Docosahexaenoic acid (DHA)


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Name: Docosahexaenoic acid (DHA)
Synonyms: Omega 3 fatty acid
Therapy Type: Supplement, Dietary (timeline)
Target Type: Other (timeline)
Condition(s): Alzheimer's Disease
U.S. FDA Status: Alzheimer's Disease (Phase 4)
Company: Martek Biosciences Corporation, NeuroBioPharm, Inc.


Docosahexaenoic acid (DHA) is one of the most abundant polyunsaturated fatty acids in the human brain. Epidemiological research has linked high DHA consumption with a lower risk of Alzheimer's disease (e.g., Morris et al., 2003). People ingest DHA from foods such as fatty fish, walnuts, or flax seeds, or from dietary supplements. These are being marketed in different formulations of DHA, or DHA mixed with other omega-3 fatty acids such as eicosapentaenoic acid (EPA). Elevated blood levels of DHA correlate with reduced dementia risk in some but not all studies (Schaefer et al., 2006; Laurin et al., 2003). Animal studies have reported a reduction of amyloid, tau, and neuritic pathology with oral intake of DHA (Lim et al., 2005Green et al., 2007; Calon et al., 2004).


DHA has been tested in clinical trials by itself and as part of other food-supplement formulations.

In 2000, Karolinska University Hospital began the OmegAD trial, which evaluated a six-month course of treatment with a DHA-containing fish oil formulation called EPAX 1050 TG in 204 people with mild to moderate AD, of whom 174 completed the study. The treatment and placebo groups did not differ on either of the main outcome measures, decline on the MMSE and ADAS-cog, or on neuropsychiatric symptoms overall. However, analysis of a small subgroup of the 32 mildest cases did suggest less decline on the MMSE, though not ADAS-cog, and a similar slowing of decline appeared to occur in the placebo group once switched to DHA after six months (Freund-Levi et al., 2006; see news and commentaryFreund-Levi et al., 2008). Substudies suggested that DHA treatment increased CSF levels of DHA and other fatty acids and decreased levels of tau, as well as changing expression of inflammation-related genes and release of certain cytokines in white blood cells (Freund-Levi et al., 2014; Vedin et al., 2012; Vedin et al., 2008).

From 2007 to 2009, the Alzheimer's Disease Cooperative Study conducted a study at 51 centers in North America to evaluate an 18-month course of 2 grams per day of DHA in 402 patients with mild to moderate AD, of whom 295 completed the trial. DHA had no effect, relative to placebo, on rate of decline on either the ADAS-cog or the CDR-SOB clinical/functional assessment. Analysis by participants' ApoE genotype indicated a slower cognitive decline in ApoE4 noncarriers, who may have been relatively less advanced in their disease (Quinn et al., 2010Nov 2010 news).

This pharmacogenetic hint of a differential effect prompted several bioavailability studies at the Université de Sherbrooke, Quebec, Canada, between 2009 and 2011, which analyzed the percentage of DHA in lipoproteins, incorporation into plasma lipids, and pharmacokinetics by ApoE genotype in healthy young adults and people with MCI (e.g., Chouinard-Watkins et al., 2013Plourde et al., 2014).

The largest clinical trial of DHA is MAPT, conducted in four cities in France. This three-year, secondary prevention study in 1,680 participants began in 2008 and enrolled people 70 and older who reported a subjective memory complaint and a mild functional loss, were frail and walked slowly, but did not meet an Alzheimer's diagnosis (Carrié et al., 2012). MAPT compared three interventions—800 mg DHA and 225 mg EPA daily alone, DHA/EPA plus a multidomain behavioral intervention, multidomain behavioral intervention alone—to placebo (Gillette-Guyonnet et al., 2009). Neither intervention, alone or in combination, significantly slowed cognitive decline as measured by a composite score of four tests of recall, orientation, processing and verbal fluency (Andrieu et al., 2017). An amyloid PET substudy compared the effects of the multidomain intervention and DHA/EPA according to brain amyloid status. The multidomain intervention, with or without DHA/EPA, improved composite scores after 36 months compared to placebo in the amyloid positive, but not negative, subset; DHA/EPA alone had no effect in either subset (Delrieu et al., 2019). In another PET analysis, cortical amyloid was lower after two years in people who got the multidomain intervention, with or without DHA/EPA, but not in those who received DPA/EPA alone (Hooper et al., 2020).

A subsequent analysis of MAPT data suggested higher odds of cognitive decline for people with low DHA/EPA levels (Bowman et al., 2019). Lower serum DHA was also correlated with more cerebral amyloidosis and atrophy (Yassine et al., 2016Aug 2016 news). In response to those findings, MAPT investigators in April 2018 began LO-MAPT. This 18-month study is enrolling 400 older adults with low DHA/EPA status, who will be randomized to 1.53 g/day DHA/EPA or placebo. Participants must have subjective memory complaints or a family history of AD. The primary outcome is change in a cognitive composite of scores on the Free Cued and Selective Reminding Test, MMSE, and Category Naming Test. The trial offers an 18-month open-label extension, and will end in 2022.

From 2009 to 2011, the company NeuroBioPharm Inc. ran a six-month trial at 14 different sites in Canada to compare soft-capsule formulations of fish oil and krill oil, each containing 100 mg DHA, to placebo in 175 people with mild to moderate Alzheimer's disease. Krill oil contains DHA and EPA in a form claimed to be more bioavailable than fish oil (e.g. Schuchardt et al., 2011). This trial used the Neuropsychological Test Battery as primary outcome; data have not been published.

One DHA study, at Oregon Health and Science University, started in May 2014. According to published baseline data, the trial recruited 102 people age 75 and older who were cognitively impaired but did not have dementia, and suboptimal blood levels of DHA and EPA of less than 110 ug/ml. Participants were randomized to receive a three-year course of 1.65 grams/day of EPA plus DHA or soybean oil placebo (Bowman et al., 2019). Seeking to understand DHA's effect on vascular cognitive aging, this trial used white-matter hyperintensity as primary outcome; secondary and other outcome measures included other brain imaging modalities as well as blood-based indicators of endothelial health and neuropsychological tests. Top-line results were presented at the 2020 CTAD. Supplementation failed to slow accumulation of white-matter hyperintensities in the 45 placebo and 42 treated participants who had a least one follow-up MRI. At the end of the study, 24 of the treatment group had plasma DHA+EPA levels greater than 110 ug/ml. In a prespecified analysis, this group had fewer white-matter hyperintensities and maintained better white-matter integrity than the placebo group. There were no differences in total brain volume, ventricular volume, medial temporal lobe atrophy, excessive cognitive functions, or adverse events.

In June 2016, a pilot study at the University of Southern California began evaluating how much of a DHA supplement enters the central nervous system, and whether CSF levels are influenced by ApoE4 status (for review, see Yassine et al., 2017). The trial enrolled 31 adults older than 55 with a family history of dementia, who took 2g DHA per day or placebo for 26 weeks. The primary outcome was change in CSF DHA before and after supplementation. According to published results, this dose of DHA resulted in a 200 percent increase in plasma DHA compared to placebo, but only a 28 percent increase in CSF DHA (Arellanes et al., 2020). ApoE4 carriers had slightly lower CSF DHA. For EPA, CSF levels increased 43 percent, but were significantly lower in ApoE4 carriers than in noncarriers. Other endpoints including brain volume and cognitive scores did not differ between supplement and placebo groups.

In July 2018, the same group began a larger follow-up study in 320 healthy adults age 60-80, who have at least one dementia risk factor. Participants will take 2g DHA or placebo daily for two years. After six months of treatment, investigators will analyze CSF fatty acids; changes in MRI measures of structural and functional connectivity and cognition will be assessed at two years. The study will run through 2023.

For details of clinical trials of DHA in Alzheimer's, see

Last Updated: 02 Feb 2021


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News Citations

  1. First Trial of Fish Fats Shows Promise for Early AD
  2. Paper Alert: Negative DHA Trial Fuels Soul-Searching in AD Field
  3. Less Salmon, More Plaques? Link Between Omega-3s and Aβ Reinvigorates Fish Oil Debate

Paper Citations

  1. . Omega-3 fatty acid treatment in 174 patients with mild to moderate Alzheimer disease: OmegAD study: a randomized double-blind trial. Arch Neurol. 2006 Oct;63(10):1402-8. PubMed.
  2. . Omega-3 supplementation in mild to moderate Alzheimer's disease: effects on neuropsychiatric symptoms. Int J Geriatr Psychiatry. 2008 Feb;23(2):161-9. PubMed.
  3. . Transfer of omega-3 fatty acids across the blood-brain barrier after dietary supplementation with a docosahexaenoic acid-rich omega-3 fatty acid preparation in patients with Alzheimer's disease: the OmegAD study. J Intern Med. 2014 Apr;275(4):428-36. Epub 2014 Jan 11 PubMed.
  4. . Effects of DHA-rich n-3 fatty acid supplementation on gene expression in blood mononuclear leukocytes: the OmegAD study. PLoS One. 2012;7(4):e35425. Epub 2012 Apr 24 PubMed.
  5. . Effects of docosahexaenoic acid-rich n-3 fatty acid supplementation on cytokine release from blood mononuclear leukocytes: the OmegAD study. Am J Clin Nutr. 2008 Jun;87(6):1616-22. PubMed.
  6. . Docosahexaenoic acid supplementation and cognitive decline in Alzheimer disease: a randomized trial. JAMA. 2010 Nov 3;304(17):1903-11. PubMed.
  7. . Disturbance in uniformly 13C-labelled DHA metabolism in elderly human subjects carrying the apoE ε4 allele. Br J Nutr. 2013 Apr 30;:1-9. PubMed.
  8. . Kinetics of 13C-DHA before and during fish-oil supplementation in healthy older individuals. Am J Clin Nutr. 2014 May 14;100(1):105-112. PubMed.
  9. . Recruitment strategies for preventive trials. The MAPT study (MultiDomain Alzheimer Preventive Trial). J Nutr Health Aging. 2012 Apr;16(4):355-9. PubMed.
  10. . Commentary on "A roadmap for the prevention of dementia II. Leon Thal Symposium 2008." The Multidomain Alzheimer Preventive Trial (MAPT): a new approach to the prevention of Alzheimer's disease. Alzheimers Dement. 2009 Mar;5(2):114-21. PubMed.
  11. . 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 May;16(5):377-389. Epub 2017 Mar 27 PubMed.
  12. . Multidomain intervention and/or omega-3 in nondemented elderly subjects according to amyloid status. Alzheimers Dement. 2019 Nov;15(11):1392-1401. Epub 2019 Sep 23 PubMed.
  13. . Cortical β-Amyloid in Older Adults Is Associated with Multidomain Interventions with and without Omega 3 Polyunsaturated Fatty Acid Supplementation. J Prev Alzheimers Dis. 2020;7(2):128-134. PubMed.
  14. . A blood-based nutritional risk index explains cognitive enhancement and decline in the multidomain Alzheimer prevention trial. Alzheimers Dement (N Y). 2019;5:953-963. Epub 2019 Dec 28 PubMed. Correction.
  15. . Association of Serum Docosahexaenoic Acid With Cerebral Amyloidosis. JAMA Neurol. 2016 Oct 1;73(10):1208-1216. PubMed.
  16. . Incorporation of EPA and DHA into plasma phospholipids in response to different omega-3 fatty acid formulations--a comparative bioavailability study of fish oil vs. krill oil. Lipids Health Dis. 2011 Aug 22;10:145. PubMed.
  17. . Randomized Trial of Marine n-3 Polyunsaturated Fatty Acids for the Prevention of Cerebral Small Vessel Disease and Inflammation in Aging (PUFA Trial): Rationale, Design and Baseline Results. Nutrients. 2019 Mar 29;11(4) PubMed.
  18. . Association of Docosahexaenoic Acid Supplementation With Alzheimer Disease Stage in Apolipoprotein E ε4 Carriers: A Review. JAMA Neurol. 2017 Mar 1;74(3):339-347. PubMed.
  19. . Brain delivery of supplemental docosahexaenoic acid (DHA): A randomized placebo-controlled clinical trial. EBioMedicine. 2020 Sep;59:102883. Epub 2020 Jul 17 PubMed.
  20. . Consumption of fish and n-3 fatty acids and risk of incident Alzheimer disease. Arch Neurol. 2003 Jul;60(7):940-6. PubMed.
  21. . Plasma phosphatidylcholine docosahexaenoic acid content and risk of dementia and Alzheimer disease: the Framingham Heart Study. Arch Neurol. 2006 Nov;63(11):1545-50. PubMed.
  22. . Omega-3 fatty acids and risk of cognitive impairment and dementia. J Alzheimers Dis. 2003 Aug;5(4):315-22. PubMed.
  23. . A diet enriched with the omega-3 fatty acid docosahexaenoic acid reduces amyloid burden in an aged Alzheimer mouse model. J Neurosci. 2005 Mar 23;25(12):3032-40. PubMed.
  24. . Dietary docosahexaenoic acid and docosapentaenoic acid ameliorate amyloid-beta and tau pathology via a mechanism involving presenilin 1 levels. J Neurosci. 2007 Apr 18;27(16):4385-95. PubMed.
  25. . Docosahexaenoic acid protects from dendritic pathology in an Alzheimer's disease mouse model. Neuron. 2004 Sep 2;43(5):633-45. PubMed.

External Citations


Further Reading


  1. . Ageing and apoE change DHA homeostasis: relevance to age-related cognitive decline. Proc Nutr Soc. 2013 Oct 9;:1-7. PubMed.
  2. . Nutrition and neurodegeneration: epidemiological evidence and challenges for future research. Br J Clin Pharmacol. 2013 Mar;75(3):738-55. PubMed.
  3. . ω-3 fatty acids in the prevention of cognitive decline in humans. Adv Nutr. 2013 Nov;4(6):672-6. Epub 2013 Nov 6 PubMed.
  4. . Omega-3 polyunsaturated fatty acids in Alzheimer's disease: key questions and partial answers. Curr Alzheimer Res. 2011 Aug;8(5):470-8. PubMed.
  5. . Quantitative Erythrocyte Omega-3 EPA Plus DHA Levels are Related to Higher Regional Cerebral Blood Flow on Brain SPECT. J Alzheimers Dis. 2017;58(4):1189-1199. PubMed.
  6. . Long-chain omega-3 fatty acids improve brain function and structure in older adults. Cereb Cortex. 2014 Nov;24(11):3059-68. Epub 2013 Jun 24 PubMed.
  7. . A Randomized Placebo-Controlled Pilot Trial of Omega-3 Fatty Acids and Alpha Lipoic Acid in Alzheimer's Disease. J Alzheimers Dis. 2014 Jan 1;38(1):111-20. PubMed.
  8. . Brain targeting with docosahexaenoic acid as a prospective therapy for neurodegenerative diseases and its passage across blood brain barrier. Biochimie. 2020 Mar;170:203-211. Epub 2020 Jan 31 PubMed.
  9. . Role of phosphatidylcholine-DHA in preventing APOE4-associated Alzheimer's disease. FASEB J. 2019 Feb;33(2):1554-1564. Epub 2018 Oct 5 PubMed.
  10. . Long-chain omega-3 fatty acids and the brain: a review of the independent and shared effects of EPA, DPA and DHA. Front Aging Neurosci. 2015;7:52. Epub 2015 Apr 21 PubMed.