The largest study to date, published in Neurology, finds that an increased consumption of foods that contain omega-3 fatty acids in conjunction with the avoidance of saturated fats, meat and dairy foods may be linked to preserving memory and thinking abilities in healthy people.
"Since there are no definitive treatments for most dementing illnesses, modifiable activities, such as diet, that may delay the onset of symptoms of dementia are very important," said study leader Dr Georgios Tsivgoulis.
Tsivgoulis, of both the University of Alabama at Birmingham, USA, and the University of Athens, Greece, suggested that, in healthy people, those who more closely followed the Mediterranean diet were 19% less likely to develop problems with their thinking and memory skills.
However, the authors noted that similar associations were not found in people with diabetes.
"Diet is an important modifiable activity that could help in preserving cognitive functioning in late life," said Tsivgoulis.
"However, it is only one of several important lifestyle activities that might play a role in late-life mental functioning," said the lead researcher - noting that exercise, avoiding obesity, not smoking and taking medications for conditions like diabetes and hypertension also play important roles.
The new data comes from the REasons for Geographic and Racial Differences in Stroke (REGARDS) study - a US national sample of the general population.
In the research, dietary information from 17,478 African-American and Caucasian people with an average age of 64 was reviewed to assess how closely they adhered to a Mediterranean diet. The participants were then tested to measure memory and thinking abilities over an average of four years.
Tsivgoulis and his colleagues found that 7% of the participants developed impairments in their thinking and memory skills during the study - noting that there was not a significant difference in declines between African-Americans and Caucasians.
The team found that adherence to the Mediterranean diet was associated with a 19% lower risk of thinking and memory problems in healthy people.
However, the researchers added that there was no significant association between diet and memory markers in people with diabetes - who accounted for around 17% of the study population.
Volume 80, Number 18, Pages 1684-1692, doi: 10.1212/WNL.0b013e3182904f69
"Adherence to a Mediterranean diet and risk of incident cognitive impairment"
Authors: Georgios Tsivgoulis, Suzanne Judd, Abraham J. Letter, Andrei V. Alexandrov, et al