Can Fish Oil Prevent Alzheimer's Disease and Dementia?

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Omega-3 fatty acids, including alpha-linoleic acid (ALA) and docosahexaenoic acid (DHA), are essential fats that cannot be made naturally by the human body, and must be obtained from dietary sources. Omega-3 fatty acids are found in certain plant species such as flax, chia, and canola. Since they are also present in fish and algae, fish oil is a good dietary source of omega-3 fatty acids. These fatty acids are associated with multiple health effects, including reduction of inflammatory activity, healthy fetal development, and prevention of cardiac disease. Scientists have also explored whether omega-3 fatty acids can affect the development of dementia, including Alzheimer’s disease.

Alzheimer’s disease is the most common cause of dementia and affects more than 44 million people worldwide. While the exact cause of Alzheimer’s disease is unknown, genetic factors may play a role. The apolipoprotein (APOE) gene, which has several variants, is a known risk factor for Alzheimer’s disease. One APOE gene variant, the e4 allele, significantly increases the risk of developing Alzheimer’s disease. People who possess one of these e4 variants are three times more likely to develop Alzheimer’s disease than the general population, and those with two e4 alleles are 12 times more likely to develop Alzheimer’s. However, this is not the only trait that affects the likelihood of developing Alzheimer’s disease, and there are likely multiple other genetic factors that influence whether an individual is susceptible to developing the disorder. While some of these genetic characteristics are currently known, others remain to be discovered.

Brain inflammation is also associated with the development of Alzheimer’s disease, and factors that affect brain inflammation may also impact a person’s likelihood of being diagnosed with Alzheimer’s disease. Since omega-3 fatty acids are associated with anti-inflammatory effects, researchers have explored the question of whether omega-3 fatty acid supplementation can be used to prevent the onset of Alzheimer’s disease. Several studies suggest that omega-3 supplementation may be helpful in preventing the development of Alzheimer’s disease, especially in people who have the e4 variant of the APOE gene. However, in people who were already diagnosed with Alzheimer’s disease, omega-3 supplementation did not affect the progression of memory decline.

A recent study in the journal Nutrients explored the relationship between the presence of an omega-3 fatty acid in the blood (called “red blood cell DHA”) and dementia. This study involved 1,490 older individuals (greater than 65 years of age) from Framingham, Massachusetts, who did not have a history of dementia. These study participants underwent a blood draw to determine their level of red blood cell DHA. The individuals were then followed for up to 14 years and monitored for the development of dementia. Researchers found that the study participants who initially had a higher red blood cell DHA level ended up having a 49% lower risk of developing Alzheimer’s disease. For those study participants with the e4 variant of the APOE gene, those who had higher red blood cell DHA also had a significantly decreased risk of developing Alzheimer’s disease.

The results of this study seem to indicate that people who have higher DHA levels in their body may have a reduced risk of developing dementia, especially if they have the APOE e4 gene variant. This may mean that for some people, omega-3 fatty acid supplementation with DHA may be helpful in preventing the onset of Alzheimer’s disease. While intriguing, there are several limitations to this study that need to be considered when interpreting its results. First, since the exact known cause of Alzheimer’s disease remains unknown, the best way to prevent the disease is also unclear. DHA supplementation may be helpful, but there are likely other environmental and genetic factors involved. Second, even though omega-3 fatty acid supplementation is associated with multiple health benefits, the optimal dose and duration of supplementation needed to achieve these beneficial health effects is unclear. Third, this study was performed in a specific subset of patients and only included older individuals. Additional studies are needed to verify whether these study results are applicable to younger individuals or other populations.

Many people choose to take omega-3 fatty acids as dietary supplements due to their reported health benefits, but it’s important to know that the dietary supplement industry is not as carefully regulated as the pharmaceutical industry. Some omega-3 fatty acid supplements have been recalled due to contamination with other medications. Omega-3 fatty acid supplements derived from fish may contain mercury, dioxins, polychlorinated biphenyls (PCBs), or other unwanted contaminants. Fish oil preparations may cause adverse effects including nausea, belching, and diarrhea. Because of these concerns, some people prefer to obtain omega-3 fatty acids from dietary sources. There are also vegan and vegetarian omega-3 fatty supplements available that are derived from algae and other non-fish sources.

For questions about adverse reactions from the use of dietary supplements, including omega-3 fatty acids, contact poison control for expert advice. Get an immediate personalized recommendation online or call 1-800-222-1222. Both options are free, confidential, and available 24 hours a day.

Kelly Johnson-Arbor, MD
Medical Toxicologist