The mediterranean diet which is high in vegetables, whole grains, fish, and olive oil not only helps you live longer but also keeps the brain sharper, say researchers, adding that those who followed the diet had the lowest risk of cognitive impairment.

According to a recent analysis of data from two major eye disease studies published in the journals Alzheimer's & Dementia, adherence to the Mediterranean diet correlates with higher cognitive function.

Dietary factors also seem to play a role in slowing cognitive decline.

Researchers at the National Eye Institute (NEI), part of the US National Institutes of Health (NIH), led the analysis of data from the Age-Related Eye Disease Study (AREDS) and AREDS2.

"We do not always pay attention to our diets. We need to explore how nutrition affects the brain and the eye" said lead authors of the studies Emily Chew, director of the NEI in the US.

For the findings, the research team examined the effects of nine components of the mediterranean diet on cognition.

The diet emphasises the consumption of whole fruits, vegetables, whole grains, nuts, legumes, fish, and olive oil, as well as reduced consumption of red meat and alcohol.

AREDS and AREDS2 assessed over the years the effect of vitamins on age-related macular degeneration (AMD), which damages the light-sensitive retina.

AREDS included about 4,000 participants with and without AMD, and AREDS2 included about 4,000 participants with AMD.

The researchers assessed AREDS and AREDS2 participants for diet at the start of the studies.

The AREDS study tested participants' cognitive function at five years, while AREDS2 tested cognitive function in participants at baseline and again two, four, and 10 years later.

The researchers assessed diet with a questionnaire that asked participants their average consumption of each Mediterranean diet component over the previous year.

Participants with the greatest adherence to the Mediterranean diet had the lowest risk of cognitive impairment. High fish and vegetable consumption appeared to have the greatest protective effect.

At 10 years, AREDS2 participants with the highest fish consumption had the slowest rate of cognitive decline.

The researchers also found that participants with the ApoE gene, which puts them at high risk for Alzheimer's disease, on average had lower cognitive function scores and a greater decline than those without the gene.

The benefits of close adherence to a Mediterranean diet were similar for people with and without the ApoE gene, meaning that the effects of diet on cognition are independent of genetic risk for Alzheimer's disease, the study said.