If a daily fish oil capsule is part of your plan for keeping your memory sharp into old age, a two-year clinical trial from the University of Southern California offers a sobering result. The supplement did reach the brain. It did not improve memory, and it did not slow the shrinking of the brain region that memory depends on.
Fish oil is big business. Americans spend more than $1 billion a year on these supplements, much of it in the hope of protecting the brain. The reasoning is not far-fetched: omega-3 fatty acids are building blocks of brain cells and help nerve cells communicate, and people who eat little fish or have low omega-3 levels have been linked in earlier research to a higher risk of dementia. A link of that kind, though, never showed that a pill could change the outcome.
The new trial, led by Dr Hussein Naji Yassine, director of the USC Center for Personalized Brain Health at the Keck School of Medicine of USC, was published this year in the peer-reviewed journal eBioMedicine. Its 365 volunteers, aged between 55 and 80, seldom ate fish, were thinking normally when they joined, and each had one or more known risk factors for Alzheimer's disease. About 47% carried APOE4, the strongest known genetic risk factor for the late-onset form of the disease.
What did volunteers actually take? Half were given 2,000 mg a day of docosahexaenoic acid (DHA), one of the main omega-3s in fish oil, and half took a placebo. Neither the volunteers nor the researchers knew who was getting which. The dose is at least twice what most large earlier omega-3 trials used.
Six months in, the signs were encouraging. Samples of cerebrospinal fluid showed DHA levels up by an average of 17%, evidence that the fatty acid had crossed from the blood into the central nervous system.
By the two-year mark the picture had changed. People on DHA scored no better than the placebo group on memory and thinking tests, and brain scans showed no slowing in the shrinkage of the hippocampus, the memory hub that doctors track as a marker of brain ageing and Alzheimer's risk. APOE4 carriers saw no extra benefit either. "Our results do not support fish oil supplements as a preventive measure against Alzheimer's," Yassine said.
Does this mean omega-3s are useless for the brain? The researchers do not say that. Yassine's view is that a supplement on its own is not enough, and his team suspects omega-3s may do more as part of a wider eating pattern such as the Mediterranean diet, an idea this trial did not test. Other specialists point out that everyone started out mentally healthy and that the placebo group itself showed little decline over two years, which makes any protective effect hard to detect in that time. The findings also apply to this dose and this age group.
Dr Pieter Cohen, an associate professor at Harvard Medical School who was not involved, said the trial adds to the evidence that omega-3 supplements have no proven benefit for treating or preventing dementia. Yassine points instead to regular exercise, good sleep and a balanced diet rich in fibre, calling a healthy lifestyle the most powerful tool available for lowering Alzheimer's risk.
His team is now studying the proteins that break down omega-3s in the body. In January it reported candidate drugs that block one of them, so far tested only in cells and mice.
