Mediterranean diet and chronotype: Data from Italian adults and systematic review of observational studies

Scientific evidence suggests a relation between dietary factors and sleep. Several studies show that higher adherence to the Mediterranean diet is associated with better sleep quality, but the relation with chronotype has been only recently explored. The aim of this study was to better understand the relation between chronotype and Mediterranean diet adherence. For this purpose, an analysis of 1936 adults (age 18-90 y) living in Italy was performed to investigate the association between chronotype (assessed with a short form of the morningness-eveningness questionnaire) and adherence to the Mediterranean diet (assessed through a 110-item food frequency questionnaire and the Medi-Lite literature-based Mediterranean adherence score). A multivariate logistic regression analysis was conducted to calculate odds ratios (OR) and 95 % confidence intervals (CIs) describing the association between chronotypes and high adherence to the Mediterranean diet (>14 points). Moreover, a systematic review of other observational studies published so far was performed. Individuals reporting having intermediate (n = 614) and evening (n = 173) chronotypes were less likely to have high adherence to the Mediterranean diet compared to morning chronotype (OR = 0.28, 95 % CI: 0.18, 0.42 and OR = 0.08, 95 % CI: 0.03, 0.27, respectively). When the analysis was conducted in subgroups of age, the results were similar in mid-age (>50 y) participants (for intermediate and evening chronotypes, OR = 0.21, 95 % CI: 0.10, 0.43 and OR = 0.92, 95 % CI: 0.01, 0.69, respectively) while the association with high adherence to the Mediterranean diet of evening compared to morning chronotype lost significance in older (>60 y) participants (for intermediate and evening chronotypes, OR = 0.27, 95 % CI: 0.09, 0.82 and OR = 0.22, 95 % CI: 0.02, 1.92, respectively). Out of 10 studies (date range of publication 2020-2022) included in the systematic review, there was a general consistence of findings showing higher adherence to the Mediterranean diet among morning chronotypes, although few studies reported null results. In conclusion, current evidence suggests that an intermediate and evening chronotype could be associated with lower adherence to a Mediterranean diet, but the association could be modified by other factors when considering older individuals.