Findings of the present population-based cross-sectional investigation revealed an interaction between higher adherence to the mMED DP and severe depression on the risk of participants' "low sleep quality". To our knowledge, this is the first effort to evaluate the interaction between priori DPs and PAs on human sleep indicators.
Impaired sleep is recognized as a critically important aspect of human lifestyle that has recently gained prominence in clinical investigations due to its related psychological and physiological complications (10, 48). There are convincing reports in relation to the bidirectional link between dietary eating components and sleep. For instance, the consumption of particular nutrients may stimulate a number of hormonal signaling pathways, resulting in sleep quality and duration alterations (49, 50). Conversely, it has been documented that unfavorable sleep quality together with impaired sleep duration can affect dietary eating behavior (36).
In total, the majority of studies in relation to DP assessment have focused on a) statistical techniques (posteriori DPs) and b) dietary quality score approaches (priori DPs), which are characteristically specified by simple interpretable dietary guidelines (51, 52). Over the past few decades, DASH and Mediterranean diet styles have become widely accepted a priori DPs as a result of their convincing proof of their health advantages (53, 54). According to earlier investigations, a positive association has been established between these popular healthy vegetable-rich DPs and suitable sleep quality (36, 55, 56). In 2017, an investigation on older adults showed that higher imitation to a Mediterranean DP was linked to greater sleep quality, coupled with a decreased likelihood of variations in sleep duration (37). Moreover, Godos et al. (56) described a higher sleep quality following a Mediterranean DP in Italian adults. Likewise, in 2020, Liang et al. (36) suggested the health advantages of the DASH DP in relation to sleep duration and quality. Earlier findings have shown that a diet with less intake of vegetables, fruits, and seafood and more consumption of processed foods and meals high in free sugar may be significantly linked to higher sleep disorders (18, 57). In general, the total dietary intake of protein, fiber, magnesium, and potassium is accepted as a number of well-known beneficial nutrients in both DASH and Mediterranean DPs, which have been assumed to impact sleep features (22, 56). It has been documented that DPs with higher consumption of dietary fiber, magnesium, and potassium may improve the quality of sleep (18, 36, 58). One cross-sectional investigation has indicated a direct association between the amount of dietary fiber intake and sleep quality indicators (59). Similarly, a positive relationship has been found regarding the dietary intake of magnesium and sleep duration in both young and older women (60). It appeared that magnesium may act as a regulatory factor in the circadian cycle. It may also promote sleep through the synthesis of melatonin (61, 62). In addition, the Mediterranean diet comprises seafood, nuts, and seeds, which can increase the availability of tryptophan and thus enhance serotonin synthesis as a promoter agent for sleep (63, 64).
On the other hand, mutual relations have been discovered between dietary eating, sleep features, and PAs (2, 65). In one study, the researchers observed higher symptoms of depression and anxiety in suboptimal sleepers (those sleeping less than 6 or 8.5 or more hours/night) compared to subjects reporting an average of 6 hours or less than 8.5 hours/night (66). Additionally, low quality of sleep has been documented in adolescents experiencing anxiety or depression (67). "As sleep can be both a precipitant and a consequence of mental health"(68), healthcare scientists have recently emphasized lifestyle modifications as a protective approach (69). Meanwhile, diet as a lifestyle behavior may have an impact on processes in the human brain that contribute to the development of PAs, particularly depression, such as synaptic plasticity, membrane fluidity, and neuroinflammation, as well as the regulation of neurotransmitter production (70). It has been established that a higher adherence to the Mediterranean DP is related to mental and psychological profile well-being (56). Previous studies have proposed several underlying mechanisms regarding the association between diet and psychological impairments. Given that inflammation and oxidative stress have been suggested to be potential factors in the development of depression and psychological stress, the high content of antioxidant agents and beneficial dietary fats such as omega-3 fatty acids or virgin olive oil in Mediterranean DP may support the useful effects of this DP (32). In addition, improvements in other possible risk factors, including insulin sensitivity, vascular inflammation, endothelial dysfunction, and metabolic syndrome, have been suggested through a high adherence to the Mediterranean DP, which in turn may diminish the risk of PAs (56, 71).
The strengths of the present investigation include the analysis of an extensive population, the benefit from validated metrics to evaluate the mMED diet score, psychological signs, and sleep parameters, and the adjustments for a broad spectrum of sociodemographic and clinical data. However, it is important to consider the main limitations of the investigation. The cross-sectional design of this project precludes the inference of causation and temporal effect. In addition, biases including measurement error, misclassification, recall, and social desirability are all possibilities when using FFQs.