The surprising findings come from an 18-month, placebo-controlled clinical trial that enrolled 402 people with mild-to-moderate Alzheimer's disease at 51 clinical centers.
Previous studies have shown that people who eat lots of fish have a significantly lower risk of Alzheimer's disease, and significantly lower levels of amyloid, the chief component of the plaque that clogs patients' brains.
To investigate, researchers studied almost 400 men and women with an average age of 76 with mild to moderate Alzheimer's. Participants were randomly assigned to take either 200mg DHA pills, a type of omega 3 fatty acid, or placebo pills daily for 18 months.
DHA occurs naturally in the brain but is found in reduced amounts in people with Alzheimer's disease.
The trial found similar rates of physical and mental decline in both groups using scoring systems and MRI brain scans.
Supplements did not slow the development of Alzheimer's even in a subgroup of patients with the mildest symptoms.
Researchers note in The Journal of the American Medical Association that based on these findings there is no basis for recommending DHA supplementation for patients with Alzheimer's disease.
Supporters of fish oil's benefits pointed out that the latest study did not investigate whether supplements could ward off the onset of Alzheimer's in the first place.
According to the Alzheimer Society of Canada, half a million Canadians have Alzheimer's disease or a related dementia. This means that 1 in 11 Canadians over the age of 65 currently has Alzheimer's disease or a related dementia.
Warning signs of the disease include memory loss, disorientation of time and place, poor or decreased judgment, changes in mood and misplacing things.
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