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Mediterranean Diet Improves Health & Mortality
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"reduction in overall mortality (9%), mortality from cardiovascular diseases (9%), incidence of or mortality from cancer (6%), and incidence of Parkinson's disease and Alzheimer's disease (13%). These results seem to be clinically relevant for public health, in particular for encouraging a Mediterranean-like dietary pattern for primary prevention of major chronic diseases."
Adherence to Mediterranean diet and health status: meta-analysis
BMJ Sept 2008
Francesco Sofi, researcher in clinical nutrition1,2,5, Francesca Cesari, researcher1, Rosanna Abbate, full professor of internal medicine1,5, Gian Franco Gensini, full professor of internal medicine3, Alessandro Casini, associate professor of clinical nutrition2,4,5
1 Department of Medical and Surgical Critical Care, Thrombosis Centre, University of Florence, Viale Morgagni 85, 50134 Florence, Italy, 2 Regional Agency for Nutrition, Azienda Ospedaliero-Universitaria Careggi, Florence, 3 Don Carlo Gnocchi Foundation, Onlus IRCCS, Impruneta, Florence, 4 Department of Clinical Pathophysiology, Unit of Clinical Nutrition, University of Florence, 5 Centro Interdipartimentale per la Ricerca e la Valorizzazione degli Alimenti (CeRA), University of Florence
ABSTRACT
Objective- To systematically review all the prospective cohort studies that have analysed the relation between adherence to a Mediterranean diet, mortality, and incidence of chronic diseases in a primary prevention setting.
Design- Meta-analysis of prospective cohort studies.
Data sources- English and non-English publications in PubMed, Embase, Web of Science, and the Cochrane Central Register of Controlled Trials from 1966 to 30 June 2008.
Studies- reviewed Studies that analysed prospectively the association between adherence to a Mediterranean diet, mortality, and incidence of diseases; 12 studies, with a total of 1 574 299 subjects followed for a time ranging from three to 18 years were included.
Results- The cumulative analysis among eight cohorts (514 816 subjects and 33 576 deaths) evaluating overall mortality in relation to adherence to a Mediterranean diet 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, 0.87 to 0.95), incidence of or mortality from cancer (0.94, 0.92 to 0.96), and incidence of Parkinson's disease and Alzheimer's disease (0.87, 0.80 to 0.96).
Conclusions- Greater adherence to a Mediterranean diet is associated with a significant improvement in health status, as seen by a significant reduction in overall mortality (9%), mortality from cardiovascular diseases (9%), incidence of or mortality from cancer (6%), and incidence of Parkinson's disease and Alzheimer's disease (13%). These results seem to be clinically relevant for public health, in particular for encouraging a Mediterranean-like dietary pattern for primary prevention of major chronic diseases.
Introduction
The Mediterranean diet, representing the dietary pattern usually consumed among the populations bordering the Mediterranean sea, has been widely reported to be a model of healthy eating for its contribution to a favourable health status and a better quality of life.1 2 Since the first data from the seven countries study,3 several studies in different populations have established a beneficial role for the main components of the Mediterranean diet on the occurrence of cardiovascular diseases and chronic degenerative diseases.2 4 However, research interest in this field over the past years has been focused on estimating adherence to the whole Mediterranean diet rather than analysing the individual components of the dietary pattern in relation to the health status of the population.5 This because the analyses of single nutrients ignore important interactions between components of a diet and, more importantly, because people do not eat isolated nutrients. Hence, dietary scores estimating adherence to a Mediterranean diet, devised a priori on the basis of the characteristic components of the traditional diet of the Mediterranean area, have been found to be associated with a reduction of overall mortality and mortality from cardiovascular diseases and cancer.6 The aim of this study was to do a systematic review with meta-analysis of all the available prospective cohort studies that have assessed the association between adherence to a Mediterranean diet and adverse outcomes, in order to establish the role of adherence to a Mediterranean diet in primary prevention.
Discussion
This meta-analysis shows, in an overall analysis comprising more than 1.5 million healthy subjects and 40 000 fatal and non-fatal events, that greater adherence to a Mediterranean diet is significantly associated with a reduced risk of overall mortality, cardiovascular mortality, cancer incidence and mortality, and incidence of Parkinson's disease and Alzheimer's disease. The cumulative analysis of 12 cohort studies shows that a two point increase in the score for adherence to a Mediterranean diet determines a 9% reduction in overall mortality, a 9% reduction in mortality from cardiovascular diseases, a 6% reduction in incidence of or mortality from neoplasm, and a 13% reduction in incidence of Parkinson's disease and Alzheimer's disease. To the best of our knowledge, this is the first report that has systematically assessed, through meta-analysis, the possible association between adherence to a Mediterranean diet, mortality, and the occurrence of chronic diseases in the general population.
Diet and disease
The effect of diet on human health has been amply reported in many epidemiological, population based, and randomised clinical trials, providing evidence that a dietary pattern rich in some beneficial food groups such as fruit, vegetables, whole grains, and fish can reduce the incidence of cardiovascular and neoplastic diseases.7 However, until now, the vast majority of studies followed the approach of assessing single nutrients or food groups in relation to the occurrence of disease.4 8 9 This approach seems to have several conceptual and methodological limitations, because food components of diet present synergistic and antagonist interactions and because people eat a complex of nutrients.5 Therefore, over the past few years, researchers have shifted their attention from the evaluation of single nutrients to the analysis of dietary pattern as a whole.6 w1-w10 As a result, an increasing number of studies have been done by summing foods considered to be important for health to provide an overall measure of dietary quality-that is, a quality diet score.6
In this context, a prominent position has been occupied by studies evaluating adherence to a Mediterranean diet, because of its well known and evidence based beneficial effects on human health. Indeed, since the early 1970s many investigators have reported the beneficial role of the Mediterranean diet, as originally reported by Keys in the pioneering seven countries study.3 A diet rich in fruits, vegetables, legumes, and cereals, with olive oil as the only source of fat, moderate consumption of red wine especially during meals, and low consumption of red meat has been shown to be beneficial for all cause and cardiovascular mortality, lipid metabolism, blood pressure, and several different disease states such as endothelial dysfunction and overweight.7
Practical implications
In this study we aimed to systematically analyse all the prospective cohort studies that evaluated the effect of a computational score estimating adherence to a Mediterranean diet on health status. From the overall analysis of 11 cohort studies, of which eight assessed the risk of overall mortality, four assessed cardiovascular mortality, six assessed incidence of or mortality from neoplasm, and three assessed incidence of Parkinson's disease and Alzheimer's disease, we report a significant reduction in risk of all the main clinical outcomes with an increasing score for adherence to a Mediterranean diet. This observation seems to show that a score based on a theoretically defined Mediterranean diet is an effective preventive tool for measuring the risk of mortality and morbidity in the general population.
A Mediterranean diet has been shown to have a beneficial effect on the occurrence of diseases in industrialised and non-industrialised countries. All the major scientific associations, in fact, strongly encourage people to consume a Mediterranean-like dietary pattern to reduce their risk of disease.10 11 12 Unfortunately, despite this worldwide promotion of the Mediterranean diet, a progressive shift to a non-Mediterranean dietary pattern, even in countries bordering the Mediterranean sea, has progressively developed.13 It thus seems urgent to identify an effective preventive strategy to decrease the risk burden related to dietary habits in the general population; the use of such a tool could be important in increasing the implementation of dietary guidelines.
Limitations
Some limitations of this study can be identified. The Mediterranean diet is not a homogeneous pattern of eating, and heterogeneity on the score items exists. How to group some food categories such as legumes, nuts, and milk and dairy products; the real importance of different types of meat; and the establishment of the moderate amount of alcohol intake are still matters of dispute among researchers and can differ among the selected studies. None the less, the key characteristics of a Mediterranean diet were present in all the studies, and the overall analysis seemed not to be significantly influenced by these differences. In addition, the use of a score for estimating a dietary pattern is limited by subjectivity, conditioned by the available data and the main objectives of the study, and so possibly determining a great variability in the interpretation of the results.
Finally, a further limitation exists in the different adjustment for potential confounders seen among the included studies. This difference could have determined a residual confounding within the studies, especially for the non-Mediterranean cohorts. However, the sensitivity analysis according to the quality of the studies, which also included the presence or not of adjustment factors, showed no significant influence of residual confounding on the overall findings of our meta-analysis.
Conclusions
This meta-analysis shows that adherence to a Mediterranean diet can significantly decrease the risk of overall mortality, mortality from cardiovascular diseases, incidence of or mortality from cancer, and incidence of Parkinson's disease and Alzheimer's disease. These results seem to be clinically relevant in terms of public health, particularly for reducing the risk of premature death in the general population, and are strictly concordant with 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.
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