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Memory and Fish Oil

Fish oil is good for the health. Its health benefits are due to its omega-3 fatty acid content. The most popular omega-3 fatty acids found in fish are DHA and EPA. Different studies have found that fish oil can help improve the memory. Of the two omega-3 fatty acids found in fish oil, DHA is believed to provide the most benefits. How does DHA improve memory? Read on to find out.
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Fish oil is the oil derived from the tissues of fatty fish. Besides these fish, fish oil is also available as supplements.

The main content of fish oil are the omega-3 fatty acids: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These fatty acids are precursors of eicosanoids which are natural anti-inflammatory compounds produced in the body.

The fish from which fish oil is obtained do not really produce these omega-3 fatty acids. Rather, they are produced by other marine life such as microalgae which are consumed by fish.

The accumulation of these fatty acids in fish is also followed by the accumulation of mineral antioxidants such as selenium and iodide. These antioxidants stabilize fish oil and protect it from going bad from the oxidation of the polyunsaturated lipids they contain.

Fish oil supplements, on the other hand, employ small amounts of vitamin E to serve as the antioxidant stabilizing the oil. Other nutrients that may be found in fish oil supplements are vitamins A, B1, B2, B3, C and D as well as iron and calcium.

The accumulation of other compounds beyond fatty acid means that some of these fish also accumulate high amounts of toxins found in their marine environment. Some of the toxic compounds also accumulated in fish are mercury, PCBs and dioxin.

For this reason, big, fatty fish such as shark and swordfish are not recommended as dietary sources of omega-3 fatty acids and fish oil. Instead, smaller fatty fish such as salmon, sardines, mackerel, halibut, cod and tuna.

Health Benefits of Fish Oil

The omega-3 fatty acids, DHA and EPA, in fish oil are credited with a number of health benefits. Most of these benefits have been confirmed by different studies. However, in most cases the results of these studies are conflicting.

Fish oil may prevent heart attackOverall, there is some evidence that fish oil may prevent heart attack and reduce the risks of some cancers.

The omega-3 fatty acids definitely have anti-inflammatory properties, and they are therefore useful in the treatment of inflammatory diseases such as rheumatoid arthritis. Fish oil is also useful in the treatment of developmental disorders such as ADHD (attention deficit hyperactivity disorder).

Preliminary studies also indicate that fish oil may be effective in the treatment of mental disorders including depression.

Such studies have also been done on the effect of fish oil on dementia, cognitive decline and memory loss. The results suggests that fish may provide some benefits for some group of people experiencing memory loss.

DHA, for example, has been proven to promote neurogenesis (the production of new nerve cells) in the brain.

The Flip Side of Fish Oil

Fish oil is not the all-star natural remedy most people believe it is.

Besides the environmental toxins such as heavy metals, PCBs and dioxin that may accumulate in it, fish oil may also contain high levels of vitamin A and so cause symptoms of vitamin A toxicity.

Furthermore, taking fish oil supplements with blood thinners such as warfarin may cause excessive bleeding. The reduced clotted promoted by fish oil is also dangerous to people with bleeding disorders such as hemophilia.

In addition, it is easy to consume fish oil supplements excessively. This is because most people mistake the recommended dose of omega-3 for the recommended dose of fish oil.

The FDA recommends a maximum dose of 3 g per day of omega-3. This is not equivalent to 3 g of fish oil. Rather, 1 g of fish oil contains 0.3 g of omega-3.

If omega-3 fatty acids such as DHA and EPA are consumed in the excess of 3 g per day, they will cause:

  • Excessive bleeding and increase the risk of hemorrhagic stroke
  • Increased oxidative stress in the body from the free radicals formed from the oxidation of these fatty acids
  • Increased level of LDL (“bad” cholesterol) and other associated lipoproteins especially in people suffering from diabetes and hyperlipidemia
  • Poor control of blood sugar in diabetic patients

The Case for Fish Oil

In Young Animal Models

A 1999 study published in the journal, Neuroscience, investigated the effects of DHA on memory and learning in young rats.

The study design involved feeding 3 generations of Wistar rats with a diet devoid of fish oil. Then the young male rats of the third generation were divided into 2 groups. One group received 300 mg/kg/day of DHA dissolved in 5% gum Arabic for 10 weeks while the other group only received the gum Arabic.

The rats receiving DHA had a higher ratio of docosahexaenoic acid/arachidonic acid in their hippocampus and cerebral cortex. These are the 2 major parts of the brain involved in memory and learning.

The result showed that the increased concentration of DHA in the brain improved long-term or reference memory but had no effect on working or short-term memory.

This study not only demonstrates that DHA (and by extension, fish oil) can improve memory and learning but also that the docosahexaenoic acid/arachidonic acid ration in the hippocampus or cerebral cortex may be used as an indicator of learning ability.

Early Supplementation is Better

A 2008 study published in the Journal of Nutrition, however, arrived at a slightly different conclusion.

In this study, fish oil supplement was used instead of DHA. In addition, some of the rats involved in the study were kept fatty acid-deficient from birth to day 140 when the study commenced.

These rats were divided into groups. Some of them received fatty acid-free sunflower oil diets while the rest were supplemented with fish oil. The study result showed that the fish oil group performed better than the fatty acid-deficient group in both reference and working memory.

Furthermore, the results showed that when fish oil was given during early life when the brain was still developing and then continued into adulthood, the enhancement of both types of memory was even more significant.

The researchers found increased levels of DHA in the hippocampus and olfactory bulbs than other parts of the brain.

Furthermore, they also found out that these parts were least likely to lose their DHA store when fatty acid-deficiency diet was resumed and when the diet changed back to include fish oil, those two parts of the brain recovered faster than visual cortex, frontal cortex and cerebellum.

Just like the last study, this study showed that fish oil, and especially the DHA it contains, are essential for learning and memory. The study also provide an indication of the possible sites in the brain where DHA produces its healthful effects.

Possible Benefits for the Old and Alzheimer Patients

In a 2003 study published in the Proceedings of the National Academy of Sciences, researchers investigated the effect of fish oil on the levels of arachidonic acid and docosahexaenoic acid in the brains of aged rats.

The basis for this study lies in the observation that DHA and arachidonic acid levels are reduced in the brains of the elderly and people living with Alzheimer’s disease. Clearly these two fatty acids have a significant contribution to memory and learning.

While some of the 2-year old rats received placebo, the others were fed fish oil containing 27% DHA for 1 month and then gene expression analysis and fatty acid composition of select areas of their brains were determined.

The results showed that of the fatty acids found in the brain, only the levels of DHA was increased. In addition, there were changes in the expression of at least 23 genes in the hippocampus of the rats who fed on fish oil.

Of important note is the tenfold expression of a factor known as transthyretin.

Transthyretin is known to scavenge beta amyloid proteins, the plaque-forming factor in the brains of Alzheimer’s patients.

Therefore, this study demonstrates that fish oil supplementation may be provide some benefits in improving memory and learning in the elderly as well as reversing cognitive decline in Alzheimer patients.

In Humans

Researchers from Massey University in New Zealand recruited 176 healthy adults for their study.

Over a period of 6 months, these volunteers were given supplements containing DHA. When their cognitive functions were tested and compared to the results obtained before the study, clear improvements in memory were observed.

The key factors that improved following DHA supplementation are memory, working memory and speed of working memory. The results showed that, on the average, the male participants of the study demonstrated 15% improvement in working memory while the women showed 7% increase in the speed of episodic memory.

The Case against Fish Oil

A 2008 study published in the journal, Neurology, investigated the effect of fish oil on cognitive performance in the elderly.

This double-blind, placebo-controlled study recruited 302 healthy volunteers who were 65 years or older and still had healthy cognitive functions. They were divided into 3 groups. While one group received placebo, the other groups were given fish oil supplements.

One of the 2 fish oil groups received 1800 mg per day of EPA and DHA while the other group got 400 mg per day of the same supplements. After 26 weeks of supplementation, all 3 groups were tested for attention, motor speed, memory and executive functions.

The result showed that the group who got the higher fish oil dose experienced a 238% increase in plasma concentrations of EPA and DHA, on the average. The lower dose group saw an average increase of 51%.

The cognition tests showed that there was no significant improvement in all cognitive parameters tested in all 3 groups of the patients.

This study concluded that although fish oil supplementation increased the plasma levels of DHA and EPA, it did not improve memory and learning in healthy, old people.

In another study undertaken by the National Institute on Aging, the hypothesis that DHA supplementation can slow the progression of Alzheimer’s disease was tested.

This study, Alzheimer’s Disease Cooperative Study, involved 402 patients with mild to moderate Alzheimer’ disease. Each person in the study group either took a placebo or 2 g of DHA for 18 months.

The results showed that there was no difference between the DHA group and placebo group after 18 months. On the average, the disease progressed at similar rates in both groups and cognitive functions were not improved.

However, the researchers found a curious difference by reinterpreting the data according to a genetic differentiator for Alzheimer’s disease.

What the researchers discovered was that the patients with ApoE-e4 gene variant (linked with an increased risk of Alzheimer’s disease) saw no benefit from DHA supplementation. However, patients who did not have this gene variant still experienced memory decline but at a slower rate than the rest of the study participants.

However, the most damaging result to fish oil’s claim to improving memory was delivered by the Cochrane review of the major, published, large studies done on the subject.

In a review of the 3 largest clinical trials done on patients who were at least 60 years and older, fish oil, DHA or omega-3 fatty acids failed to demonstrate a clear-cut improvement in memory and cognitive function.

This overarching review pooled together results from over 3500 study participants and included studies  as short as 6 months and as long as 40 months.

In Conclusion

Much as the Cochrane review concluded that there omega-3 fatty acids provide no benefit for cognitive health of older people, the authors were quick to note the limitations of the summary.

For one, the authors noted that the studies pooled together for the review only had short follow-up periods, and it may be that omega-3 supplementation takes a long while to produce obvious benefits on memory and learning.

In fact, such suggestions may prove to be right given that some positive studies done with animal models indicate that the longer the supplementation with fish oil, the better the result on memory and cognitive functions.

Secondly, this Cochrane review and most studies that fail to see some benefits to fish oil supplementation involve old adults who already have neurodegenerative diseases such as Alzheimer’s.

In contrast, most studies involving young, health subjects (whether humans or in animal models) report clear improvements in memory functions.

As stated before, long-term supplementation with fish oil is most likely required for significant improvements in memory to show. And where this supplementation proceeds during the formative years, cognitive functions are usually resilient to neurodegeneration.

In conclusion, fish oil should be taken to improve memory.

It should be taken to supplement the primary treatment though. This is because there is a good chance that it is effective especially when taken for long. Where supplementation is unsustainable, dietary sources of omega-3 fatty acids should be adopted.

Even if fish oil does not improve memory, it has been proven to have other health benefits. Therefore, there is more than one good reason to include this oil in your diet.

Sources


http://www.nlm.nih.gov/medlineplus/druginfo/natural/993.html

http://www.sciencedirect.com/science/article/pii/S0306452299001074

http://jn.nutrition.org/content/138/6/1165.short

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