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Fish Oil and Alzheimer’s Disease

Clive Liu

2008.10.23

 

Introduction

In the modern world of aging people with longer life expectancies many diseases of age have increased in incidence and prevalence. Among the many diseases that researchers and doctors are attempting to prevent is dementia, which is commonly found as Alzheimer’s disease in older people. According to the Alzheimer’s Disease Fact Sheet by the National Institute on Aging “as many as 4.5 million Americans suffer from Alzheimer’s disease” (http://www.nia.nih.gov/Alzheimers/Publications/adfact.htm). Interestingly, as can be seen on the Alzheimer’s Association’s overview page, this disease “is not a normal part of aging” (http://www.alz.org/alzheimers_disease_alzheimers_disease.asp). As Alzheimer’s disease is degenerative and nothing can cure it, emphasis has been put on postponing or to preventing its course.

Many pharmaceutical and supplemental treatments have been marketed and proposed. On the more traditional side of treatments, which can be found on the Alzheimer’s Association’s Standard Treatments page, are drugs that deal with the brain’s chemical activity, including cholinesterase inhibitors, which “prevent the breakdown of acetylcholine”, and memantine, which “works by regulating the activity of glutamate” (http://www.alz.org/alzheimers_disease_standard_prescriptions.asp#2). Alzheimer’s Association also has an alternative treatments page detailing many such treatments involving supplements such as ginkgo biloba, which is said to have “antioxidant and anti-inflammatory properties” (http://www.alz.org/alzheimers_disease_alternative_treatments.asp#Ginkgo_biloba).  Another of such alternative methods of prevention and treatment involves omega-3 fatty acids, which can be obtained via fish oil.

 

What is fish oil?

Fish oil contains omega-3 fatty acids of eicosapentaenoic acid (EPA) and docosahexanenoic acid (DHA). Omega-3 fatty acids are a type of unsaturated fatty acids that have a double carbon-carbon bond three carbons away from the omega end of the molecule. While nutritionally important for humans, omega-3 fatty acids cannot be synthesized by humans and must be converted from larger fatty acids or ingested from food sources. EPA is important because it is a precursor to clotting factors and many signaling molecules that tells cells where they are and what they are coming in contact with in the human body. DHA is highly concentrated in the brain and eye.

Figure 1. DHA molecule

 

http://upload.wikimedia.org/wikipedia/commons/3/3d/DHAnumbering.png

Figure 2. EPA molecule

 

http://upload.wikimedia.org/wikipedia/commons/0/02/EPAnumbering.png

Claims relating fish oil and Alzheimer’s disease

Figure 3. Salmon Oil Plus Nutrition Facts - http://www.omega-3.us/salmonplus-label.jpg

 

Figure 4. Salmon Oil Plus bottle

http://www.omega-3.us/salmon.jpg

 

According to one retailer of omega-3 supplements, Salmon Oil Plus, omega-3 oils “can help prevent heart disease, maintain optimum blood pressure and cholesterol levels and give almost immediate relief from joint pain, migraines, depression, autoimmune diseases and many other conditions” (http://www.omega-3.us/). And on their tips page, they recommend that the fish oil to be balanced in EPA and DHA, be clean and non-toxic, and from natural sources (http://www.omega-3.us/omega-3/). On a less capitalistic point, the Mayo Clinic site on omega-3 fatty acids, fish oil, alpha-linolenic acid compiles a list of diseases and how omega-3 fatty acids affects said disease. And on the issue of dementia the Mayo Clinic list rated the ability of fish oil to attenuate dementia as a C, or unclear scientific evidence against this use (http://www.mayoclinic.com/health/fish-oil/NS_patient-fishoil). This claim is backed up by Medline Plus, which is another established resource that is used by the public and researchers alike (http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-fishoil.html).

 

Some current research

            To see if such claims on dementia are true, let’s look at some research published recently in medical journals. The InCHIANTI Study found out that “older persons with dementia have lower concentration of n-3 FA” (Cherubini, A., Andres-Lacueva, C., et al., 2007). This result signifies that memory loss is associated with less omega-3s in the blood stream. And one of the proposed future studies the InCHIANTI Study suggested would be to test omega-3 supplements.

            The Framingham Heart Study titled “Plasma Phosphatidylcholine Docosahexaenoic Acid Content and Risk of Dementia and Alzheimer Disease” done by Schaefer, E. J., MD; Bongard, V., MD, PhD; et al. showed that people in the study with higher levels of PC DHA had “a significant 47% lower risk of dementia” (Schaefer, E. J., MD; Bongard, V., MD, PhD; et al., 2006, p. 1550). They also found that “a 50% reduction in the risk of Alzheimer disease was associated with the consumption of more than 2 servings of fish per week” (p. 1550). This study was a prospective study that lasted nine years with a large sample size of 889 men and women. However there was only one time when PC DHA was measured and diet data was selected in a nonrandomized fashion.

In another study, this one done by Nurk, Drevon, et al. titled the “Cognitive performance among the elderly and dietary fish intake: the Hordaland Health Study” found that “intake of fish and fish products is associated with better performance across several cognitive abilities and that the associations are strongly dose-dependent” (Nurk, Drevon, et al., 2007, 1478). This study was cross sectional and drew from a pool of 2031 subjects ages from 70 to 74. They used many tests including the Kendrick Object Learning Test, Trail Making Test (part A), modified versions of the Digit Symbol Test, Block Design, Mini-Mental State Examination, and Controlled Oral Word Association Test. These results indicated that subjects who had more fish in their diet did better on the cognitive tests and that the most fish equated to better scores.

In a more interesting study and a more recent article by van de Rest, et al titled “Effect of fish oil on cognitive performance in older subjects” was a “double-blind, placebo-controlled trial involving 302 cognitively healthy…individuals aged 65 years or older” (van de Rest, et al 2008, p. 430). This clinical trial set up is pretty much the gold standard so its results should be pretty good. Using two different quantities of EPA and DHA, 1,800 mg/d EPA–DHA and 400 mg/d EPA–DHA, and a placebo people were told to take the supplements for 26 weeks. At the end of that time, people’s blood was drawn to see if they were actually taking the supplements. Results of a rise in EPA and DHA levels, 238% in the high-dose and 51% in the low-dose, in blood indicated that indeed they were taking the supplements. Thus conclusions could be drawn due to the fact that there was an actual independent factor being changed, in this case EPA and DHA levels. Using cognitive tests and the baseline tests from earlier, van de Rest, et al found that there was no significant difference between the two doses or the placebo. These results indicate that EPA and DHA had no effect on cognitive performance.

 

Conclusions about fish oil

            Considering some of the research published in the scientific journals, we can see that there is a mix of results for whether fish oil is good at attenuating the effects of dementia and thus Alzheimer’s disease. It seems that the less well designed studies tended to show significant improvements in cognitive abilities. Whereas the gold standard double-blind, placebo-controlled trial showed that there were no significant differences in adding fish oil supplements into one’s life. However as long as the supplement is of a reputable source, without toxins and such, there seems to be no harm from adding it to one’s diet, especially for those over the age of 65.

             

 

References

Cherubini, A., Andres-Lacueva, C., et al. (2007). Low Plasma N-3 Fatty Acids and Dementia in Older Persons: The InCHIANTI Study. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 62,1120-1126.

Nurk, E., Drevon C. A., et al. (2007). Cognitive performance among the elderly and dietary fish intake: the Hordaland Health Study. American Journal of Clinical Nutrition, Vol. 86, No. 5, 1470-1478.

Schaefer, E. J., MD; Bongard, V., MD, PhD; et al. (2006). Plasma Phosphatidylcholine Docosahexaenoic Acid Content and Risk of Dementia and Alzheimer Disease: The Framingham Heart Study. Archives of Neurology, 63:1545-1550.

van de Rest, O., MSc, Geleijnse, J. M., PhD, et al. (2008). Effect of fish oil on cognitive performance in older subjects. Neurology, 71, 430-438.

 

 

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