Fish, vegetables, whole grains in diet can reduce dementia risk by 45%

Sticking to the Mediterranean diet may improve brain health, a new analysis suggests.

In findings published Tuesday in the journal Alzheimer's and Dementia, researchers from the National Eye Institute report that adults who adhere to the diet -- which emphasizes consumption of plant-based foods like fruits, vegetables, beans, nuts, herbs and whole grains -- were 45 percent less likely to show evidence of cognitive decline on several measures than those went off the meal plan.

"We do not always pay attention to our diets. We need to explore how nutrition affects the brain and the eye," co-author Dr. Emily Chew, director of the NEI's Division of Epidemiology and Clinical Applications, said in a statement.

Roughly 16 million Americans are living with some level of cognitive impairment, according to the U.S. Centers for Disease Control, research efforts designed to develop potential cures -- or at least ways to slow its progression -- have been ramped up in recent years as the population of those affected continues to grow.

For the study, Chew and her colleagues examined the effects of nine components of the Mediterranean diet on cognition. The diet emphasizes consumption of whole fruits, vegetables, whole grains, nuts, legumes, fish and olive oil, as well as reduced consumption of red meat and alcohol. Moderate amounts of dairy, poultry and eggs are also key to the Diet, as is seafood.

They analyzed data from two major eye disease studies: the Age-Related Eye Disease Study, or AREDS, and AREDS2. The two studies assessed the effect of vitamins on age-related macular degeneration, or AMD, a disease that damages the light-sensitive retina. AREDS included approximately 4,000 participants with and without AMD, while AREDS2 enrolled approximately 4,000 participants with AMD.

The researchers assessed AREDS and AREDS2 participants for diet at the start of the studies, and tested AREDS study participants' cognitive function after five years. Participants in AREDS2 had their cognitive function tested at baseline and again two, four and 10 years later.

Cognitive function was assessed using standardized tests based on the Modified Mini-Mental State Examination, as well as other tests. They assessed diets with a questionnaire that asked participants their average consumption of each Mediterranean diet component over the previous year.

In general, participants with the greatest adherence to the Mediterranean diet had the lowest risk of cognitive impairment. High consumption of fish and vegetable appeared to have the greatest protective effect, while, at 10 years, AREDS2 participants with the highest fish consumption had the slowest rate of cognitive decline.

However, the numerical differences in cognitive function scores between participants with the highest versus lowest adherence to a Mediterranean diet were relatively small, according to the authors. This means that individuals likely won't see a difference in daily function.

The researchers also found that participants with the ApoE gene -- which has been linked with increased risk for Alzheimer's disease -- had lower cognitive function scores and greater decline on average than those without the gene. Still, the benefits of close adherence to a Mediterranean diet were similar for this with and without the gene, meaning that the effects of diet on cognition are independent of genetic risk for Alzheimer's disease