Dietary Supplements and Cognitive Function, Dementia, and Alzheimer’s Disease: What the Science Says
Clinical Guidelines, Scientific Literature, Info for Patients:
Dietary Supplements and Cognitive Function, Dementia, and Alzheimer’s Disease
There’s no conclusive evidence that Ginkgo biloba is efficacious in preventing or slowing dementia or cognitive decline.
There have been many randomized controlled trials examining the efficacy of Ginkgo biloba for cognitive function and dementia, including Alzheimer’s disease.
- A large, placebo-controlled, randomized clinical trial studying the well-characterized ginkgo product EGb-761 in more than 3,000 older adults found it ineffective in lowering the overall incidence of dementia and Alzheimer’s disease. Further analysis of the same data also found ginkgo to be ineffective in slowing cognitive decline, lowering blood pressure, or reducing the incidence of hypertension.
- However, a 2015 systematic review and meta-analysis involving a total of 2,561 participants concluded that Ginkgo biloba EGb-761 at 240 mg/day stabilized or slowed decline in cognition, function, behavior, and global change at 22 to 26 weeks in cognitive impairment and dementia, especially for people with neuropsychiatric symptoms.
- Another 2016 systematic review and meta-analysis of 21 randomized controlled trials involving 2,608 participants concluded that Ginkgo biloba is potentially beneficial for improving cognitive function, activities of daily living, and global clinical assessment in people with mild cognitive impairment or Alzheimer’s disease; however, because of small sample size, inconsistent findings and methodological quality of studies included in the review, more research is need to confirm the effectiveness and safety of Ginkgo biloba for the treatment of cognitive impairment and Alzheimer’s disease.
- Side effects of ginkgo supplements may include headache, nausea, gastrointestinal upset, diarrhea, dizziness, or allergic skin reactions. More severe allergic reactions have occasionally been reported. There are some data to suggest that ginkgo can increase bleeding risk.
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.
There have been several randomized controlled trials and systematic reviews examining the efficacy of omega-3 fatty acid supplementation for dementia and Alzheimer’s disease.
- 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 people consumed. However, a 2016 Cochrane review of three randomized, placebo-controlled trials involving a total of 632 participants found no convincing evidence for the efficacy of omega-3 polyunsaturated fatty acid supplements in the treatment of mild to moderate Alzheimer’s disease. The result was consistent for all outcomes relevant for people with dementia.
- Further, a 2012 Cochrane review of three randomized controlled trials involving more than 3,500 participants concluded that available evidence shows no benefit of omega-3 supplementation on the cognitive functioning of older people without dementia.
- Omega-3 fatty acid supplements usually do not have negative side effects. When side effects do occur, they typically consist of minor gastrointestinal symptoms. Omega-3 supplements may extend bleeding time. People who take anticoagulants or nonsteroidal anti-inflammatory drugs should use caution.
A recent 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.
Many laboratory and animal studies have investigated the role of vitamin E in the prevention and treatment of Alzheimer’s disease; evidence from human studies is much more limited.
- A 2017 Cochrane review of two randomized controlled trials involving a total of 820 participants with either mild cognitive impairment or Alzheimer’s disease found no evidence the alpha-tocopherol form of 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. The researchers noted that these findings are still based on small numbers of trials and participants and further research is quite likely to affect the results.
- Research has not found any adverse effects from consuming vitamin E in food. However, high doses of alpha-tocopherol supplements can cause hemorrhage and interrupt blood coagulation in animals, and in vitro data suggest that high doses inhibit platelet aggregation.
- Recent results from the Selenium and Vitamin E Cancer Prevention (SELECT) Trial suggest that vitamin E supplements (400 IU/day) may increase the risk of prostate cancer. Follow-up studies exploring this finding are underway.
- Vitamin E supplements have the potential to interact with several types of medications, including anticoagulant and antiplatelet medications, simvastatin and niacin, and chemotherapy and radiotherapy.
There have only been a few clinical trials examining the effects of curcumin on cognitive function and Alzheimer’s disease, so there aren’t enough data to support the use of curcumin for this condition.
A few preliminary clinical studies exploring the effects of curcumin on Alzheimer’s disease have been conducted.
- A 2016 12-month, randomized, placebo-controlled trial involving 96 community-dwelling, cognitively healthy, older adults found that curcumin had limited influence on cognitive function, mood, or general quality of life over 12 months. The researchers concluded that additional longitudinal studies are warranted to determine whether curcumin can slow neurodegeneration leading to cognitive decline and Alzheimer’s disease.
- Curcumin is considered safe for most adults, but high doses or long-term use may cause indigestion, nausea, or diarrhea.
- In animals, very high doses of curcumin have caused liver problems. No cases of liver problems have been reported in people.
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.
- 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.
- 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.
- 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.
- 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.
- 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.
NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.
The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH’s Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH Web site at nccih.nih.gov. NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.
Content is in the public domain and may be reprinted, except if marked as copyrighted (©). Please credit the National Center for Complementary and Integrative Health as the source. All copyrighted material is the property of its respective owners and may not be reprinted without their permission.