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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.
Methods
Data sources
We focused on prospective studies investigating the association between adherence to a Mediterranean diet and health outcomes. We searched PubMed, Embase, Web of Science, and the Cochrane Central Register of Controlled Trials databases up to 30 June 2008, using a search strategy that included both truncated free text and exploded MeSH terms. MeSH headings included "Mediterranean", "diet", "dietary pattern", "disease", "health", "cardiovascular disease", "cerebrovascular disease", "coronary heart disease", "degenerative diseases", "cancer", "neoplasm", "prospective", "follow-up", or "cohort", and their variants. The search strategy had no language restrictions. We also consulted references from the extracted articles and reviews to complete the data bank. When multiple articles for a single study were present, we used the latest publication and supplemented it, if necessary, with data from the most complete...