Study on DHA Supplements and Brain Health
Docosahexaenoic acid (DHA), an omega-3 fatty acid present in oily fish like mackerel and sardines, is widely believed to enhance cognitive function by strengthening connections among brain cells. Yet, definitive proof that DHA supplements truly reach the brain or provide tangible benefits against dementia has been lacking.
In this context, researchers from the USC School of Medicine recently published findings from an extensive two-year clinical trial involving older adults who were at a higher risk for developing Alzheimer’s disease. The study indicated that while high-dose DHA supplements do make their way to the brain, they do not seem to improve memory or cognitive abilities, nor do they slow down brain atrophy.
“Everyone hopes for a silver bullet to prevent Alzheimer’s disease, but we can’t say that fish oil supplements protect brain health,” said Hussein Naji Yassine, who leads the Personalized Brain Health Center at USC. “While omega-3s play an important role in forming brain cell connections needed for cognition, our findings do not support fish oil supplements as an effective preventive measure against Alzheimer’s.”
DHA Reached the Brain, But …
Yassine and his team carried out a randomized, double-blind, placebo-controlled study with 365 participants aged 55 to 80 who didn’t frequently consume fish. Notably, almost half of the participants (47 percent) carried the APOE ε4 allele, which is linked to a higher genetic risk for late-onset Alzheimer’s. All participants ingested less than 200 mg of DHA daily through their diets.
The participants were divided into two groups. One group took a daily supplement consisting of 2,000 mg of DHA, while the other received a placebo for a duration of 24 months. The placebo, made of corn and soybean oil, looked, tasted, and smelled just like the DHA supplement. Neither the participants nor the researchers were aware of who received which treatment.
The initial goal was to confirm whether DHA actually reached the brain. Measurements of DHA levels in the cerebrospinal fluid surrounding the brain and spinal cord showed a 17 percent increase after six months in the DHA group. Interestingly, there was no difference observed between carriers and noncarriers of the APOE ε4 allele, providing clear evidence that high-dose DHA supplementation reaches the brains of cognitively healthy older adults irrespective of APOE ε4 status.
However, the results concerning cognitive function and brain structure were quite different. After 24 months, participants completed a standardized test for memory and cognitive performance, the Repeatable Battery for the Assessment of Neuropsychological Status. The findings revealed no significant differences between the DHA and placebo groups. Moreover, there were no notable changes in the volume of the hippocampus, a crucial brain area for memory and an early marker of Alzheimer’s disease.
Why Didn’t It Work?
The researchers put forth various reasons for why DHA reached the brain but didn’t yield measurable clinical advantages. One possibility is the action of an enzyme that interferes with DHA metabolism in the brain. An enzyme known as calcium-dependent phospholipase A2 (cPLA2), when activated, may break down DHA before it can be utilized in synaptic membranes—the areas where DHA likely plays its most vital role in cognitive support.
Another reason could be that many participants had cardiovascular issues such as obesity, hypertension, or a sedentary lifestyle. The chronic inflammation that accompanies these health conditions might have tempered the effects of supplementation, making it challenging for a single nutrient to deliver significant benefits.
Additionally, the participants were relatively young, averaging 66 years old, and experienced only minimal cognitive decline over the two-year span. Consequently, there may not have been enough decline during the trial to identify any protective impact from DHA supplementation.
