The old wives used to claim that fish is brain food. Little by little, scientists are catching up to this idea. The popularity of fish oil has varied over the years, but several studies suggest benefit.
Does Fish Oil Protect People from Dementia?
A recent study suggests that some older people are less prone to Alzheimer disease if they take fish oil capsules (JAMA Network Open, Aug. 1, 2024). This may be the easiest way to get a specific amount of fat from fish.
Scientists at Oregon Health & Science University conducted the clinical trial with 102 volunteers who were at least 75 years old. MRIs of the participants’ brains at the start and again at the finish of the three year study showed fewer white matter lesions in those taking fish oil instead of soybean oil, but only for certain individuals. Those with the gene for APOE4 that predisposes people to Alzheimer disease got significant benefit from the fish oil supplements. Others without elevated risk did not have a significant improvement.
People with Higher Levels of Omega-3 Fats Perform Better on Tests:
Investigators at the University of Texas measured blood levels of fat from fish (omega-3 fatty acids) in the blood of more than 2,000 volunteers (Neurology, Oct. 5, 2022). The middle-aged participants took tests to determine their cognitive capacity. As volunteers for the Framingham Heart Study, they also submitted to brain scans that measured brain volume.
Omega-3 fatty acids (EPA and DHA) are abundant in cold-water fish such as anchovies, sardines, salmon, trout and tuna. People with higher levels of omega-3 fats in their blood performed better on cognitive tests and had larger hippocampal regions. This area of the brain is associated with memory.
In an earlier study, California scientists found that higher levels of DHA appear helpful for older individuals as well.
What Is the Relationship Between Fat from Fish and Brain Health?
The researchers recruited volunteers from the Aging Brain Study and analyzed their serum levels of docosahexaenoic acid, abbreviated DHA (JAMA Neurology, October 2016). Like eicosapentaenoic acid (EPA), this is a fat from fish.
The 61 study participants also underwent brain imaging to detect amyloid plaques, linked to Alzheimer disease. People with higher blood levels of DHA had lower amounts of amyloid plaque in their brains.
In addition, those with higher DHA levels had better scores on a test of nonverbal memory. Areas of their brains usually damaged by Alzheimer were larger and presumably healthier. Alzheimer disease is frequently associated with brain shrinkage.
The authors warn that
“limited seafood intake may increase the risk of brain amyloid deposition and Alzheimer disease.”
A few previous studies have found a connection between a diet rich in fish or seafood and a reduced risk of dementia or cognitive decline. We wrote about a meta-analysis of 21 studies here. Unfortunately, previous studies suggest that taking fish oil or DHA in a supplement may not be able to prevent or reverse Alzheimer disease. (You can read about those studies here and here.)
Fat from Fish May Protect Brains from Degeneration:
Another recent study considered how often older people in coastal Ecuador consumed oily fish (European Stroke Journal, Sep. 2022). Participants in the Atahualpa Project Cohort, all at least 60 years old, agreed to MRI imaging of their brains. They also answered detailed questionnaires about their diets, with particular emphasis on fish rich in omega-3 fats. After more than six years, those who ate the most fat from fish had the least MRI evidence of damaged white matter in their brains.
Downsides of DHA:
One downside of taking fish oil supplements is a higher risk of atrial fibrillation, a heart rhythm disturbance.
In addition, some studies suggest that men taking DHA supplements may be more likely to develop aggressive prostate cancer. (We wrote about another study of DHA and prostate cancer here.) While most studies suggest that eating fish or seafood is beneficial for the heart or the joints, it is not clear whether eating more fish might put men at higher risk of this potentially deadly cancer.
