, and sleep disturbances. However, symptoms like delusions and hallucinations didn’t change significantly.

That’s a reasonable finding, but it needs context. The improvements were statistically significant but clinically modest. And these studies looked at symptom management, not disease modification.

Can ginkgo prevent dementia?

This is where things get disappointing. The GuidAge study followed 2,854 people aged 70 and older who had memory complaints but didn’t have dementia [5]. Half took EGb 761 (240mg daily) and half took placebo. After five years, there was no significant difference in dementia rates between the groups.

The Ginkgo Evaluation of Memory (GEM) study in the United States reached a similar conclusion. More than 3,000 participants aged 75 and older took either ginkgo or placebo for a median of 6.1 years. Ginkgo did not reduce the incidence of dementia or Alzheimer’s disease [6].

My honest assessment: ginkgo might help manage some behavioural symptoms in people who already have dementia, but there’s no good evidence it prevents the condition from developing. If someone is taking it hoping to avoid dementia, they should know the prevention data is negative.

Safety considerations

Ginkgo is generally well tolerated, but it has blood-thinning effects. Anyone taking aspirin, warfarin, or other anticoagulants should discuss ginkgo with their doctor before using it. There have been rare reports of bleeding complications [7].

2. Vitamin D

Vitamin D receptors are found throughout the brain. The vitamin is involved in neurotransmitter synthesis and nerve growth factor production, and it may protect against oxidative stress. Researchers have therefore investigated whether vitamin D deficiency contributes to dementia risk.

The observational evidence

Multiple studies have found that people with low vitamin D levels have a higher risk of developing dementia. A meta-analysis of 37 studies found that vitamin D deficiency was associated with a 33% increased risk of dementia [8]. Another large study using UK Biobank data found that very low vitamin D levels (below 25 nmol/L) were associated with a 54% higher dementia risk compared to adequate levels [9].

That sounds alarming, but observational studies can’t prove causation. People with low vitamin D might also be less physically active, spend less time outdoors, have poorer overall nutrition, or have underlying health conditions. Any of these factors could explain the association.

Does supplementation help?

Here’s where the research gets frustrating. Despite the observational associations, randomised controlled trials of vitamin D supplementation haven’t shown clear cognitive benefits.

A Cochrane review examined trials of vitamin D supplementation in people without baseline deficiency and found no effect on cognitive function [10]. The VITAL study, which followed more than 25,000 participants for over five years, found that vitamin D supplementation (2,000 IU daily) did not reduce the risk of dementia [11].

There are ongoing trials in people with confirmed vitamin D deficiency, which might show different results. Supplementation may only help those who are genuinely deficient, but we don’t know yet.

My honest take: maintaining adequate vitamin D levels is sensible for overall health, but I wouldn’t take vitamin D supplements specifically expecting them to prevent dementia. The evidence isn’t there yet. If your levels are deficient (your GP can test this), correcting the deficiency makes sense for multiple reasons, but don’t expect cognitive miracles.

For more detailed information about vitamin D, see our comprehensive vitamin D article.

3. Omega-3 fatty acids

Omega-3 fatty acids, particularly DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), are structural components of brain cell membranes. DHA makes up about 10-20% of total brain fatty acids, concentrated in grey matter. So researchers have naturally wondered whether supplementing with omega-3s might protect against cognitive decline.

Observational findings

People who eat more fish tend to have lower rates of dementia. The Rotterdam Study found that moderate fish consumption (eating fish at least once a week) was associated with a 60% lower risk of dementia over roughly two years of follow-up [12]. Similar associations have been found in other population studies.

Again, though, people who eat more fish probably differ from those who don’t in ways beyond omega-3 intake. They may have healthier overall diets, higher education levels, or better access to healthcare.

Clinical trial results

When researchers have actually tested omega-3 supplements in randomised trials, the results have been largely disappointing.

A Cochrane review of three trials involving 632 cognitively healthy participants found no difference in cognitive function between those taking omega-3 supplements and those taking placebo over 6-40 months [13]. The MAPT study in France found that omega-3 supplementation alone did not slow cognitive decline in older adults at risk of dementia [14].

For people who already have mild Alzheimer’s disease, a systematic review found no benefit from omega-3 supplementation on cognitive function or functional abilities [15].

There’s one potential exception. Some evidence suggests that omega-3 supplementation might benefit people in the very early stages of cognitive impairment, before dementia is established. The LipiDiDiet trial found that a specific multi-nutrient formulation containing omega-3s slowed brain atrophy and functional decline in prodromal Alzheimer’s disease [16]. But this was a combination product, so it’s unclear how much the omega-3 component specifically contributed.

My assessment

Eating oily fish a couple of times a week is reasonable dietary advice for general health. However, I wouldn’t recommend omega-3 supplements specifically for dementia prevention or treatment. The trial evidence doesn’t support it.

For more on omega-3 research, see our fish oil article.

What actually might help

Given the disappointing supplement data, what does the evidence suggest for dementia prevention?

The strongest evidence supports lifestyle factors. Regular exercise shows up repeatedly in the research. So does staying socially connected and managing cardiovascular risk factors like blood pressure and blood sugar. Getting decent sleep matters. Not smoking helps. None of this is surprising, but it’s also not what people want to hear when they’re looking for a pill [3].

The Mediterranean diet pattern, which includes olive oil, fish, vegetables, fruits, nuts, and legumes while limiting red meat and processed foods, has shown associations with better cognitive outcomes in observational studies [17]. Whether this is due to specific nutrients or the overall dietary pattern remains unclear.

For people already experiencing frequent urination or other symptoms that disrupt sleep, addressing these issues might indirectly benefit cognitive function by improving sleep quality.

The bottom line

I understand why people want a supplement solution for dementia. Watching cognitive decline in yourself or someone you love is devastating, and conventional treatments offer limited benefit.

Based on the current evidence:

Ginkgo biloba may modestly improve behavioural symptoms in people who already have dementia, but the prevention trials were negative. It won’t stop dementia from developing.

Vitamin D deficiency correlates with higher dementia risk in observational studies, but when researchers actually run trials giving people supplements, the cognitive benefits don’t materialise. If you’re genuinely deficient, correcting that makes sense for other reasons.

Omega-3 fatty acids are structural components of the brain, but supplementation trials have been consistently disappointing, both in healthy older adults and those with early Alzheimer’s.

I know this isn’t what people want to hear. The most effective approaches to reducing dementia risk are the boring lifestyle ones: stay active, stay connected to other people, keep your blood pressure and blood sugar under control, sleep properly, don’t smoke.

References

World Health Organization. Dementia fact sheet. WHO. 2023. Available from: https://www.who.int/news-room/fact-sheets/detail/dementia
NHS. Dementia guide. NHS. 2024. Available from: https://www.nhs.uk/conditions/dementia/
Livingston G, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Lancet. 2020;396(10248):413-446. PMID: 32738937
von Gunten A, et al. Efficacy of Ginkgo biloba extract EGb 761 in dementia with behavioural and psychological symptoms: A systematic review. World J Biol Psychiatry. 2016;17(8):622-633. PMID: 26223956
Vellas B, et al. Long-term use of standardised Ginkgo biloba extract for the prevention of Alzheimer’s disease (GuidAge): a randomised placebo-controlled trial. Lancet Neurol. 2012;11(10):851-859. PMID: 22959217
DeKosky ST, et al. Ginkgo biloba for prevention of dementia: a randomized controlled trial. JAMA. 2008;300(19):2253-2262. PMID: 19017911
Mei N, et al. Review of Ginkgo biloba-induced toxicity, from experimental studies to human case reports. J Environ Sci Health C. 2017;35(1):1-28. PMID: 28055331
Chai B, et al. Vitamin D deficiency as a risk factor for dementia and Alzheimer’s disease: an updated meta-analysis. BMC Neurol. 2019;19(1):284. PMID: 31722673
Navale SS, et al. Vitamin D and brain health: an observational and Mendelian randomization study. Am J Clin Nutr. 2022;116(2):531-543. PMID: 35348578
Rutjes AW, et al. Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life. Cochrane Database Syst Rev. 2018;12(12):CD011906. PMID: 30556597
Manson JE, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. N Engl J Med. 2019;380(1):33-44. PMID: 30415629
Kalmijn S, et al. Dietary fat intake and the risk of incident dementia in the Rotterdam Study. Ann Neurol. 1997;42(5):776-782. PMID: 9392577
Burckhardt M, et al. Omega-3 fatty acids for the treatment of dementia. Cochrane Database Syst Rev. 2016;4(4):CD009002. PMID: 27063583
Andrieu S, et al. Effect of long-term omega 3 polyunsaturated fatty acid supplementation with or without multidomain intervention on cognitive function in elderly adults with memory complaints (MAPT): a randomised, placebo-controlled trial. Lancet Neurol. 2017;16(5):377-389. PMID: 28359749
Araya-Quintanilla F, et al. Effectiveness of omega-3 fatty acid supplementation in patients with Alzheimer disease: A systematic review and meta-analysis. Neurologia (Engl Ed). 2020;35(2):105-114. PMID: 28993009
Soininen H, et al. 36-month LipiDiDiet multinutrient clinical trial in prodromal Alzheimer’s disease. Alzheimers Dement. 2021;17(1):29-40. PMID: 32920957
Loughrey DG, et al. The Impact of the Mediterranean Diet on the Cognitive Functioning of Healthy Older Adults: A Systematic Review and Meta-Analysis. Adv Nutr. 2017;8(4):571-586. PMID: 28710144