Fish oil DHA doesn't help Alzheimer's disease - What you need to know

Docosahexaenoic acid or simply DHA found in fish oil does not seem to reduce the rate of cognitive and functional decline, which may lead to dementia like Alzheimer's disease, a new trial study suggests.

The study published in the Nov 3, 2010 issue of JAMA did not find an association between taking DHA supplements and slowed progression of Alzheimer's disease in those who were diagnosed with the disease at baseline.

Observational studies have already suggested eating oily fish or taking DHA-rich fish oil or DHA supplements may reduce risk of Alzheimer's disease, but fewer trials offer evidence to prove or disprove the suggestion.

The trial started with 401 people with Alzheimer's disease, a major type of dementia. About 171 patients completed the trial.

In the trial, Joseph F.  Quinn M.D. at Oregon Health and Science University and the Portland VA Medical Center in Portland Oregon and colleagues assigned 2 grams of DHA per day to 171 and a placebo to 124 controls with mild to moderate Alzheimer's disease, whose cognitive and functional abilities were assessed with Alzheimer's Disease Assessment Scale.

The researchers found DHA supplementation for 18 months was not associated with any beneficial effect on the rate of change on Alzheimer's Disease Assessment Scale-cognitive subscale, average change in study subjects 8.27 points versus average change in controls 7.98 points.

Additionally the rate of points change on the Clinical Dementia Rating sum of boxes over 18 months was 2.87 for the DHA group and 2.93 for the placebo group.

Results from a MRI substudy showed DHA treatment had no effect on total brain volume change during 18 months.

"In summary, these results indicate that DHA supplementation is not useful for the population of individuals with mild to moderate Alzheimer disease," the authors wrote.

In response, a health observer suggested the trial results may not be applicable to everyone.  For one thing, the results do not mean that taking DHA supplements before symptoms show up is useless as the current trial was conducted in subjects with Alzheimer's symptoms.

Also the health observer suggested the dose used in the study may not be big enough to have an impact even though the amount may well represent what an average American has from diet or supplements.

In other words, the trial did not prove that using more than 2 grams of DHA per day was useless in slowing the progression of dementia or Alzheimer's disease.

One concern, he pointed out, is that people in the United States eat too much of omega 6 fatty acids which are abundantly present in vegetable oils like soybean oil and corn oil.

Fotuhi M. and colleagues from LifeBridge Health Brain & Spine Institute, Sinai Hospital of Baltimore published a review in the March 2009 issue of Nature Clinical Practice: Neurology saying the ratio of omega-6 to omega-3 fatty acids is important in maintaining neurological functions.

They wrote "the existing data favor a role for long-chain omega-3 fatty acids in slowing cognitive decline in elderly individuals without dementia, but not for the prevention or treatment of dementia including AD."

The authors came to the conclusion after reviewing 11 observational studies and four clinical trials.  Three observational studies showed intake of long chain omega-3 fatty acids reduced cognitive decline and four of eight remaining observational studies linked  omega -3 fatty acids with reduced risk of Alzheimer's disease or dementia.

None of the four clinical trials found evidence that omega-3 fatty acids prevent or treat any form of dementia.

They said "This apparent dichotomy might reflect differences in study designs with regard to participants, dosages, the ratio of long-chain omega-3 to omega-6 fatty acids, or the choice of outcome measurements."

David Liu