Key Takeaway:
- High-dose DHA showed no significant benefits: Taking 2,000 milligrams daily for two years did not improve memory or protect brain structure.
- Higher DHA levels didn’t improve outcomes: Increased DHA levels in cerebrospinal fluid did not translate into measurable cognitive benefits.
- Fish oil isn’t a proven Alzheimer’s preventive: The findings challenge supplement-based prevention claims but do not rule out benefits from dietary omega-3s.
A two-year clinical trial of 365 older adults found that high-dose docosahexaenoic acid (DHA), an omega-3 fatty acid, did not significantly improve memory or protect against brain shrinkage, challenging its use for Alzheimer’s prevention.
Researchers test high-dose DHA in older adults
Researchers at the University of Southern California’s Keck School of Medicine studied 365 adults ages 55 to 80 who rarely ate fish and faced an elevated risk of Alzheimer’s disease. The randomized, double-blind trial compared participants taking 2,000 milligrams of DHA daily with those receiving a placebo.
Published in eBioMedicine, the study examined whether increasing DHA levels in the brain could improve cognitive performance or protect brain structure over 24 months. DHA is an omega-3 fatty acid that plays an important role in brain cell membranes and supports normal nerve cell function.
Researchers measured DHA levels in cerebrospinal fluid, which surrounds the brain and spinal cord, to determine whether the supplement reached the central nervous system. After six months, DHA levels had increased by 17% among participants receiving the supplement.
However, the increase did not translate into measurable improvements in memory or other cognitive abilities. Brain imaging also showed no significant difference in brain volume between the DHA and placebo groups over the study period.
Higher DHA levels do not protect memory
The findings suggest that delivering more DHA to the brain does not necessarily improve its performance or prevent structural changes associated with aging. The hippocampus, a brain region important for memory formation, showed no significant protection against shrinkage among participants taking the supplement.
Hussein Naji Yassine, the study’s lead investigator and director of USC’s Center for Personalized Brain Health, said the findings challenge the idea that fish oil supplements can prevent Alzheimer’s disease.
“We all wish there was a silver bullet for preventing Alzheimer’s, but our findings showed that fish oil supplements do not appear to protect brain health,” Yassine said in a statement released by USC.
Nearly half of the study participants carried the APOE4 gene variant, a known risk factor for late-onset Alzheimer’s disease. However, the researchers found no significant cognitive or brain-structure benefits from DHA supplementation over the trial.
The study also reported comparable adverse events between the two groups, with no serious adverse events attributed to the treatment. Researchers noted that 38% of participants dropped out, mainly because of the COVID-19 pandemic, which is an important limitation when interpreting the results.
Researchers call for a broader approach to brain health
The results do not establish that omega-3 fatty acids are ineffective in every context or that eating fish provides no health benefits. Instead, they indicate that high-dose DHA supplements alone did not improve the measured outcomes in this particular group of older adults.
The researchers are investigating whether age, genetic risk, overall health, and dietary patterns influence how the brain processes omega-3 fatty acids. A Mediterranean-style diet, which includes fish, vegetables, fruits, whole grains, legumes, nuts and olive oil, provides a broader combination of nutrients, although this trial did not directly compare that diet with supplementation.
The study authors said future research should focus on how the brain metabolizes DHA rather than simply testing higher supplement doses. The findings underscore the difference between a nutrient reaching the brain and producing a measurable health benefit.
Researchers continue to emphasize healthy aging practices, including regular physical activity, adequate sleep, and a balanced diet, as part of a broader approach to brain health. People taking prescribed supplements should consult their health care professionals before changing their regimen.
