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NCCIH Clinical Digest

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Dietary Supplements and Cognitive Function, Dementia, and Alzheimer’s Disease: What the Science Says

November 2020

Clinical Guidelines, Scientific Literature, Info for Patients: 
Dietary Supplements and Cognitive Function, Dementia, and Alzheimer’s Disease

A senior Hispanic man in his 80s sitting in a wheelchair, talking to his adult daughter, who is in her 30s, pushing the wheelchair from behind. They are walking in a city park in fall, building out of focus in the background.

Ginkgo biloba

There’s no conclusive evidence that Ginkgo biloba is efficacious in preventing or slowing dementia or cognitive decline.


Among the nutritional and dietary factors studied to prevent cognitive decline in older adults, the most consistent positive research findings are for omega-3 fatty acids, often measured as how much fish is consumed in the diet. However, several high-quality reviews have found no convincing evidence for the efficacy of omega-3 polyunsaturated fatty acid supplements in the treatment of mild-to-moderate Alzheimer’s disease.

Vitamin E

A 2017 Cochrane systematic review found no evidence that vitamin E given to people with mild cognitive impairment prevents progression to dementia, or that it improves cognitive function in people with mild cognitive impairment or dementia due to Alzheimer’s disease. However, there is moderate quality evidence from a single study that it may slow functional decline in Alzheimer’s disease.


Preclinical studies have shown that curcumin targets inflammatory and antioxidant pathways as well as (directly) amyloid aggregation. However, the few clinical trials that have examined the effects of curcumin on Alzheimer’s disease are limited and inconsistent, making it difficult to draw conclusions about potential benefits.

Vitamin B

Findings from short-term studies suggest that B-vitamin supplements (B12, B6, and folic acid) do not help cognitive functioning in adults age 50 or older with or without dementia.

Other Natural Products

  • Research has shown that taking a multivitamin or high doses of individual vitamins, such as selenium, B vitamins, and calcium and vitamin D, doesn’t have any clear benefits for cognition in well-nourished people.
    • Excessive selenium intake, or selenosis, may result in hair and nail loss or brittleness, lesions of the skin and nervous system, nausea, diarrhea, skin rashes, mottled teeth, fatigue, irritability, and nervous system abnormalities.
    • Excessively high levels of calcium in the blood known as hypercalcemia can cause renal insufficiency, vascular and soft tissue calcification, hypercalciuria (high levels of calcium in the urine), and kidney stones. High calcium intake can cause constipation.
    • Excess amounts of vitamin D are toxic. Because vitamin D increases calcium absorption in the gastrointestinal tract, vitamin D toxicity results in marked hypercalcemia, hypercalciuria, and high serum 25(OH)D levels.
  • Although melatonin may help promote sleep in healthy people, a 2014 Cochrane review of two studies found no evidence that melatonin, either immediate- or slow-release, improved any major sleep outcome in patients with Alzheimer’s disease.
    • For melatonin supplements, particularly at doses higher than what the body normally produces, there’s not enough information yet about possible side effects to have a clear picture of overall safety. Short-term use of melatonin supplements appears to be safe for most people, but information on the long-term safety of supplementing with melatonin is lacking.
  • Coconut oil to prevent or treat Alzheimer’s disease is of interest to researchers; however, only small clinical trials have been conducted to date, and the use of coconut oil for Alzheimer’s disease is not supported by any large, rigorous clinical data.
    • Coconut oil supplements appear to be safe when used in the short term (doses of 10 mL two or three times daily for up to 12 weeks).


  • Burckhardt M, Herke M, Wustmann T, et al. Omega-3 fatty acids for the treatment of dementia. Cochrane Database Syst Rev. 2016;4:CD009002.
  • DeKosky ST, Williamson JD, Fitzpatrick AL, et al. Ginkgo biloba for prevention of dementia: a randomized controlled trial. JAMA. 2008;300(19):2253-2262.
  • Farina N, Llewellyn D, Isaac MG, et al. Vitamin E for Alzheimer’s dementia and mild cognitive impairment. Cochrane Database Syst Rev. 2017;1:CD002854.
  • Fernando WM, Martins IJ, Goozee KG, et al. The role of dietary coconut for the prevention and treatment of Alzheimer’s disease: potential mechanisms of action. Br J Nutr. 114(1):1-14.
  • Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011;306(14):1549–1556.
  • McCleery J, Cohen DA, Sharpley AL. Pharmacotherapies for sleep disturbances in Alzheimer’s disease. Cochrane Database Syst Rev. 2014;3:CD009178.
  • McCleery J, Cohen DA, Sharpley AL. Pharmacotherapies for sleep disturbances in Alzheimer’s disease. Cochrane Database Syst Rev. 2014;3:CD009178.
  • Rainey-Smith SR, Brown BM, Sohrabi HR, et al. Curcumin and cognition: a randomized, placebo-controlled, double-blind study of community dwelling older adults. Br J Nutr. 115(12):2106-2113.
  • Snitz BE, O’Meara ES. Carlson MC, et al. Ginkgo biloba for preventing cognitive decline in older adults: a randomized trial. JAMA. 2009;302(24):2662-2670.
  • Sydenham E, Dangour AD, Lim W-S. Omega 3 fatty acid for the prevention of cognitive decline and dementia. Cochrane Database Syst Rev. 2012:6:CD005379.
  • Tan MS, Yu JT, Tan CC, et al. Efficacy and adverse effects of ginkgo biloba for cognitive impairment and dementia: a systematic review and meta-analysis. J Alzheimers Dis. 2015;43(2):589-603.
  • Voulgaropoulou SD, van Amelsvoort TAMJ, Prickaerts J, et al. The effect of curcumin on cognition in Alzheimer’s disease and healthy aging: a systematic review of pre-clinical and clinical studies. Brain Res. 2019;1725:146476.
  • Yang G, Wang Y, Sun J, et al. Ginkgo biloba for mild cognitive impairment and Alzheimer’s disease: a systematic review and meta-analysis of randomized controlled trials. Curr Top Med Chem. 2016;16(5):520-528.

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