The findings are the latest in a string of health benefits linked to the eating plan of the people of southern Europe, which has in the past also been associated with the prevention of Alzheimer's disease.
Published in today's issue of Neurology, the medical journal of the American Academy of Neurology, the new findings were based on researchers' observations of 192 Alzheimer sufferers for four and a half years.
During that time, 85 of the people died. Researchers found that those patients who most closely followed a Mediterranean diet were 76 percent less likely to die during the study period than those who followed the diet the least.
"The more closely people followed the Mediterranean diet, the more they reduced their mortality," said study author Nikos Scarmeas of Columbia University Medical Center in New York, and member of the American Academy of Neurology.
"For example, Alzheimer's patients who adhered to the diet to a moderate degree lived an average 1.3 years longer than those people who least adhered to the diet. And those Alzheimer's patients who followed the diet very religiously lived an average four years longer."
Previous research by Scarmeas published last year found that greater adherence to a Mediterranean-style diet could cut the risk of healthy people developing Alzheimer's disease by 68 percent.
The Med diet is rich in cereals, wine, fruits, nuts, legumes and whole grains, fish and olive oil. Its main nutritional components include beta-carotene, vitamin C, tocopherols, polyphenols , and essential minerals. It is these antioxidants and polyphenols that appear to offer protection, suggested the researchers.
Another study by the same researchers, published earlier last year in the Annals of Neurology (Vol. 59, pp. 912 - 921), reported that elderly individuals whose diet closely resembled the Med diet had a 40 per cent lower risk of Alzheimer's than those who adhered the least to the diet.
"New benefits of this diet keep coming out," wrote Scarmeas today.
"We need to do more research to determine whether eating a Mediterranean diet also helps Alzheimer's patients have slower rates of cognitive decline, maintain their daily living skills, and have a better quality of life."
Alzheimer's disease is the most common form of dementia and currently affects over 13 million people worldwide. The direct and indirect cost of Alzheimer care is over $100 bn (€ 81 bn) in the US alone. The direct cost of Alzheimer care in the UK was estimated at £15 bn (€ 22 bn, $30bn).
The Mediterranean diet has also been linked to longer life, less heart disease, and protection against some cancers - and the flow of scientific back-up for its healthfulness has started to trickle into consumer consciousness, with more and more people seeking out products that meet the diet's criteria.
Common foods of the eating plan include bread, pasta, rice, couscous and potatoes; olives, avocados and grapes; eggplant, tomatoes, peppers, nuts and beans; and cheese and yogurt. Moderate consumption of fish and poultry is also encouraged, whereas consumption of red meat is advised only a few times a month.
In the US, a nutrition group recently launched a Med Mark symbol to allow manufacturers to flag up Mediterranean diet foods. Introduced three months ago by Oldways, the packaging symbol already appears on 50 products.
To access a Mediterranean diet pyramid, listing foods that form part of the nutrition plan, click here .