Accruing evidence on benefits of adherence to the Mediterranean diet on health: an updated systematic review and meta-analysis1,2
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Accruing evidence on benefits of adherence to the Mediterranean diet
on health: an updated systematic review and meta-analysis1,2
Francesco Sofi, Rosanna Abbate, Gian Franco Gensini, and Alessandro Casini
ABSTRACT great deal of attention has been given to tools that estimate the
Background: The Mediterranean diet has long been reported to adherence of individuals to the Mediterranean diet because of the
be protective against the occurrence of several different health usefulness of these tools to identify the whole dietary pattern
outcomes. instead of single foods or nutrients (4). Hence, computational
Objective: We aimed to update our previous meta-analysis of pub- scores have been created and used in several large epidemiologic
lished cohort prospective studies that investigated the effects of studies to seek whether they could be useful to estimate the risk of
adherence to the Mediterranean diet on health status. disease in the general population (5). Some large epidemiologic
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Design: We conducted a comprehensive literature search through studies conducted in different cohorts evidenced an association
electronic databases up to June 2010. between a greater adherence to Mediterranean diet, a reduced risk
Results: The updated review process showed 7 prospective studies of mortality, and the incidence of major chronic diseases (6–9). In
published in the past 2 y that were not included in the previous 2008, we performed a meta-analysis that included all cohort
meta-analysis (1 study for overall mortality, 3 studies for cardiovas- prospective studies that investigated this issue, and we observed
cular incidence or mortality, 1 study for cancer incidence or mor- that a 2-point increase of adherence to Mediterranean diet
tality, and 2 studies for neurodegenerative diseases). These recent conferred a significant protection against mortality, the occur-
studies included 2 health outcomes not previously investigated (ie, rence of cardiovascular diseases, and major chronic degenerative
mild cognitive impairment and stroke). The meta-analysis for all diseases (3). However, the previous meta-analysis is 3 y old, and
studies with a random-effects model that was conducted after the more prospective cohort studies have since been published.
inclusion of these recent studies showed that a 2-point increase in Therefore, the aim of this study was to update our previous
adherence to the Mediterranean diet was associated with a signifi-
systematic review and meta-analysis conducted in cohort pro-
cant reduction of overall mortality [relative risk (RR) = 0.92; 95%
spective studies that investigated the effects of adherence to
CI: 0.90, 0.94], cardiovascular incidence or mortality (RR = 0.90;
Mediterranean diet on several health outcomes and to use these
95% CI: 0.87, 0.93), cancer incidence or mortality (RR = 0.94;
data to conduct a meta-regression analysis to explore a potential
95% CI: 0.92, 0.96), and neurodegenerative diseases (RR = 0.87;
source of heterogeneity in studies.
95% CI: 0.81, 0.94). The meta-regression analysis showed that sam-
ple size was the most significant contributor to the model because it
significantly influenced the estimate of the association for overall METHODS
mortality.
Conclusion: This updated meta-analysis confirms, in a larger num- Literature search
ber of subjects and studies, the significant and consistent protection According to the statement of the Preferred Reporting Items for
provided by adherence to the Mediterranean diet in relation to the Systematic Reviews and Meta-Analyses (10), we systematically
occurrence of major chronic degenerative diseases. Am J Clin searched published cohort prospective studies that investigated
Nutr 2010;92:1189–96. the association between adherence to the Mediterranean diet and
health outcomes in electronic databases: MEDLINE (source:
PubMed, 1966 to June 2010; www.pubmed.com), EMBASE (1980
INTRODUCTION to June 2010; www.embase.com), Web of Science (isiweb
The Mediterranean diet has long been reported to be the ofknowledge.com), The Cochrane Library (source: The Cochrane
optimal diet for preventing noncommunicable diseases and
1
preserving good health (1–3). The Mediterranean-style diet is not From the Department of Medical and Surgical Critical Care, Thrombo-
a specific diet, but rather a collection of eating habits traditionally sis Centre, University of Florence, Florence, Italy (FS, RA, and GFG); the
followed by people in the different countries bordering the Agency of Nutrition, Azienda Ospedaliero-Universitaria Careggi, Florence,
Mediterranean Sea. The diet refers to a dietary profile commonly Italy (FS and AC); and the Don Carlo Gnocchi Foundation, Centro Santa
Maria agli Ulivi, Onlus IRCCS, Florence, Italy (FS and GFG).
available in the early 1960s in the Mediterranean regions and 2
Address correspondence to F Sofi, Department of Medical and Surgical
characterized by a high consumption of fruit, vegetables, le- Critical Care, Thrombosis Centre, University of Florence, Viale Morgagni
gumes, and complex carbohydrates, with a moderate consump- 85, 50134 Florence, Italy. E-mail: francescosofi@gmail.com.
tion of fish, and the consumption of olive oil as the main source of Received April 14, 2010. Accepted for publication July 27, 2010.
fats and a low-to-moderate amount of red wine during meals. A First published online September 1, 2010; doi: 10.3945/ajcn.2010.29673.
Am J Clin Nutr 2010;92:1189–96. Printed in USA. Ó 2010 American Society for Nutrition 11891190 SOFI ET AL
Central Register of Controlled Trials, 2010, issue 2; www.the ment for confounders that include demographic, anthropometric,
cochranelibrary.com/), clinicaltrials.org, and Google Scholar and traditional risk factors were considered of high quality.
(scholar.google.com). Relevant keywords relating to the Medi-
terranean diet in combination as MeSH terms and text words
(“Mediterranean diet,” or “diet” or “dietary pattern” “Mediterra- Statistical analyses
nean,” or “adherence” or “score” and their variants) were used in We used the Review Manager program (RevMan, version
combination with words relating to health status (“health,” or 5.0.18 for Macintosh, 2008; The Cochrane Collaboration,
“mortality” or “morbidity,” or “cardiovascular diseases,” or Copenhagen, Denmark) and the Statistical Package for Social
“neoplastic diseases,” or “cancer,” or “neoplasm,” or “de- Sciences software (SPSS, version 18.0 for Macintosh; SPSS,
generative diseases,” or “Alzheimer’s disease,” or “Parkinson’s Chicago, IL) to pool and analyze results from the individual
disease,” or “cerebrovascular disease,” or “dementia,” or “cog- studies. The methods and results of all recently identified cohort
nition disorder,” or “stroke,” or “outcome,” or “prospective,” or prospective studies were added to the previous table, and data
“follow-up,” or “cohort” and their variants). The search strategy were formally combined. Pooled results were reported as relative
had no language restrictions. References from the extracted articles risks (RRs) and presented with 95% CIs with 2-sided P values by
and reviews were also consulted to complete the data bank. When using a random-effects model (DerSimonian and Laird method)
multiple articles for a single study were present, we used the latest and the general variance-based method. P , 0.05 was consid-
publication and supplemented it, if necessary, with data from the ered statistically significant. When available, we used the results
most complete or updated publication. of the original studies from multivariate models with the most
complete adjustment for potential confounders; the confounding
variables included in the analyses are shown in Table 1.
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Study selection Statistical heterogeneity was evaluated by using the I2 statistic,
We identified studies that prospectively evaluated the asso- which assessed the appropriateness of pooling the individual
ciation of an a priori score used for assessing adherence to study results. The I2 value provided an estimate of the amount of
Mediterranean diet and adverse clinical outcomes. We excluded variance across studies because of heterogeneity rather than
studies if they had a cross-sectional or case-control design, if they chance. Where I2 was .50%, the heterogeneity was considered
analyzed adherence to a nonspecific dietary pattern or to a rec- substantial. A small study bias or publication bias was appraised
ommended dietary guideline and not to Mediterranean diet, if by visual inspection of the funnel plot of effect size against the
they evaluated cohort of patients who suffered from a prior SE and, analytically, by the Egger’s test. Moreover, to in-
clinical event (ie, in a secondary prevention), if they did not adjust vestigate possible sources of heterogeneity across studies, we
for potential confounders, and if they did not report an adequate performed a meta-regression analysis to investigate the effects
statistical analysis. of various characteristics of studies on the study estimates of
RRs.
Data extraction
Two investigators (FS and AC) assessed potentially relevant RESULTS
articles for eligibility. The decision to include or exclude studies The updated search from recent years resulted in the identi-
was hierarchical and initially made on the basis of the study title, fication of 7 additional prospective studies (11–17) published up
then of the study abstract, and finally of the complete study to June 2010 that were not identified and included previously.
manuscript. Two researchers independently completed searches, Characteristics of these recent studies are displayed in Table 1. Of
identification of studies, data abstraction, and tabulation, and these, 1 study presented the overall mortality as a clinical out-
discordances were resolved by discussions. The following base- come (14), 3 studies presented the incidence and/or mortality
line characteristics were extracted from the original articles by from cardiovascular diseases (13, 15, 16), 1 study presented the
using a standardized data extraction form and included in the incidence and/or mortality from neoplastic diseases (17), and 2
meta-analysis: lead author, year of publication, cohort name, studies presented the incidence of neurodegenerative diseases
country of origin of the cohort, sample size of the cohort, number (11, 12). Notably, 2 of the 7 studies reported clinical outcomes not
of outcomes, duration of follow-up, age at entry, sex, outcomes, previously investigated, such as mild cognitive impairment and
components of the Mediterranean diet adherence score, and stroke (12, 13). On the other hand, one study was an updated
variables that entered into the multivariable model as potential analysis of a study already reported in the previous meta-analysis
confounders (Table 1). for the overall mortality outcome; therefore, only the most
Outcomes of interests were overall mortality, mortality and/or updated study was added to this updated final analysis (14). Taken
incidence from cardio- and cerebrovascular diseases, mortality altogether, a total of 18 cohort prospective studies were included
and/or incidence from cancer, and incidence of neurodegenera- and entered into the final analysis. As a whole, the updated
tive diseases. analysis determined a study population that reached a total of
2,190,627 subjects analyzed. Included samples ranged in size
from 161 to 485,044, with a follow-up time that ranged from 4 to
Quality assessment 20 y.
Study quality was assessed according to the following criteria: Considerable variations among studies were observed in the
1) number of study participants, 2) duration of follow-up, and 3) number of participants, sex and age of participants, length of
adjustment for potential confounders. Studies with a high follow-up, and dietary components used to measure the adher-
number of participants, long duration of follow-up, and adjust- ence score to the Mediterranean diet. Studies conducted inTABLE 1
Study characteristics of the recent prospective studies investigating adherence to the Mediterranean diet and health outcomes1
Author, year (cohort) Country Sample size/total cohort Outcome Follow-up Age Sex Components of the adherence score Adjustment
n/total n y y
Feàrt et al, France 50/1410 Alzheimer 5 68–952 M/F 1) High legume intake Age, sex, BMI, hypertension,
2009 (11) disease 2) High whole-grain products intake hypercholesterolemia,
(Three-City 3) High fruit intake smoking habit, education,
Study) 4) High vegetable intake marital status, total energy,
5) High fish intake physical activity, medications,
6) High MUFA:SFA ratio depression, apoE genotype,
7) Moderate alcohol consumption and stroke
8) Low red and processed meat intake
9) Low dairy product intake
Scarmeas et al, United States 241/1199 Mild 4.5 76.73 M/F 1) High legume intake Age, sex, ethnicity, education,
2009 (12) (only in those cognitive 2) High cereal intake apoE genotype, total energy,
(Washington who were impairment 3) High fruit intake and BMI
Heights- cognitively 4) High vegetable intake
Inwood normal at 5) High fish intake
Columbia baseline) 6) High MUFA:SFA ratio
Aging 7) Moderate alcohol consumption
Project) 8) Low meat intake
9) Low dairy product intake
Fung et al, United States 2391/74,886 CHD 20 38–63 F 1) High legume intake Age, smoking habit, BMI,
2009 1763/74,886 Stroke 2) High whole-grain products intake menopausal status, hormone
(13) (Nurses’ 3) High fruit intake use, total energy, multivitamin
Health 4) High vegetable intake intake, alcohol, family history,
Study) 5) High fish intake physical activity, and
6) High nuts intake aspirin use
7) High MUFA:SFA ratio
8) Moderate alcohol consumption
9) Low red and processed meat intake
UPDATED META-ANALYSIS ON MEDITERRANEAN DIET
Trichopoulou Greece 1075/23,349 Overall 8.5 20–86 M/F 1) High legume intake Age, sex, education, smoking
et al, 2009 mortality 2) High cereal intake habit, waist:hip ratio, MET
(14) (EPIC- 3) High fruit/nuts intake score, total energy, and BMI
Greece) 4) High vegetable intake
5) High fish intake
6) High MUFA:SFA ratio
7) Moderate alcohol consumption
8) Low meat and poultry intake
9) Low dairy product intake
(Continued)
1191
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TABLE 1 (Continued )
Author, year (cohort) Country Sample size/total cohort Outcome Follow-up Age Sex Components of the adherence score Adjustment
n/total n y y
Buckland et al, Spain 606/40,151 CHD 10.4 29–69 M/F 1) High legume intake Age, education, BMI, physical
2009 (15) 2) High cereal intake activity, smoking habit,
(EPIC Spain) 3) High fruit/nuts intake diabetes, hypertension,
4) High vegetable intake hyperlipidemia, and total
5) High fish intake energy
6) High MUFA:SFA ratio
7) Moderate alcohol consumption
8) Low meat and poultry intake
9) Low dairy product intake
Martı́nez-González Spain 100/13,609 CVD 4.9 383 M/F 1) High legume intake Age, sex, family history of CVD,
et al, 2010 (16) 2) High cereal intake total energy, physical activity,
(SUN Study) 3) High fruit/nuts intake smoking habit, BMI, diabetes,
4) High vegetable intake aspirin, hypertension, and
5) High fish intake hypercholesterolemia
6) High MUFA:SFA ratio
SOFI ET AL
7) Moderate alcohol consumption
8) Low meat and poultry intake
9) Low dairy product intake
Buckland et al, United Kingdom, 449/485,044 Gastric 8.9 35–70 M/F 1) High legume intake Age, sex, BMI, education,
2010 (17) France, Denmark, adenocarcinoma 2) High cereal intake smoking habit, and total
(Spanish cohort Sweden, Germany, 3) High fruit/nuts intake energy
of the EPIC-Heart Italy, Spain, 4) High vegetable intake
Study) Netherlands, 5) High fish intake
Norway, and 6) High olive oil intake
Greece 7) Moderate alcohol consumption
8) Low meat and poultry intake
9) Low dairy product intake
1
MUFA, monounsaturated fatty acid; SFA, saturated fatty acid; CHD, coronary heart disease; EPIC, European Prospective Investigation into Cancer and Nutrition; MET, metabolic equivalent tasks; SUN,
Seguimiento Universidad de Navarra; CVD, cardiovascular disease.
2
Range (all such values).
3
Mean.
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European countries increased to 9 studies (50% of the total from and incidence of neoplastic diseases (Figure 3), a greater
number of studies included). adherence to the Mediterranean diet still determined a signifi-
By grouping the studies according to the different clinical cant amount of protection, with a similar extent than that of
outcomes, the overall mortality did not change for the number previous meta-analysis (RR = 0.94; 95% CI: 0.92, 0.96; P ,
of studies evaluated (ie, 9 studies that included an updated 0.00001) and again no significant heterogeneity (I2 = 6%; P =
analysis of the Greek cohort of the EPIC (European Prospective 0.38). The results of the previous meta-analysis were also
Investigation into Cancer and Nutrition) with a total of 514,118 confirmed for the occurrence of neurodegenerative diseases
subjects and 34,322 deaths, whereas a consistent increase of (Figure 4), which extended to mild cognitive impairment, with
studies and subjects analyzed for the other clinical outcomes a 13% reduced risk of individuals who most adhered to the
has been reported. Indeed, cardiovascular mortality and in- Mediterranean diet (RR = 0.87; 95% CI: 0.81, 0.94; P ,
cidence were consistently augmented by the number of studies 0.00001) and no significant heterogeneity across studies (I2 =
and subjects analyzed, with a total of 7 cohorts, 534,064 0%; P = 0.73).
subjects, and 8739 deaths or incident cases. Similarly, the
mortality from and incidence of neoplastic diseases reached
1,006,410 subjects and 11,378 events, whereas the number of Publication bias
studies that evaluated the association between adherence to the
Mediterranean diet and neurodegenerative diseases increased The funnel plots of effect sizes compared with SEs that were
from 3 to 5 cohorts, with a total of 136,235 subjects and 1074 performed to investigate possible publication biases were sym-
cases, including an additional clinical outcome such as mild metric for all different clinical outcomes, which suggested the
cognitive impairment. absence of possible publication biases.
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Meta-analysis Meta-regression analysis
Meta-analytic pooling under a random-effects model con- Finally, to investigate the effects of various study character-
firmed the already reported significant association between a 2- istics on the study estimates of the RRs, we conducted a meta-
point increased adherence to the Mediterranean diet and a reduced regression analysis by grouping studies according to some
risk of mortality from all causes (RR = 0.92; 95% CI: 0.90, 0.94; characteristics, such as the number of subjects studied, number of
P , 0.00001) (Figure 1) with no evidence of statistical cases observed, country of origin of the patients, age of the
heterogeneity across studies (I2 = 33%; P = 0.15). When studies patients, and length of follow-up. The sample size of the included
that evaluated different clinical outcomes were grouped, we studies was the only contributor to the protection compared with
observed that a 2-point increase of adherence to the Mediter- the overall mortality (b = 0.059 6 0.018; P = 0.013) in the
ranean diet still remained associated with a reduced risk of present model. By plotting the estimates of associations for
mortality from and incidence of cardiovascular diseases (RR = overall mortality with the number of subjects analyzed for each
0.90; 95% CI: 0.87, 0.93; P , 0.00001) (Figure 2), which study, it was shown that the average protection compared with
showed no significant heterogeneity across studies (I2 = 35%; the overall mortality was reached with studies that investigated
P = 0.15). Likewise, in studies that investigated the mortality .2000 subjects (Figure 5).
FIGURE 1. Forest plot of the association between a 2-point increase of adherence score to the Mediterranean diet and the risk of all-cause mortality. The
center of each square indicates the relative risk of the study, and the horizontal lines indicate 95% CIs. The area of the square is proportional to the amount of
information from the study. The diamond indicates pooled estimates.1194 SOFI ET AL
FIGURE 2. Forest plot of the association between a 2-point increase of adherence score to the Mediterranean diet and the risk of mortality from or
incidence of cardiovascular diseases. The center of each square indicates the relative risk of the study, and the horizontal lines indicate 95% CIs. The area of
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the square is proportional to the amount of information from the study. The diamond indicates pooled estimates. CHD, coronary heart disease.
DISCUSSION neurodegenerative diseases. Furthermore, in this updated meta-
In this updated meta-analysis of prospective studies that in- analysis, which included 7 articles published in the past 3 y that
vestigated the association between adherence to the Mediterranean could not be considered in the previous meta-analysis, some other
diet and health status, findings were pooled from .2 million clinical outcomes, such as stroke and mild cognitive impairment,
subjects and 50,000 deaths or incident cases from any causes and/ were included, and a meta-regression analysis to investigate the
or from any cardiovascular, neoplastic, and neurodegenerative possible role of confounding factors was also conducted.
diseases. We confirmed the results of our previously published Several studies over the past decades showed the Mediterra-
meta-analysis, which suggested a significant protection against nean diet to be significantly associated with different health
major chronic degenerative diseases for subjects who reported outcomes, such as a favorable health status, better biochemical
a greater adherence to the Mediterranean diet (3). Indeed, a 2- profile, and quality of life (1–3, 26, 27). Accordingly, over-
point increase of adherence to the Mediterranean diet significantly whelming evidence on the health effects of such a dietary profile
determined a 8% reduction of death from any causes, a 10% re- has been reported in many different study cohorts by stimulating
duction from death and/or incidence of cardio- and cerebrovas- both scientific and lay communities to promote this dietary
cular diseases, a 6% reduction from death and/or the incidence pattern as the ideal dietary pattern for preventing non-
of neoplastic diseases, and a 13% reduction of the incidence of communicable diseases (3, 27).
FIGURE 3. Forest plot of the association between a 2-point increase of adherence score to the Mediterranean diet and the risk of mortality from or
incidence of neoplastic diseases The center of each square indicates the relative risk of the study, and the horizontal lines indicate 95% CIs. The area of the
square is proportional to the amount of the information from the study. The diamond indicates pooled estimates.UPDATED META-ANALYSIS ON MEDITERRANEAN DIET 1195
FIGURE 4. Forest plot of the association between a 2-point increase of adherence score to the Mediterranean diet and the risk of incidence of
neurodegenerative diseases. The center of each square indicates the relative risk of the study, and the horizontal lines indicate 95% CIs. The area of the
square is proportional to the amount of the information from the study. The diamond indicates pooled estimates.
In this context, with the aim of identifying a practical tool to the interest of researchers on this issue rose, and a total of 7 new
estimate how populations follow the guidelines of Mediterranean cohort prospective studies were added to the literature (11–17).
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diet, adherence scores were computed (4). Many different scores On the other hand, the issue has been shown to be of extreme
were created and tested in different study cohorts, but the most interest for the general population as well as for health admin-
important was definitely that created in 1995 and developed in istrators and governments for better tailoring their prevention
its final form in 2003 by Trichopoulou et al (6, 18). In their strategies and policies.
studies, which investigated the Greek cohort of the EPIC study, The present updated meta-analysis has some advantages with
Trichopoulou et al showed, for the first time to our knowledge, respect to the previous one: first, it present, to out knowledge, the
a significant association between an increase of such an adher- most comprehensive and updated assessment on this issue, with
ence score and the reduction of overall mortality. Subsequently, inclusion of new studies and an update of previously reported
many studies that used this kind of epidemiologic approach have studies; second, the association between the Mediterranean diet
been released by extending the evidence to many different health and health outcomes was extended to other relevant disease states
outcomes (3). that were not previously investigated, such as stroke and mild
The results of the first meta-analysis published in 2008, which cognitive impairment. These clinical outcomes are of clinical
comprised a total of 12 studies and .1.5 million subjects, were relevance for the ever-increasing age of the general population.
that a 2-point increase of score that estimated adherence to the Third, it reinforces the findings that a slight increase of the
Mediterranean diet significantly determined protection com- adherence score to the Mediterranean diet, as was observed by an
pared with premature death and various diseases. In the past 3 y, increase of 2 points of the adherence score, is significantly
FIGURE 5. Meta-regression analysis of the relation between sample sizes of the studies and all-cause mortality. The area of the circle is proportional to the
number of subjects studied in the study; the dashed line indicates the overall estimate of the association for studies that investigated all-cause mortality.1196 SOFI ET AL
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The authors’ responsibilities were as follows—FS and AC: conception and
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