Omega-3 fatty acid supplements may slow cognitive decline in some patients with very mild Alzheimer's disease, but do not appear to affect those with more advanced cases, according to results of a clinical trial.
Alzheimer's disease is a severely debilitating condition that affects thinking, learning and memory, beginning with declines in episodic memory (including memory about events in one's own life), according to background information in the article. Medications are available to treat the symptoms, but these drugs do not affect the underlying cause and progression of the disease. Several studies have shown that eating fish, which is high in omega-3 fatty acids, may protect against Alzheimer's disease, leading researchers to question whether supplements could have similar effects.
Yvonne Freund-Levi, M.D., Karolinska Institutet, Stockholm, Sweden, and colleagues compared the effects of supplements containing two omega-3 fatty acids with placebo in 204 patients with Alzheimer's disease, 174 of whom completed the entire study. For six months, 89 patients (51 women and 38 men) took 1.7 grams of docosahexaenoic acid (DHA) and .6 grams of eicosapentaenoic acid (EPA), while 85 patients (39 women and 46 men) took placebo. For an additional six months, both groups took the omega-3 fatty acids. Patients had physical examinations, which included blood tests and blood pressure measurement, and took cognitive tests at the beginning of the study and at the six- and 12-month marks.
After six months, there was no difference in the rate of cognitive decline between the two groups. However, among a subgroup of 32 patients with very mild cognitive impairment at the beginning of the study, those who took the fatty acids experienced less decline in six months compared with those who took placebo. Among those who took placebo during the first six months, decline decreased during the second six months, when they also began taking the omega-3 supplements. The supplements appeared safe and well-tolerated, with no change in blood pressure or blood test results other than a higher ratio of fatty acids in the blood.
"The mechanisms by which omega-3 fatty acids could interfere in Alzheimer's disease pathophysiologic features are not clear, but since anti-inflammatory effects are an important part of the profile of fish oils, they are conceivable also for Alzheimer's disease," the authors write. This could potentially explain why effects were seen only in those with very early-stage disease—recent evidence suggests that there is a critical period two or more years before patients develop dementia when levels of chemicals that signal the presence of inflammation are elevated. "It is possible that when the disease is clinically apparent, the neuropathologic involvement is too advanced to be substantially attenuated by anti-inflammatory treatment."
The authors also point out that "these findings cannot serve as a basis for general recommendations for treatment of Alzheimer's disease with dietary DHA-rich fish oil preparations. However, studies in larger cohorts with mild cognitive impairment, including those at risk for Alzheimer's disease, are needed to further explore the possibility that omega-3 fatty acids might be beneficial in halting initial progression of the disease."