Pulmonology · Medical Literature
The impact of Mediterranean diet adherence on allergic diseases: a systematic review and meta-analysis.
Abstract
Allergies are a growing public health concern worldwide. This meta-analysis investigated the association between adherence to the Mediterranean diet (MD) and the occurrence/severity of respiratory allergic conditions. Electronic databases (PubMed, Scopus, Science Direct, and EBSCO) were searched for studies published up to April 2024. Eligible studies reported OR with 95% CI for asthma, wheezing (respiratory symptom associated with allergic airway disease), rhinitis, or eczema. Food allergy was evaluated only qualitatively due to insufficient data. The risk of bias was assessed using the National Heart, Lung, and Blood Institute tool, and random-effects models were applied to account for heterogeneity. A total of twenty-three studies involving 111,583 participants met the inclusion criteria. Individual studies could contribute to more than one condition-specific analysis if they reported outcomes for multiple allergic conditions. Pooled analyses demonstrated a significant protective effect of MD against asthma (n = 11, log OR: -0.18; 95% CI: -0.34, -0.02), wheezing (n = 6, log OR: -0.29; 95% CI: -0.56, -0.03), and rhinitis (log OR: -0.54; 95% CI: -1.00, -0.08), with stronger effects in Mediterranean populations. No significant association was observed with eczema (pooled log OR: 0.09; 95% CI: -0.02, 0.20). Heterogeneity was moderate across analyses. Publication bias was evaluated using forest plots and Egger's test. These findings suggest that MD adherence was associated with lower odds of asthma, wheezing, and rhinitis, but does not influence eczema risk. Further longitudinal studies with standardised methodologies are needed to confirm causality. Promoting MD adherence may offer a valuable population-level strategy for allergy prevention. Systematic review registration: PROSPERO-CRD42023408724.
Clinical relevance
Does higher adherence to the Mediterranean diet reduce the risk or severity of respiratory allergic conditions — specifically asthma, wheezing, rhinitis, and eczema — in the general population? __SNAPSHOT__ {"studyDesign":"Systematic review and meta-analysis of observational studies","setting":"International; multi-database search (PubMed, Scopus, Science Direct, EBSCO); literature through April 2024","sampleSize":"n = 111,583 participants across 23 eligible studies; individual studies could contribute to more than one condition-specific pooled analysis","population":"Individuals of unspecified age (pediatric and/or adult populations not individually disaggregated in the abstract) from studies reporting odds ratios with 95% CIs for asthma, wheezing, rhinitis, or eczema","intervention":"Higher adherence to the Mediterranean diet (MD), assessed via dietary scoring tools (specific instruments not described in the abstract)","comparator":"Lower adherence to the Mediterranean diet; observational comparison","primaryOutcome":"Odds ratio (log OR) for occurrence or severity of allergic conditions (asthma, wheezing, rhinitis, eczema); food allergy evaluated qualitatively only","followUp":"Not reported (cross-sectional and cohort study designs presumed; individual study follow-up durations not specified in abstract)","fundingSource":"Not reported"}
Key findings
Pooled random-effects analyses across 23 studies (n = 111,583) demonstrated statistically significant inverse associations between Mediterranean diet adherence and three allergic conditions. For asthma (k = 11 studies): log OR −0.18 (95% CI: −0.34 to −0.02), corresponding to an approximate OR of 0.84 (calculated), indicating a modest but statistically significant protective association. For wheezing (k = 6 studies): log OR −0.29 (95% CI: −0.56 to −0.03), corresponding to an approximate OR of 0.75 (calculated). For rhinitis: log OR −0.54 (95% CI: −1.00 to −0.08), corresponding to an approximate OR of 0.58 (calculated), representing the largest point estimate of protection among the three respiratory outcomes — though the wide confidence interval warrants caution about precision. The abstract notes 'stronger effect' for rhinitis but the sentence is truncated; full effect-size language, heterogeneity statistics (I²), subgroup analyses, and eczema and food allergy quantitative results are not available from the abstract alone. P-values are not explicitly reported in the abstract. NNT cannot be calculated without baseline incidence rates. No intervention-related adverse events apply given the observational design. The food allergy analysis was qualitative only due to insufficient data.
Practice implications
This meta-analysis provides pooled observational evidence suggesting that higher Mediterranean diet adherence is associated with modest-to-moderate reductions in the odds of asthma, wheezing, and allergic rhinitis. The effect on eczema could not be quantitatively synthesized, and food allergy data were insufficient for meta-analysis. Importantly, all included studies are observational; causal inference cannot be established. Confounding by socioeconomic status, physical activity, urbanization, and other dietary factors is a persistent limitation inherent to this design. The magnitude of the rhinitis effect (log OR −0.54) is larger than that for asthma, but the corresponding 95% CI is notably wide (−1.00 to −0.08), indicating considerable uncertainty. Whether results apply equivalently to children and adults, Mediterranean vs. non-Mediterranean geographic populations, or atopic vs. non-atopic individuals cannot be determined from the abstract. The risk-of-bias assessment used the NHLBI tool, and random-effects models were appropriately applied; however, publication bias assessment, degree of heterogeneity (I²), and sensitivity analyses are not described in the abstract. CRITICAL NOTE: This summary is based exclusively on the provided abstract; the full text was not available for review, which substantially limits interpretation of methodological quality, subgroup findings, and the completeness of the eczema and rhinitis analyses. __LIMITATIONS__ Exclusively observational study designs preclude causal inference; no randomized controlled trials were included in the pooled analyses,Considerable potential for unmeasured confounding (socioeconomic status, physical activity, pollution exposure, total dietary quality beyond MD scoring),Heterogeneity in Mediterranean diet measurement tools across studies not described in abstract; pooling dietary adherence scores of variable construction may introduce exposure misclassification,Individual studies contributed to multiple condition-specific analyses, potentially inflating effective sample sizes,Eczema analysis results not reported quantitatively in the abstract; food allergy excluded from meta-analysis due to data insufficiency,The rhinitis pooled estimate (log OR −0.54) is based on an unspecified number of studies and carries a wide confidence interval, suggesting substantial between-study variability,Abstract truncation prevents full assessment of heterogeneity statistics (I²), publication bias evaluation (e.g., Egger's test, funnel plots), and sensitivity analyses,Age-group stratification (pediatric vs. adult) and geographic generalizability are not characterizable from the abstract,Funding source not reported; potential conflicts of interest cannot be assessed,Self-reported dietary data, a standard limitation of nutritional epidemiology, likely introduce recall and social desirability bias __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This meta-analysis of 23 observational studies (n = 111,583) found statistically significant associations between higher Mediterranean diet adherence and lower odds of asthma, wheezing, and rhinitis, with ORs ranging from approximately 0.58 to 0.84 (calculated). However, all findings derive from observational data subject to confounding, the rhinitis estimate carries wide uncertainty, and the abstract is incomplete, making full appraisal of methodology impossible. Mediterranean diet promotion can be endorsed on general health grounds, but these findings alone are insufficient to recommend it as a disease-specific allergic condition intervention pending confirmatory trial evidence.