It is one of the most-popular dietary supplements in the U.S., with many people taking fish oil or some form of Omega 3 supplement based on claims it helps the heart and brain. But the opposite could be true. For at least for one component, it could actually impede efforts by the brain to heal itself after injury, according to a new study from Medical University of South Carolina.
It joins other recent studies that seriously question whether fish oil is beneficial for health. Some show it may actually do more harm than good.
Fish oil supplements or similar ones that offer Omega 3 fatty acids are part of the daily routine for millions of people. A survey in 2025 of adults who take supplements found that nearly half include it in their regimen, making it the third-most popular. Another study estimated that one in five adults age 60 and older take fish oil in the belief that it helps their heart, their brain or has general health benefits. Makers of the supplements frequently make these claims, often without evidence.
The supplements take advantage of longstanding evidence that eating fish high in Omega 3 fatty acids has been shown to lead to lower risk of heart disease. This includes a wide variety of fish, including anchovies, salmon and tuna. The reasoning goes that taking supplements with some of those same Omega 3 elements would confer the same benefit. Many supplements expand that beyond the heart to include brain health and easing joint pain, among others.
But those claims are coming under increasing scrutiny. The MUSC study focused on the brain health claim. Of the Omega 3 fatty acids in supplements, the two most common are abbreviated EPA and DHA. These are not fats or lipids that the body can produce and must be added by diet, said Dr. Onder Albayram, corresponding author on the new study published in the journal Cell Reports.
“You have to eat it,” he said. Omega 3 fatty acids have been almost universally promoted as being neuroprotective or helping to protect the brain, said Albayram, an associate professor in the Department of Pathology and Laboratory Medicine and the Department of Neuroscience.
Consuming those fatty acids regularly over a period of time may cause them to accumulate in different areas of the body. That is what Albayram and colleagues found when they used a mouse model to study it. The brain normally doesn’t metabolize those fatty acids, so the stores tend to sit there.
When researchers introduced regular mild traumatic brain injuries to the mice, similar to concussions, the stores of EPA fatty acids were mobilized during the subsequent effort to repair the brain. Instead of helping, however, it seemed to interfere with the formation of new blood vessels that are necessary to carry oxygen and nutrition into the damaged areas, Albayram said. It also appeared to interfere with the normal function of the cells that line blood vessels and resulted in a malformed structure. That appeared to lead to cognitive decline.
The resulting disease appeared to be similar to chronic traumatic encephalopathy, or CTE, which is a major problem in former football players and others who have suffered repetitive head trauma. Colleagues on the study from the Boston University Alzheimer’s and CTE Center, which houses human brains donated by former NFL players, were able to provide those brain samples and the results were strikingly similar Albayram said.
While there may be other health benefits from Omega 3 fatty acids, the study “shows very clearly that nutritional strategies for brain health may need to become more precise and context aware,” Albayram said.
It is only the latest study to point out the shortcomings of Omega 3 supplements. While acknowledging the potential benefits of those fatty acids in reducing the risk of some heart disease, some cardiologists warn that they must be balanced by a potential increased risk in other serious heart conditions, such as atrial fibrillation or a rapid and irregular heartbeat.
A British Medical Journal study found that the benefit and harm of regular fish oil use were based entirely on context: among people with heart disease, the supplements decreased the risk of progressing to worse conditions. Among health people, regular doses of the supplements increased the risk of atrial fibrillation and slightly increased the risk of stroke.
The bottom line is whether the supplements are helpful or harmful is based on the context of why someone is taking them and for what benefit, Albayram said.
“The biology may be more nuanced than what we thought,” he said.