Sleep Characteristics and Insomnia Severity in Relation to Mediterranean Lifestyle Adherence and Psychosocial Wellbeing: Findings from the MEDIET4ALL International Survey

Sleep is a multidimensional health domain influenced by behavioural, psychological, and lifestyle factors. However, multinational evidence integrating insomnia severity and multiple sleep outcomes within the Mediterranean lifestyle framework remains limited. This study examined correlates of insomnia severity and key sleep outcomes in adults from Mediterranean and neighbouring countries participating in the MEDIET4ALL survey. Data were collected from 4010 adults (59.5% female) across 10 countries using a standardized multilingual e-survey. Insomnia severity was assessed as primary outcome using the Insomnia Severity Index (ISI), while sleep characteristics were assessed using sleep duration, sleep latency, sleep efficiency, and subjective sleep quality. Regression analyses examined sociodemographic, health-related, Mediterranean dietary, movement-related, psychological, and social correlates. Exploratory statistical indirect association analyses involving life satisfaction were also conducted. Insomnia severity showed the highest explained variance among sleep outcomes (adjusted R2 ≈ 0.29). Higher insomnia severity was associated with female sex, higher body mass index, and greater depression, anxiety, and stress (β ≈ 0.15–0.17), whereas lower insomnia severity was associated with older age, better self-reported health status, higher life satisfaction, and greater adherence to Mediterranean dietary consumption patterns (β ≈ −0.04 to −0.11). Models for secondary sleep outcomes explained more modest variance and should be interpreted as exploratory. Across these outcomes, psychological well-being and distress showed the most consistent associations, while Mediterranean dietary dimensions and social participation showed smaller and outcome-specific associations. Exploratory indirect association analyses showed small but statistically significant indirect associations involving life satisfaction between Mediterranean dietary dimensions, social participation, and selected sleep outcomes, particularly sleep quality and insomnia severity. The findings confirm and contextualize established associations between sleep, psychological well-being, distress, Mediterranean lifestyle-related behaviours, and regional context within a large multinational sample. Psychological well-being and distress emerged as the most consistent correlates. Insomnia severity was the most robustly explained sleep outcome, whereas secondary sleep dimensions reflected more modest exploratory correlational profiles.