The large trial, based on data from more than 74,000 healthy men and women in nine European countries, confirms previous, short cohort studies linking this diet to longer life expectancy.
People living around the Mediterranean typically eat lots of vegetables, fruits, and cereals, have a moderate to high intake of fish, and eat little saturated fat, preferring instead the unsaturated olive oil. They also have a low intake of dairy products and meat, and drink modest amounts of wine.
The high content of antioxidant nutrients in the fruit, vegetables and wine, and specific fatty acids in fish and olive oil, have been shown to fight off disease and ageing and could be responsible for this longevity.
Principal investigator on the project, Professor Antonia Trichopoulou from the University of Athens, and colleagues gathered information on diet, lifestyle, medical history, smoking and physical activity levels from the thousands of Europeans who had to be at least 60-years-old. They rated the subjects' adherence to a modified Mediterranean diet using a recognised scoring scale.
A higher dietary score was associated with a lower overall death rate, they write in the study, published in the BMJ online.
A two-point increase corresponded to an 8 per cent reduction in mortality, while a three or four point increase was associated with a reduction of total mortality by 11 per cent or 14 per cent respectively.
For example, a healthy man aged 60 who adheres well to the diet - getting a dietary score of 6-9 -can expect to live about one year longer than a man of the same age who does not adhere to the diet.
The association was strongest in Greece and Spain, probably because people in these countries follow a genuinely Mediterranean diet, said the authors.
They write that the study's prospective nature, its large size, its reliance on a European population sample, and the calibration of dietary exposures across countries were advantages over previous trials in this area. It also exploited the availability of information on several non-dietary variables and was able to control for them as potential confounders.
However the association of the score with non-nutritional variables was generally weak, they said, reducing the potential for such confounding.
Nevertheless they conclude that "adherence to a diet relying on plant foods and unsaturated lipids and that resembles the Mediterranean diet, may be particularly appropriate for elderly people, who represent a rapidly increasing group in Europe".