The results of a two-year clinical study have cast doubt on the effectiveness of omega-3 fatty acid supplements for preventing dementia and Alzheimer’s disease. Taking fish oil capsules did not show any positive impact on brain health among the study participants.

Omega-3 fatty acids are considered important for overall health, especially for the central nervous system. Docosahexaenoic acid (DHA), a type of omega-3, plays a crucial role in brain function as a structural component of neuronal membranes, supporting synaptic connections and reducing inflammation. Omega-3s are not synthesized in the human body and must be obtained from food, primarily from fatty sea fish. Fish oil supplements are widely used because they are believed to benefit the brain and may protect against pathological changes that lead to dementia and Alzheimer’s disease.

However, a recent study conducted in the United States did not confirm the effectiveness of fish oil supplements in preventing these conditions. In a double-blind, placebo-controlled trial lasting two years, researchers found that although omega-3 fatty acids successfully entered the brain, they did not improve brain health indicators in older adults at increased risk for Alzheimer’s disease. High doses of supplements did not enhance memory, cognitive functions, or slow down the loss of brain cells in regions associated with Alzheimer’s.

The study involved 365 men and women aged 55 to 80 who rarely ate seafood. Nearly half of the participants (47%) carried the APOE4 gene, which is considered one of the main genetic risk factors for developing Alzheimer’s disease. In carriers of this gene, DHA is absorbed less efficiently, and its levels in blood and cerebrospinal fluid are typically lower.

Participants were randomly divided into two groups: one received a daily fish oil supplement (2000 mg of DHA), while the other received a placebo. Neither the participants nor the researchers knew who was receiving the supplement and who was getting the placebo. Six months after the study began, DHA levels in the cerebrospinal fluid were measured and found to have increased by an average of 17%. Despite this, cognitive performance did not improve.

Memory and thinking abilities were assessed at the start and after two years. The results of cognitive tests in those taking fish oil supplements did not differ from those in the placebo group. Neuroimaging also did not show any slowing in the reduction of hippocampal volume—a brain region critical for memory and often used as a marker of brain aging and Alzheimer’s risk.

The researchers suggested that these results may be related to differences in how the brain absorbs and uses omega-3 fatty acids from supplements compared to those obtained from food.