The study examined the diets and dementia levels of nearly 900 men and women who participated in the Framingham Heart Study. Researchers followed the participants for nine years, and found that 99 people developed dementia, including 71 who developed Alzheimer's disease.
The researchers examined the participants' blood levels of docosahexaenoic acid (DHA) -- a polyunsaturated omega-3 fatty acid -- and found that those with the highest DHA levels had a 47 percent lower risk of developing dementia, and a 39 percent lower risk of developing Alzheimer's, compared to participants with lower blood DHA levels.
"If you have a high level of DHA, a fatty acid found in fish, it reduced your risk of dementia by about half," said the study's lead researchers, Dr. Ernst J. Schaefer, a senior scientist and director of the Lipid Metabolism Laboratory at the Jean Mayer U.S. Department of Agriculture Human Nutrition research Center on Aging at Tufts University.
Omega-3s have long been lauded as beneficial to cardiovascular and circulatory system health. "Just as fish is good for your heart, it's probably food for your brain as well," Schaefer said.
Schaefer's study found that blood levels of DHA can differ depending on the liver's ability to convert ALA (alpha-linolenic acid, another fatty acid) into DHA. However, the greatest influence on blood DHA levels was the amount of fish consumed. The Framingham participants who ate the most fish per week had the highest blood levels of DHA, while those who ate the least fish had much lower levels.
Though Schaefer believes supplementing the diet with fish oil capsules would be as effective as eating fatty fish -- such as mackerel, herring, lake trout, sardines, salmon and albacore tuna -- some experts believe more study is needed to determine the link between fish oil supplements and prevention of dementia.
According to consumer health advocate Mike Adams, author of "The Seven Laws of Nutrition," Schaefer's study shows that the oils found in fatty fish can protect the nervous system from degenerative damage.
"But what most people don't know is that those same healthy oils can also be found in many plants, including chia seeds, flaxseed, avocados and macadamia nuts," Adams said.