Greater adherence to the diet was associated with a 9% lower overall mortality, a 9% lower cardiovascular mortality, a 6% lower incidence of or mortality from cancer, and a 13% lower incidence of Parkinson's disease and Alzheimer's disease, Francesco Sofi, M.D., of the University of Florence, and colleagues reported online in the British Medical Journal.
The Mediterranean diet, widely reported to be a model of healthy eating, is rich in vegetables, fruits, legumes, cereals, fish, nuts, olive oil, and a moderate intake of red wine during meals, but is low in red meat, dairy products, and alcohol.
Until now the majority of studies of the Mediterranean diet have assessed single nutrients or food groups, a limited approach, the researchers said, because food components of diets offer synergistic and antagonistic interactions and because people eat a complex variety of nutrients.
Therefore, over the past few years an increasing number of studies have shifted to analyses of dietary patterns as a whole and it has proven effective against cardiovascular disease and cancer, the researchers wrote.
But to the best of their knowledge, the investigators said, theirs is the first report to systematically assess the possible association between adherence to the Mediterranean diet, mortality, and chronic diseases in the general population.
Their meta-analysis comprised 12 international prospective cohort studies that included 1,574,299 individuals followed for intervals of three to 18 years.
Data came from English and non-English publications in PubMed, Embase, the Cochrane register, and other registries from 1966 to June 30, 2008.
Only six of the 12 studies were done in Mediterranean populations. The remaining cohorts included U.S. populations, Northern Europeans, and a group of Europeans living in Australia.
All of the studies used an "adherence score," which varied from a minimum of zero points indicating low adherence to the Mediterranean diet to a maximum of seven to nine points reflecting high adherence.
The cumulative analysis among eight cohorts (514,816 individuals and 33,576 deaths) evaluating overall mortality showed that a two-point increase in the adherence score was significantly associated with a reduced risk of mortality (pooled relative risk 0.91, 95% confidence interval 0.89 to 0.94).
Likewise, the analyses showed a beneficial role for greater adherence to a Mediterranean diet on cardiovascular mortality (pooled relative risk 0.91, 95% CI 0.87 to 0.95), incidence of or mortality from cancer (0.94, 95% CI 0.92 to 0.96), and incidence of Parkinson's disease and Alzheimer's disease (0.87, 95% CI 0.80 to 0.96).
Study limitations included the fact that the Mediterranean diet is not a homogeneous pattern of eating. It is not clear how to group some food categories such as legumes, milk, and dairy products, the real importance of different types of meat, and definition of moderate amounts of alcohol intake.
In addition, the researchers said, the use of a score for estimating a dietary pattern is limited by subjectivity and the available data, while a further limitation exists in the different adjustments for potential confounders in the studies.
An overall analysis of these cohort studies found a significant drop in the risk of all the main clinical outcomes with increasing adherence to a Mediterranean diet. This seems to show that an adherence score based on a theoretically defined Mediterranean diet would be an effective preventive tool for reducing the risk of mortality and morbidity in the general population, the researchers said.
Unfortunately, they said, despite the worldwide promotion of the diet, there has been a progressive shift to a non-Mediterranean dietary pattern, even in countries bordering the Mediterranean sea.
The findings "confirm current guidelines and recommendations from all the major scientific associations that strongly encourage a Mediterranean-like dietary pattern for primary and secondary prevention of major chronic diseases," Dr. Sofi and colleagues concluded.
|No funding or competing individual interests were reported for this study.|
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine
British Medical JournalSource Reference: Sofi F, et al "Adherence to Mediterranean diet and health status: meta-analysis" BMJ 2008; 337: DOI: 10.1136/bmj.a1344.