Fish oil reached the brain but didn't protect it, trial finds

Americans spend more than $1 billion a year on fish oil supplements, and for many the reason is the brain: they take omega-3s hoping to hold on to their memory as they age. A rigorous new trial from the University of Southern California, published in the journal eBioMedicine, tested that hope head-on, and the capsules fell short.

No large-scale prevention trial had tested high-dose omega-3s this way in older people who were not yet showing dementia. The study also did something unusual: it checked whether the supplement was actually getting into the brain, not just whether people scored better on a memory test.

A stricter kind of test

This was not a survey of what people happened to eat. It was a randomized, double-blind, placebo-controlled trial, the strongest design for working out whether a treatment does anything. Researchers followed 365 adults between the ages of 55 and 80. Each had at least one dementia risk factor and a low dietary DHA intake, the main omega-3 in oily fish, so there was room for a supplement to help. Half were assigned 2,000 mg of DHA a day and half a placebo, taken for two years.

The omega-3 got in. The brain stayed the same.

Did two years of high-dose fish oil protect these brains? No. After six months, omega-3 levels in the fluid around the brain and spinal cord had climbed in the fish oil group but not the placebo group, showing the supplement was reaching the brain. Yet across the two years, the fish oil and placebo groups showed no differences in brain volumes or in tests of memory and thinking. The omega-3 got in. It simply did not help.

Omega-3s do help build the connections between brain cells, but the trial’s lead investigator, Hussein Yassine, said the results “do not support fish oil supplements as a preventive measure against Alzheimer’s”.

The trial had real limits. Dropout was high, at 38 percent, mainly due to COVID, which the authors noted. On safety there was better news: no serious adverse events were attributed to the treatment, so the high dose itself looked well tolerated.

Fish on the plate, not oil in a capsule

None of this makes omega-3s worthless. Reviews of the wider research suggest omega-3s may have a protective effect against cognitive decline in healthy people, though the trial results have been inconsistent. And one thread runs through the guidance from health agencies: for some health conditions, the evidence for benefits from eating fish is stronger than the evidence for omega-3 supplements. A capsule is not a plate of salmon or sardines, and eating patterns that feature fish, like the Mediterranean diet, are the ones most often tied to healthier brain aging.

Why the supplement did not help is still an open question. The team is now studying how the brain processes omega-3s, and whether things like poor health, diet, genetic risk and age change the brain’s ability to absorb and use them.

What it means for your fish oil habit

So what should you do with the bottle in the cupboard? People take fish oil for several reasons, and this study trained on just one of them: protecting the aging brain. For that goal, in these at-risk older adults, a high dose did nothing a placebo did not. Anyone taking omega-3s for their heart or another reason should not change course over a single study, and should check with a doctor first.

The study’s lead investigator was blunt: his team found that fish oil supplements “do not appear to protect brain health”. His real message pointed past the supplement aisle. The most powerful tool for reducing Alzheimer’s risk, he said, is staying healthy for life through regular exercise, quality sleep and a balanced diet.