Another promising dietary supplement fails to deliver protection against a target disease, this time Alzheimer’s. Image courtesy of outcast104.

Another promising dietary supplement fails to deliver protection against a target disease, this time Alzheimer’s.

DHA (or docosahexaenoic acid for the geekier among you) is an omega-3 fatty acid that is abundant in the brain. Epidemiological studies have suggested that people who consume more DHA from fish have a lower incidence of Alzheimer’s disease. Further, DHA supplementation has improved markers of cognitive impairment in mouse models of Alzheimer’s disease.

Scientists speculated that DHA supplementation may be beneficial in treating cognitive decline because previous research has suggested that among all omega-3 fatty acids, DHA was the only one associated with a reduced incidence of impairment. Also, the other major omega-3 fatty acid found in fish, eicosapentaenoic acid (EPA), is not present in the human brain, whereas DHA is abundant.

The study, published in JAMA, was a collaborative effort by scientists from the Oregon Health and Science University, UC San Diego, Yale, UC San Francisco, NYU and others. It was a randomized, double-blind, placebo-controlled trial of DHA supplementation in patients with mild to moderate Alzheimer’s disease.

The researchers found no benefit of 2 g/day DHA supplementation on cognitive performance on the Alzheimer’s Disease Assessment Scale (ADAS) or Clinical Dementia Rating (CDR) compared to placebo. There was also no measurable benefit of DHA on brain volume, which typically declines with Alzheimer’s progression.

Though this research does not rule out a benefit of DHA on cognitive health, it does not bode well for regular supplementation. The treatment lasted for 18 months and cognitive changes were detected in both groups. So if DHA had any effect on the rate of cognitive decline it should have been apparent.

It is possible that beginning DHA treatment after early signs of Alzheimer’s have already been detected is too late for any meaningful protection offered by DHA. Maybe some benefit would have been found if the treatment began in healthy adults before symptoms of cognitive decline developed.

It may also be that DHA is beneficial, but is not effective in supplement form. DHA is very vulnerable to oxidative damage, and some research has shown that it provides more cognitive benefit when co-administered with an antioxidant (lutein) to protect it. DHA ingested in the form of food (fish) would not be subject to the same level of oxidative degradation, which may explain the results seen in epidemiological data.

It is not uncommon for supplements to fail to replicate epidemiological benefits seem from foods, and more careful studies are needed to determine the nutritional benefit, if any, of DHA on cognitive aging.

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D'OH! DHA Supplements Don't Reduce Alzheimer's Risks 10 December,2010Darya Pino

  • GOED Omega-3

    Agreed that it is unfortunate that the study did not find a benefit, but your article is mixing two very different issues, prevention and treatment. The JAMA study found that short-term DHA did not reverse the damage of Alzheimer’s in patients who already had progressed quite far, the epidemiological evidence you cite is much longer term and is on the role of DHA helping prevent the onset of Alzheimer’s. No intervention study has been done yet to replicate the preventive effects seen in the epidemiological studies, but there was one just recently published that came close, the MIDAS study. This study looked at the effects of slowing down cognitive decline in patients with very early stage dementia (pre-Alzheimer’s). The effects were positive, which also may show how reducing the risk of a disease and treating it after you have it are very different things, particularly with Alzheimer’s. More studies are needed into this area to determine the true role of DHA, if any, in Alzheimer’s progression.

  • Anonymous

    This was very reasonable to me because to fish intake and current omega 3 fatty acids intake are very different for me.I discovered new method to extract fish oil, which not easy oxidation because its contains natural vitamins specially, abundant E and D.
    This method is on line Nature Precedings,
    and was patented in Japan.
    As there are many studies for Alzheimer Disease and DHA, Vitamin E and D I expected this my oil is useful for improvement of Alzheimer disease.
    The Father of my friend had Alzheimer disease in advanced stage, so I recommended my oil in capsules ,9 capsules per days 2.7g of pure undenatured tuna oil and less than one month he started take coffee alone and he could wait his wife from shopping, recognize her when she’s back and stay his house alone which was impossible before.
    I think this oil contains all natural functional components of tuna improves Alzheimer disease as fish intake improved it.
    I’m worrying for the quality of raw material used for fish supplement and extraction method to change form of fish oil triglyceride to mono or diglyceride or produce trans fatty acids.
    More than 90% of current DHA supplement use raw material which the NASA developed safety food processing system HACCP.


Darya Pino

Darya Pino is a Ph.D trained scientist, San Francisco foodie, food and health writer and advocate of local, seasonal foods. She shares her unique scientific perspective on health and enthusiasm for delicious foods at her website Summer Tomato. Follow her on Twitter @summertomato.

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