(CNN) - Scientists have long known that the Mediterranean diet can offer health benefits to those who follow it closely, including helping your heart, bones, brain and even longevity.
Now, a study suggests that adhering to the Mediterranean diet can help prolong your life, even if you are already 65 or older.
A Mediterranean diet involves eating plant-based meals, with just small amounts of lean meat and chicken and more servings of mostly vegetables, fruits, legumes, unrefined grains, olive oil and fish.
Closely adhering to such a diet was associated with a 25 percent lower risk of all-cause death among a sample of older adults in the Molise region of Italy, according to the study, which was published last week in the British Journal of Nutrition.
"We found, for the first time I believe, a dose-response relationship between the Mediterranean diet and mortality risk. That means that the greater adherence to this diet, the greater the benefit," said the study's first author, Marialaura Bonaccio, an epidemiologist at the Mediterranean Neuromed Institute, a hospital and research institute in Pozzilli, Italy.
The study did not explore exactly how the diet could be tied to prolonged life, but "the Mediterranean diet is rich in many anti-inflammatory foods, so for example, generally olive oil and fibers and also antioxidants," she said, which may play a role in improved longevity.
For the study, researchers tracked the health and diets of 5,200 people 65 and older. The adults were enrolled in the study between 2005 and 2010, and they were followed up with until December 31, 2015. Each adult's food intake in the year before enrollment was assessed in a food frequency questionnaire called EPIC.
The researchers measured each adult's adherence to the Mediterranean diet by giving them one point for consuming a food group in the diet, such as fruits and nuts, vegetables, legumes, fish, cereals or a ratio of more monounsaturated than saturated fats, and for moderated alcohol intake. Monounsaturated fat is a healthy fat found in olive oil and other plant foods.
The researchers found that one-point increase in each person's Mediterranean diet score was associated with a lower risk of death from all causes, as well as specifically from coronary artery disease.
During an average of eight years following up with the adults, there were 900 deaths among them, according to the researchers.
The researchers also reviewed what was known in scientific literature about the health benefits of the Mediterranean diet by performing a meta-analysis on six previously published studies.
In the meta-analysis as well as the researchers' own new results, they found that each one-point increment in the Mediterranean diet score was associated with a 5 percent lower risk of death from all causes.
"The main finding is that adherence to the Mediterranean diet is protective against all-cause mortality and also against some cardiovascular outcomes in a sample of elderly people," Bonaccio said.
"We found that one of the most important food groups is the consumption of monosaturated fats -- the main source is extra virgin olive oil, mainly -- over saturated fat consumption. That means you have to consume more than saturated," she said.
The study had some limitations, including that it was observational and found only an association between eating a Mediterranean diet and longevity, not a causal relationship. Another limitation was that food intake was self-reported.
Additionally, the meta-analysis included only a small number of studies.
All in all, Bonaccio said, "the novelty of the study is that we particularly looked at benefits for older people."
Because the study was conducted only in adults 65 and older, the findings can not be generalized to other age groups.
Yet the study confirms previous findings about the health benefits of a Mediterranean diet in older adults, said Mercedes Sotos-Prieto, an assistant professor of food and nutrition sciences at Ohio University and visiting scientist at Harvard T.H. Chan School of Public Health, who was not involved in the new research.
"There is strong evidence published over the last decades showing the health benefits of following a Mediterranean diet," she said.
For example, Sotos-Prieto was first author of a study published in The New England Journal of Medicine last year that showed a consistent association between adhering to an improved diet quality in general over 12 years and a significantly reduced risk of early death.
The study assessed improvements in diet quality based on the Mediterranean diet score, along with the 2010 Healthy Eating Index from the US Dietary Guidelines for Americans and the Dietary Approaches to Stop Hypertension diet from the US National Heart, Lung, and Blood Institute. It included 47,994 women and 25,745 men between 30 and 75 years old.
In other words, similar to the new study, this research also found prolonged life to possibly be associated with the Mediterranean diet.
Changes in diet were associated with up to a 16% lower mortality risk among those adults whose Mediterranean diet score improved over 12 years in comparison with those whose diet quality remained relatively stable, Sotos-Prieto said.
"The Mediterranean diet includes the healthy elements of a healthy eating pattern -- including consumption of fruits and vegetables, legumes, nuts, whole grains, olive oil, fish and low consumption of red and processed meats -- along with a Mediterranean lifestyle that includes enjoying meals with family and friends," she said. "The Mediterranean diet is an eating pattern that can be easily maintained for a long term, and that is reflected as well in the long-term benefits, including improving longevity."
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