The influence of physical activity, social relationships, and diet intake on depression: a case-series study

Introduction: This paper aims to investigate the three areas [diet, physical activity (PA), and social relationship] and their relationship with depressive disorders in the North African population. Study design: This is an observational cross-sectional study of 654 participants residing in the urban commune of Fez (n=326) and the rural commune of Loulja (n=328) in the province of Taounate. Participants were categorized into two groups: G1 without a current depressive episode and G2 with a current depressive episode. Risk factors, including locality, gender, marital status, age, parental status, employment status, tobacco use, alcohol consumption, social habits, and dietary patterns, were assessed. A multinomial probit model in Stata software was used to identify factors associated with depression occurrence in the population. Results: A total of 94.52% of the participants who engaged in PA did not experience a depressive episode (P=0.001). Additionally, 45.39% of the participants in our series were on a processed diet and presented with a depressive disorder (P=0.0001), the social contact (time spent with friends >1.5 h) remained strongly associated with reduced depressive symptoms when comparing the two groups (P=0.001). The results showed that being rural, a smoker, an alcohol user, and having no spouse significantly increased depression in participants. The coefficient of age was negatively related to the probability of the occurrence of age-related depression; however, this factor was not significant in the model. Thus, having a spouse and/or children and spending time with friends on a healthy diet significantly decreased depression in our population. Discussion: The converging evidence suggests that physical exercise, a stable social relationship, a healthy diet, and the use of PA can alleviate depression symptoms, but limited understanding and few studies have attempted to characterize or identify the neural mechanisms of these effects. Conclusion: Nonpharmaceutical interventions such as PA and dietary changes have proven to be effective treatments for depression, while maintaining positive social relationships can act as a protective factor, serving a prophylactic role in the prevention of depression.


Introduction
Major depressive disorder is a serious mental disorder that has a significant impact on an individual's overall well-being. It is a leading cause of disability worldwide, with ∼350 million people currently affected by this condition [1] . While the underlying causes of major depressive disorder are not well understood, recent research has focused on the role of psychological stress in its development [1][2][3] .
Several factors have been identified as playing a crucial role in the development of depressive disorders, including diet, social relationships, and physical activity (PA). The relationship between diet, mood disorders, and obesity is complex and bidirectional [4][5][6] . Meanwhile, evidence suggests that physical exercise and stable social relationships can help alleviate symptoms of depression. However, few studies have attempted to characterize or identify the neural mechanisms behind these effects [2,[7][8][9] .
The purpose of this paper is to investigate the possible role of diet, PA, and social relationships in the occurrence of depressive disorder in the population. Specifically, we aim to answer the HIGHLIGHTS • Physical activity and social relationships are nonpharmaceutical treatments of choice for depression. • There is a significant inverse association between diet quality and depression and anxiety. • Being rural, a smoker, an alcohol user, and having no spouse significantly increased depression.
following question: Do these three factors play a role in the development of this disorder? This case series has been reported in accordance with the PROCESS (Preferred Reporting Of CasE Series in Surgery) criteria [10] .

Study design
The study design used in this research was a cross-sectional study. Data were collected at a single time point, and no follow-up was conducted.

Study population
The study population comprised individuals from the North African population. A total of 654 participants were enrolled, with 326 residing in the urban commune of Fez and 328 in the rural commune of Loulja in the province of Taounate.

Sampling technique
A nonprobability sampling technique, specifically a convenience sampling method, was used to select participants for the study. Participants were recruited from healthcare centers in the two communes.

Inclusion criteria
To be eligible for the study, participants had to be aged 15 years and above and provide informed consent to participate in the study.

Data collection
The study collected data using a structured questionnaire administered by trained researchers to collect information on demographics, PA, diet, social relationships, and depressive symptoms. The Mini test was used to assess depression, while PA was assessed using the IPAQ (International Physical Activity Questionnaire). Information on age, gender, socioeconomic status, meal pattern, meal composition, etc., was obtained, and a short parental questionnaire was distributed to assess individual socioeconomic status factors. Written informed consent was obtained from the participant's parents.

Data analysis
The data collected were analyzed using the Stata software. Categorical data were summarized as frequencies and crosstabulations, while continuous variables were summarized as mean and variation. The χ 2 significance test was used to compare groups, with a two-sided P value of 0.05. A multinomial probit model was employed to determine the causal relationship between the different factors influencing depression in the population. The variables examined included locality, gender, having a spouse, age, having children, working, tobacco smoker, tobacco exposurework, tobacco exposurehome, double tobacco exposure, alcohol consumption, time spent with friends, Mediterranean diet (MD), mixed diet, poor diet, and processed diet. To ensure a rigorous analysis, an exploitation sheet was used. The statistical significance was set at P less than 0.05.

Sociodemographic profile of the population
The characteristics of the individuals are divided into groups based on the presence or absence of current depressive disorder as well as epidemiological considerations which are presented in Table 1.
Females were the majority, accounting for 50.9% of the study population, while males accounted for 49.1%, resulting in a sex ratio of 0.96 (M/F) (Fig. 1).
The mean age of the patients was 42.57 17.44 years, with extremes ranging from 15 to 79 years.
The age group between 25 and 34 years is predominant, with a rate of 28%, followed by patients aged 35-49 years with 26.9%.
Half of the population surveyed (57.4%) reported being married, with a significant difference between the two groups (P < 0.036). The widowers seemed to present the most depressive episodes, 52.38% against 47.62%.
However, the exercise of professional activity was not related to the occurrence of depressive episodes in our population (P = 0.627).

Risk behaviors
The prevalence of depression appears to be higher in heavy smokers than in nonsmokers.
In our series, 54.3% of our patients who presented with a current depressive episode were smokers (P = 000.1).
Exposure to tobacco in the workplace was usually found; 44.25% of our candidates reported a current depressive episode. However, exposure at home was found in 58.16% of cases (P = 0.0001). In the case of dual exposure (at home and work), 65.5% of our participants had a depressive episode.
On the other hand, in the consumption of alcohol found in our population, depressive disorders were present at a rate of 71.43% in the habitual consumers of alcohol (P = 000.1) (Fig. 2).

Social relationships and depressive disorders
A better understanding of social contexts could help identify key components of social interactions that are more strongly associated with better mental health and reduced symptoms of anxiety and depression.
In our study, time spent with friends (duration > 1.5 h) and the presence of children and spouses were evaluated as protective factors against depression.
On the other hand, less than half (35%) of older adults with depression reported spending no more than 1.5 h with friends (P = 0.001).
In addition, the survey revealed that having a child was not statistically significant between the two groups (P = 0.284).
However, adults with spouses were not likely to experience depressive episodes in our population (P = 0.244).
Thus, individuals with all types of support (confidant, emotional, and instrumental) had a higher likelihood of consulting for their depressive symptoms than those with less support (Table 2).

PA and depressive disorders
This study examined cross-sectional associations between PA, mental health, and anxiety-depressive symptoms in the population of Fez-Loulja.
In all, 5.58% of the physically active participants had a depressive episode, compared to 27.71% of the nonphysically active participants who had a depressive episode.
PA volume was positively associated with mental health and inversely associated with depressive symptoms (P = 0.001).
After controlling for PA volume, active youth participating in team sports had better mental health than those participating in individual activity (Table 3).

Nutrition and depression
The dietary typologies identified according to the total score calculated for the two groups, G1 and G2, reveal that more than half (83.5%) of the study population on a MD did not experience a depressive episode, compared to only 16.4% of the participants who had a depressive episode.
Our investigation also shows that processed food is strongly related to the current depressive episode (P = 0.0001).
Regarding the two remaining diets, the mixed diet, which is composed of both Mediterranean foods and processed foods, and the poor diet, represented by a low MDS (Mediterranean Diet Score) without processed products, the results were statistically significant between the two groups.
For the food typologies studied in our series, the difference is very significant between the two groups (Table 4).  The multinomial probit model The multinomial probit regression model was used to examine the factors that influence the occurrence of depressive disorder in our population in the Fez-Meknès region. Table 5 represents the maximum likelihood estimates of the multinomial probit regression model. The table shows that the estimated log-likelihood is − 256.05861. Since the maximum likelihood estimates are between 0 and 1, the log-likelihood estimate is always negative. The χ 2 distribution statistic was 154.99 (degree of freedom was 14).
The positive sign of the coefficient of the variable means that by changing the variable by one unit, participants can be expected to be more likely to be in the top category. On the other hand, the negative sign of the coefficient of the variable means that by changing the variable by one unit, one can expect participants to be more likely to belong to the lower category.
The ordered probit regression revealed that being rural, a smoker, an alcohol user, and having no spouse significantly increased depression in participants.
The coefficient of age was negatively related to the probability of the occurrence of age-related depression; however, this factor was not significant in the model.
Thus, having a spouse and/or children and spending time with friends on a healthy diet significantly decreased depression in our population.

Depression and PA
Depression is the biggest factor affecting patients' quality of life [3] .
PA has been shown to improve patients' clinical status in areas such as fatigue, depressive symptoms, sleep disturbance, and quality of life [11] .
One of the mechanisms involved in the effect of exercise and depression is endorphins.
Endogenous endorphins are opioid polypeptides secreted primarily by the hypothalamic-pituitary axis during intense exercise, excitement, and pain, and their actions resemble those of opiates in their ability to produce analgesia and a sense of wellbeing [12] .
The opioid system plays a key role in mediating analgesia and social attachment and may also affect depression, given the link between beta-endorphins and depressive symptoms [13][14][15][16] .
In addition, the mechanisms by which exercise may improve depression remain unclear, primarily due to the methodological limitations of existing research [17] .
Numerous studies have shown that men and women with obesity have a 55% increased risk of developing depression, Table 3 The relationship between physical activity and current depressive episode     [18][19][20] . Specifically, aerobic exercise indicated a moderate clinical effect, while mixed and resistance exercise indicated large effect sizes. Furthermore, when compared to other established treatments (i.e. cognitive behavioral therapy and antidepressants), exercise appeared to produce the same results ( Table 6).
The effectiveness of PA, such as general exercise and balance training, decreases depressive symptoms. However, stretching and Tai Chi do not affect depressive symptoms but can improve physical function and quality of life in patients [21,25,27,28] .
Indeed, published evidence shows that exercise and PA interventions are generally successful in reducing symptoms of depression [25] .
In a recent study, the authors were able to demonstrate that patients with major depression receiving aerobic training at home or in a supervised group setting achieved reductions in depression compared to standard antidepressant medications (sertraline) and greater reductions in depression compared to placebo controls [7] .
Numerous studies have shown that people with the major depressive disorder who follow an aerobic exercise program are equally likely to go into remission [23,26] as those taking standard antidepressants (sertraline) or combined medication and exercise [21] .
PA is of increasing interest in the prevention of mental disorders in youth. Recent studies have shown a reduction in depressive symptoms with PA. Therefore, PA may be a potential target for the treatment and mitigation of negative symptoms such as depressive disorders [29][30][31][32][33] .
In our series, 94.52% of the participants who engaged in PA did not experience a depressive episode (P = 0.001). Our results were consistent with the literature; therefore, PA interventions may be a therapeutic target when treating depression.

Depression and nutrition
The multifactorial relationship between diet, mood disorders, and depression is bidirectional and complex [18] .
Based on the study by Gantenbein and Kanaka-Gantenbein [34] , it is established that a healthy diet, in terms of adherence to the MD, rich in fruits, vegetables, olive oil, herbs, and spices, and a high intake of fiber, can have a beneficial effect on mental health.
It has been described that the beneficial effects of the MD can be mainly attributed to its many components rich in antiinflammatory and antioxidant properties [35][36][37] .
In addition, the MD may contribute to improved reproductive health, modify the risk of neurodegenerative diseases and protect against depression and psychosocial maladjustment. The beneficial effects of the MD can be enhanced by increased PA as part of a healthy and balanced lifestyle [34] .
The great variety and diversity of bioactive compounds present in the various dietary interventions, as well as the pleiotropic properties of these compounds, make their effects and the study of these effects inherently complex [19] . This is further complicated by the lack of research that has studied the comparative effectiveness of a wide range of potentially therapeutic dietary interventions (e.g. MD, ketogenic diet, or caloric restriction), which differ considerably in their macronutrient and micronutrient composition (Table 7).
In this regard, many studies have concluded the relationship between increased potential diet and depression. Thus, significant differences have been recorded between diet and depression. The team of Sánchez-Villegas et al. [40] demonstrated that adherence to MD ensures an adequate intake of B vitamins and W-3 fatty acids [42] . A protective role on depression has been suggested for these two nutrients. Our results indicate that the diets intervene directly on the psychological state of the participants (in our framework: the expression of symptoms related to depression).
As a result, 45.39% of the participants in our series were on a processed diet and presented with a depressive disorder (P = 0.0001), which is in line with the results of the team of Akbaraly et al. [39] . The results suggest that a diet based on processed foods is a risk factor for depression.
However, 16.4% of participants on the MD had a depressive episode. Our data are consistent with the literature. This suggests that diet plays a central role in the body's antioxidant metabolism by reducing biological stress. Finally, intervention in the dietary axis appears beneficial in reducing negative symptoms related to depression. Burini et al. [21] 26 62.7-65.7 Aerobic training 50 min 3 times/week for 7 weeks BDI-II No significant change Lee et al. [22] 20 68.4-70.1 Dance exercise 30 min 5 times/week for 6 weeks BDI-II Positive effect on balance, activities of daily living, and depressive disorder status Tanaka et al. [23] 20 64.6-64.8 Aerobic training 60 min 3 times/week for 6 weeks HADS No depressive symptoms (HADS = 8 or higher) Dereli and Yaliman [24] 32 61.3-66.5 Stretching, relaxation exercises 45 min 3 times/week for 10 weeks BDI-II Improvement in BDI and activities of daily living Schmitz-Hübsch et al. [25] 56 63.8 Qi-Gong 60 min 8 weeks with a break of 8 weeks MADRS Depression and nonmotor symptoms decreased in the treatment group Khallaf and Fathy [26] 30 49-70 Aerobic training 6-20 min 6 weeks HDRS More efficacy in activities of daily living and depressive symptoms Cheon et al. [27] 23

Depression and social relationships
Social support may be particularly important in combating depression in systematically disadvantaged groups [43] . One reason given for this phenomenon is the strong social support provided by kinship networks. Support from family and friends had protective effects on depression risk; however, after mutual adjustment, only family support remained statistically significant (Table 8).
At higher levels of family support, foreign-born Mexicans and African Americans had a lower risk of depression than at low levels of family support [44] .
The risk of major depression in the past year was inversely associated with supportive relationships with spouses and significant others and directly associated with problems in those relationships (e.g. too many demands, criticism, tension, and disagreements) [50] .
History of major depression in one twin significantly predicted low parental and spousal support, as well as problems with relatives and friends, in his co-twin. The relationship between social support and depression in women is even more complex [50] .
In addition, Hefner and Eisenberg [47] showed that students with characteristics different from most other students, such as race or minority ethnicity, international status, and low socioeconomic status, were at greater risk of social isolation. For their part, students with lower quality social support, as measured by the multidimensional Perceived Social Support Scale, were more likely to experience mental health problems, including a six-fold increase in risk for depressive symptoms compared to students with high-quality social support. These findings may help healthcare administrators and providers more effectively identify the population of students at high risk for mental illness and develop effective interventions to address this important and growing public health problem [47] .
According to Stafford et al., positive and negative exchanges with partners and children were independently associated with depression, controlling for age, gender, wealth, and initial Table 7 The effect of diet intake on depression

Authors
Years Country Diet Study Results P Sánchez-Villegas et al. [40] 2009 Spain M C Greater adherence to the Mediterranean diet is associated with a reduced risk of self-reported depression (traditional) < 0.001 Okubu et al. [41] 2011 Japan J C No significant association 0.59 Mamplekou et al. [20] 2010 Mediterranean Islands M O No significant association NS Akbaraly et al. [39] 2009 England T C Increased consumption of processed foods is associated with an increased likelihood of depressive symptoms 0.001 Chatzi et al. [35] 2011 Greece O C No significant association 0.70 Nanri et al. [36] 2010 Japan J O Greater adherence to the Japanese diet is associated with a reduced risk of depressive symptoms < 0.001 Jacka et al. [37] 2011 Norway N O Greater adherence to the Norwegian diet is associated with a reduced risk of depressive symptoms in men 0.02 Parker et al. [42] 2010 South Korea L CT Greater adherence to a healthy diet is associated with a lower mean < 0.01 Aihara et al. [38] 2011 Japan E CT Greater adherence to eating balanced meals is associated with a reduced likelihood of depressive symptoms  Almeida et al. [44] 2009 The United States Friends C The effect of support from friends was protective against depression 0.76 (0.57-1.01) Barger et al. [45]  Eisenberg [47] 2009 The United States Friends M A six-fold increase in the risk of depressive symptoms in students with poor-quality social support and those with good-quality social support 0.77 (0.39-1.52) McKenzie et al. [48] 2013 The United States Friends C The association between social contact and depression was stronger for men than for women 0.37 (0.22-0.63) Stafford et al. [49] 2011 England Friends C Negative, but not positive, exchanges with other family members and with friends were associated with depression 0.98 (0.91-1.05)

Wade and
Kendler [50] 2000 The United States Friends/ family O The risk of major depression was inversely associated with supportive relationships with spouses and significant others and directly associated with problems in these relationships 0.96 (0.86-1.07 C, cohort; M, a meta-analysis; O, observational; OR, odds ratio.
depression. Negative, but not positive, exchanges with other family members and with friends were associated with depression. The association between depression and positive-negative exchanges was weaker for those over 70 than for those between 50 and 70 [49] . Negative and positive exchanges with partners and children appear to be equally important in the development of depression, but negative exchanges with family and friends contribute to depression, while positive exchanges do not [49] .
Our study concluded that social contact (time spent with friends > 1.5 h) remained strongly associated with reduced depressive symptoms when comparing the two groups (P = 0.001). However, digital social networks are one of the fastest growing industries, creating a new platform for establishing social contacts at a distance. It is important to explore how to maximize the potential of digital social networks to strengthen social ties while balancing their negative effects.

Limitations
The type, extent, and impact of measurement error, as well as interindividual variation, is an open area of research.

Conclusion
Exercise and diet are nonpharmaceutical treatments of choice for depression. The benefits of exercise and a balanced diet may also persist beyond the end of treatment, unlike antidepressant medications.
However, a good social relationship seems to be a protective factor and has a prophylactic role.
Future studies need to test whether the brain regions identified in this review may be neurobiological markers of depression that could serve as targets for exercise-based treatments for depression.

Ethical approval
Not applicable.

Consent
Not applicable.

Sources of funding
Not applicable.