Millions of Americans take fish oil supplements in hopes of protecting their memory and keeping their brains healthy as they age. These products have become a major business, with Americans spending more than $1 billion each year on supplements containing omega-3 fatty acids. These essential nutrients help build and maintain the connections between brain cells that support memory, learning, and other cognitive functions.

But a new study suggests that getting more omega-3s into the brain through supplements may not provide the protection many people expect.

Researchers at Keck Medicine of USC found that even when high doses of omega-3s successfully reached the brain, they did not produce measurable improvements in memory, thinking abilities, or protection against brain shrinkage.

The findings, published in eBioMedicine , come from a two-year clinical trial involving older adults considered to be at increased risk of developing Alzheimer's disease.…