Investigating the association between night eating symptoms and chronotype: the mediating role of depressive symptoms in a sample of Italian university students

Circadian rhythms significantly impact our sleep–wake cycle, wakefulness, and peak performance times [1]. Chronotypes refer to an individual's preference for the timing of their sleep–wake cycle and are part of their circadian rhythmicity [2]. They can be categorized into three types—morning, intermediate, and evening—reflecting an individual's activity and sleep patterns from early morning to late afternoon [3].

People with a morning chronotype tend to have an earlier sleep–wake cycle, and their mental and physical performance peaks in the morning [4]. On the other hand, those with an evening chronotype prefer to go to bed later and wake up later in the day [5]. Chronotypes are influenced by age, with a shift towards being an evening person in early adolescence and a constant transition to becoming a morning person as one ages [6]. Adolescents tend to have a delayed sleep and activity pattern, so it may be expected that a more significant number of young adults will report evening-type preferences than morning-type preferences [7]. In a study on a large 2135 Spanish university student sample, 16% were classified as morning, 60% as intermediate and 24% as evening types [8]. Riccobono et al. [9] in research regarding 1136 students at the L’Aquila University, Italy, reported a percentage of around 15.3% for Morning Type, 64.3% for Intermediate and 20.4% for Evening Type.

Recent studies have identified a strong link between an individual's chronotype and their mental health. The relationship between chronotype and emotional regulation processes has recently been investigated [1]. Watts and Norbury's study [10], found that expressive suppression was positively associated with eveningness, while morningness was positively associated with cognitive reappraisal strategies. Specifically, the evening chronotype has been associated with an increased risk of depressive disorders, while the morning chronotype is considered protective against such disorders [2]. Longitudinal studies have also shown that depression in adolescents can lead to a greater preference for staying up late, and the eveningness dimension has been linked to the later development of depression, highlighting a robust bidirectional relationship [11].

Individuals with an evening chronotype are more likely to experience circadian disturbances and changes in their eating behaviors [12]. This can affect their circadian preference, making them more prone to eating disorders than healthy individuals [13]. The food intake for humans occurs during the active phase, allowing for the replenishment of energetic reserves [14]. Conversely, the depletion of energy stores and the fasting period occurs during the non-active phase, which includes sleep [15]. This cycle is one of the strongest zeitgebers, in synchronizing circadian rhythms in peripheral tissues [16]. Thus, it may be one of the main issues in individuals with a disturbed circadian pattern, particularly in subjects that could suffer from night eating, like night-time workers [17].

Studies have shown that there is a bidirectional relationship between chronotypes and eating disorders, with changes in eating behaviors impacting an individual's circadian preference [18]. Night eating behavior has been closely linked to a delayed sleep phase and directly affects differences in chronotype [19]. Although the existing literature does not agree on the relationship between night eating behaviors and chronotypes, robust findings suggest a significant association between night eating behaviors and evening chronotypes [9, 20–22]. Additionally, night eating behavior has been associated with depressive symptoms in women [23] and young adults [24]. Interestingly, an association was found between levels of depression and episodes of night eating [25]. Night eating [26, 27], along with evening hyperphagia (consuming more than 25% of total calorie intake after the evening meal) [28] and loss of appetite in the morning are the core symptoms of Night Eating Syndrome (NES). This disorder has been recently recognized as a distinct disease in DSM-5 and is categorized under 'Other Specified Feeding or Eating Disorder' [29]. The prevalence of NES is 1.5% in the general population of the United States [30] and 8.2% among university students [31]. Individuals diagnosed with depression or depressive symptoms, particularly students [31], are at a significantly higher risk of experiencing NES [32, 33]. Several studies [34–36] have suggested a link between NES and depressive symptoms. Moreover, more than 50% of NES patients were found to be comorbid with major depressive disorder throughout their lifetime [37]. Indeed, NES frequently exhibit depressive symptoms that worsen in the evening hours [34–36]. Moreover, NES has also been associated with higher body mass index (BMI); however, literature concerning the association between night eating and BMI produced mixed findings, with emotional eating and age as potential moderators of this relationship [38].

Different studies [9, 19, 22] have pointed out that individuals with NES score lower on the MEQ, indicating an inclination towards an evening chronotype. Conversely, one recent study has proposed an association between the morningness dimension and NES [39] in a population of Greek non-clinical adults. Some studies [28, 34, 40] have also hypothesized that NES subjects present a circadian delay exclusively in their food intake, with unaltered circadian rhythms in global functioning. Various studies also identified a close relationship within the clinical population between the eveningness dimension and both NES and binge eating disorder [41], as well as between NES and both evening type and bipolar disorder [42–44]. A study has also established a correlation between evening chronotype, NES, and depressive symptoms in young adults [22]. Moreover, the efficacy of Bright Light Therapy (BLT) in treating night eating behavior and improving mood and sleep quality suggests the need for further investigations into the relationship between NES, mood, and circadian rhythms [45, 46]. Chronotype-related differences in eating patterns have been studied, but research on the connection between chronotypes and specific eating disorders is limited [47]. The evening chronotype was associated with food addiction in a cross-sectional survey of university students [48]. Interestingly, NES was found to be associated with food addiction more strongly in an adult community sample [49].

A large-scale study in Finland [50] investigated the relationship between chronotype, depressive symptoms, and emotional eating behavior, confirming a negative correlation between morning preference and both depression and emotional eating. The study conducted by Kandeger and colleagues (2018) found that night eating symptoms directly affect chronotype differences and insomnia severity and indirectly affect disordered eating attitudes by increasing insomnia scores [19]. Another study found that the chronotype of patients with bipolar disorder had both a direct effect and an indirect effect on their night eating symptoms [43]. The indirect effect was partially mediated by the quality of sleep. Additionally, the study showed that seasonality directly impacts night eating symptoms in the same patients.

To date, no in-depth research has explored the connection between an individual's chronotype, night eating, and depressive symptoms. Understanding the underlying mechanisms of these potential links is crucial to treating and preventing night eating effectively. The current study aims to clarify the relationship between night eating symptoms and chronotype by examining the role of depressive symptoms in a sample of university students. Specifically, we hypothesized that the dimension of eveningness could be related to night eating symptoms through the mediation role of depressive symptoms.

All participants were invited to complete a sociodemographic survey, including health-related information such as weight and height. Moreover, participants completed a battery consisting of three self-report questionnaires: the Night Eating Questionnaire (NEQ), the Morningness–Eveningness Questionnaire (MEQ), and the Beck Depression Inventory (BDI).

Descriptive statistics were employed to examine the sociodemographic characteristics of the sample group together with frequencies and percentages. The data are presented as mean ± SD (standard deviation) for continuous variables and percent frequency for categorical variables. One-way analysis of variance was used to compare the MEQ, BDI, NEQ, and body mass index (BMI) scores among the chronotypes. To assess the relationship among night eating symptoms (NEQ), chronotype (MEQ), body mass index (BMI), and depressive symptoms (BDI), correlation coefficients and their significance were computed using Pearson (r) correlation analysis. One-tailed p-values less than 0.01 were considered statistically significant. A significance threshold of p < 0.01 was adopted, as stricter criteria are typically recommended in exploratory studies seeking to identify potential associations or effects [54].

Mediation analyses were conducted using the SPSS Macro PROCESS (version 3.3). Specifically, we aimed to examine the indirect relationship between chronotype differences and night eating symptoms, with a specific emphasis on the potential influence of depressive symptoms. While mediation analyses can suggest causal pathways, the limitations of the atemporal cross-sectional design used in this study prevent us from determining definitive causal relationships; rather, these analyses explore the interrelationships among multiple variables.

All the statistical analyses were performed with IBM SPSS Statistics for Windows, Version 20.0. (IBM Corp, Armonk, NY, USA).

MEQ (R² = 0.376, F (2,900) = 96.19, P > 0001) had a statistically significant negative direct effect on both BDI (β = − 0.238, P < 0.001) and NEQ (β = − 0.371; P-value < 0.05) variables.

In this study, we evaluated the role of depressive symptoms in the relationship between chronotype and night eating symptoms in a sample of university students.

The general population prevalence reported for NES is 1.5% in the United States [25], 1.1% in Germany [32], 1.5% [49] in Japan, and 0.9% in Australia [26]. Unfortunately, no data regarding the general prevalence among the Italian general population are currently available, representing a gap in the literature.

The prevalence among university students is generally higher compared to the general population [50]. Our results revealed a prevalence rate of 3.6% for NES, which is consistent with the rates reported in other studies in the USA: respectively, 4% [14] and 5.7% [47], and in China 5.4% [48] among groups of college students.

Indeed, prolonged use of computers, tablets, and screens, as observed in academics [55], could lead to circadian lag and increased development of night eating behaviors among college students [56]. Interestingly, a recent study [39] found a higher prevalence of NES (8.1%) in a sample of non-clinical Greek adults, shedding light on the possible impact of latitude, culture, occupation and working hours on the prevalence of NES.

Our study revealed no correlation between night eating symptoms and BMI, suggesting, in line with the literature, that this association may be more evident in clinical samples [9, 20, 57]. Moreover, BMI was correlated with NES assessed with the NEQ in a sample of college students [57]. Furthermore, a previous study [58] proposed that age may mediate the relationship between NES and BMI, indicating a strong association between NES and BMI in subjects aged 55–60, with no correlation in younger subjects. Our results are consistent with this hypothesis.

In line with the current literature, our correlational analysis revealed a significant relationship between night eating symptoms and depressive symptoms [23, 24]. The relationship between depressed mood and night eating behavior has been a topic of debate, but it has been consistently identified in most studies [27, 28, 59]. Numerous studies [36, 60] have found that a high percentage of individuals with NES meet the criteria for major depressive disorder and have suggested that depression, male gender, and a BMI above 25 could be considered risk factors for NES [32]. Although the role of serotonin is still debated in depression [61], this neurotransmitter may be involved in the pathophysiology of night eating. This hypothesis may be supported by single-photon emission computed tomography, which has revealed a significant increase in serotonin transporters in the midbrain of individuals with NES [60]. Increased serotonin transporter levels could contribute to diminished postsynaptic serotonin transmission, potentially impairing circadian rhythms and satiety [62]. These findings may also help explain the strong connection between night eating, depressive symptoms, and circadian rhythm, and may suggest that enhancing serotonin function can effectively treat night eating. [62].

Further, our results provided insights into the relationship between night eating and evening chronotype. In the context of the ongoing literature debate about the role of the eveningness dimension in night eating, we have confirmed the robust relationship between NES and evening chronotype among university students [9, 20]. The current results suggest that individuals with NES might present a circadian delay in food intake and general functioning, highlighting the importance of investigating whether night eating symptoms directly influence chronotype [19]. Researchers have hypothesized that the relationship between night eating and circadian rhythm should be assessed in both directions, considering various factors such as artificial light exposure, melatonin, temperature, and digital utilities that may impact this relationship [12, 63]. Further research is needed to explore this relationship and identify potential mechanisms that underlie it.

Moreover, our study shed light on the critical role of depressive symptoms in the relationship between chronotype and night eating. Specifically, our results in a sample of university students show a pathway from chronotype to night eating, influenced by depressive symptoms. There are several possible explanations for this finding. Night eating symptoms in university students with an evening chronotype may function as a coping strategy for depressive symptoms linked to higher stress levels, as seen in other eating disorders [64]. Otherwise, night eating may be a consequence of depressive symptoms among the many possible manifestations [24].Furthermore, the misalignment of the central and peripheral circadian clocks associated with the evening chronotype, in addition to changes in the HPA axis and increased levels of cortisol, could provide an explanation for these findings [64]. The dysregulation of cortisol peak is a shared characteristic of evening chronotypes [65], depression [66], and NES [67]. This common biological profile could explain the effectiveness of selective serotonin reuptake inhibitors (SSRIs) in treating night eating. SSRIs may work by lowering cortisol levels [68], realigning evening misalignment of the circadian rhythm, and alleviating depressive symptoms, which could contribute to night eating. On the other hand, the mediation of depressive symptoms is partial and not complete. Food addiction has been correlated with the severity of night eating, the dimension of eveningness, and depression [48, 49]. It would be interesting to investigate whether depressive symptoms in university students could mediate the relationship between food addiction and chronotype, also considering the relationship with the severity of night eating [48, 49]. Future studies would be interesting to investigate whether other variables mediate the relationship between night eating symptoms and chronotype, such as food addiction, emotional regulation or insomnia and sleep quality [11, 19, 48, 49]. These findings enrich current knowledge on the impact of depressive symptoms on night eating behaviors [23–25], with important implications for chronotherapeutic approaches such as BLT in treating night eating symptoms [45, 46]. BLT can regulate the circadian rhythm and alleviate symptoms of disorders caused by circadian shifts or disruption while also addressing mood symptoms [69]. Therefore, our results emphasize the importance of increasing the utilization of chronotherapeutic approaches as a cost-effective and well-tolerated therapy for night eating symptoms, as suggested by other researchers [70].

Overall, these results suggest that an increase in depressive symptoms may be a critical factor impacting night eating behaviors in college students with an evening chronotype. Implementing chronotherapeutic interventions like BLT can help protect such students from developing depressive symptoms and night eating. Further research is needed to understand the underlying mechanisms behind this relationship and identify the most effective treatment options for night eating symptoms and NES in different populations.

Our study has some limitations that need to be considered. Firstly, it was conducted solely on university students, which might make it difficult to generalize the findings to a larger population. Additionally, we did not conduct psychiatric interviews with the participants, and the entire dataset was based on self-reported data, which could have potential biases. However, the validity of self-reported data for medical conditions has been demonstrated in several studies [71, 72], and they are commonly used in screening and surveillance programs [73, 74].

Despite some biases reported in the self-reporting of height and weight, particularly at extreme values, estimated anthropometric measurements used to calculate BMI are generally accepted and considered sufficiently reliable [75]. Further limitations include the sample having a higher prevalence of women, who are particularly vulnerable to nocturnal eating disorders and depression [23]. The restricted list of variables and the non-inclusion of other variables that could have served as mediating or moderating factors constitute another limitation.

In this context, future clinical studies should aim to validate our findings to further clarify the relationship between chronotype differences and night eating symptoms. Furthermore, it is crucial for these studies to investigate additional relevant variables, such as emotional regulation, anxiety, and personality characteristics, to assess their potential impact on night eating behaviors. Lastly, the cross-sectional study design may be considered a limitation. More detailed findings can be obtained from longitudinal and prospective studies.

The existing literature regarding chronotypes, NES and depression has been mainly conducted on university students and adolescents [16, 17]. Morning preference has a negative correlation with both depression and emotional eating in the general population [42]. Night eating symptoms have a direct effect on the chronotype differences [13] among university students, and the chronotype of patients with bipolar disorder had both a direct effect and an indirect effect on their night eating symptoms [37].

This study aims to investigate the relationship between night eating symptoms and chronotypes by examining the role of depressive symptoms in university students. Given its partial mediating role, increased depressive symptoms, together with other variables may possibly explain the relation between evening chronotype and night eating in university students.