A decline in DHA levels has been observed in Alzheimer’s patients in areas of the brain associated with cognition and memory, namely the hippocampus and frontal cortex. A diet rich in omega-3 fatty acids (rich in DHA; fish oils) could therefore be beneficial in restoring cognitive performance and brain function.
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What is Omega-3?
Omega-3 is a group of polyunsaturated fatty acids which are important for the normal functioning of the body and for optimal health. There are 3 primary omega-3 fatty acids: docosahexaenoic acid (DHA) & eicosapentaenoic acid (EPA) found in fish and seafood oils, as well as α-linoleic acid (ALA) which is found in plant oils e.g. flaxseed oil and walnut oil.
Humans (among other mammals) are unable to produce omega-3 fatty acids naturally and must acquire them through our diet. Within the brain, DHA is the most important and abundant fatty acid and is needed for neuronal health, synaptic transmission and membrane integrity.
Is there any evidence for Omega-3 supplements preventing Alzheimer’s disease?
Animal studies have shown that omega-3 supplementation can lower total beta-amyloid levels in the brain. Furthermore, some studies have shown an improvement in cognition after omega-3 supplementation compared to those without.
However, the majority of these studies investigated long-term omega-3 supplementation over a prolonged period (>10 years). Therefore, long-term supplementation prior to advanced-disease stage progression is essential.
On the other hand omega-3 supplements may be beneficial if taken earlier in life before disease onset when there is only a mild cognitive impairment (mimicking animal study findings).
Despite this finding, no statistically significant differences have been observed between those on omega-3 supplements and those on placebo tablets. Furthermore, a beneficial effect on cognition is known only to occur in a few assessment criteria, and not global cognitive function overall.
It is important to note, however, that some studies added olive oil to their placebos, and since olive oil is known to be beneficial to health, the trials actually tested omega-3 supplements against other lipid supplements rather than against totally inert placebos. In such a situation, any significant results that could have arisen would actually be dampened by the use of active placebos.
Can Omega-3 help treat or prevent Alzheimer’s disease?
Omega-3 supplements may be useful to some extent in cardiovascular health if taken regularly and from an early stage in life, although more concrete evidence is required to support this.
As to their role in the treatment of Alzheimer’s disease, there is no significant evidence in this area, especially when the disease has progressed to a moderate to severe stage. However, some studies suggest a weak beneficial effect, namely, a mild slowing down of the onset of Alzheimer’s disease if omega-3 is taken when symptoms are only mild.
As with any observational study looking at the effects of natural or herbal supplements in the treatment or prevention of disease, more randomized controlled studies are essential, with sufficiently large sample sizes.
For instance, the ingestion of other medications has not been tested for in any of the patients involved in the studies. These patients were probably taking other approved AD-medications, and therefore any beneficial effects may actually be attributed to these drugs.
Summary
Any conclusions drawn from observational studies with small cohorts and weak associations cannot be taken as solid evidence. Nonetheless, there is no harm in taking omega-3 supplements for improved health, and it may in part be beneficial to delaying the progression of dementia. Animal studies have shown a significant improvement in Alzheimer’s pathology and cognitive abilities with long-term omega-3 supplementation.
Further Reading
The molecular underpinnings by which traumatic brain injury increases Alzheimer's disease risk