Association between dietary diversity, sedentary time outside of work and depressive symptoms among knowledge workers: a multi-center cross-sectional study

Knowledge workers are defined as people whose jobs consist primarily of creating and/or transforming knowledge into original products [1]. They implicitly select and weigh key factors in decision-making in their particular problem domain [2], and apply information and communication technology to exchange meaning [3]. This group is critical to currently service- and knowledge-based economy, in which innovation and creativity dominate [4]. With the rapid development of technology and society, the need for knowledge workers is increased [5]. However, because of the nature and characteristics of the work, this group of workers faces numerous health and psychological problems, such as depressive symptoms [1].

High levels of sedentary behavior have been identified as a risk factor for depressive symptoms and cardiometabolic health issues [6‐8]. According to our knowledge, because of the need to complete certain tasks, sedentary time at work is not entirely under an employee's control. Therefore, health workers need to focus their intervention programs on reducing the amount of sedentary time spent outside of work hours. Research indicated that sedentary time and dietary patterns positively influenced the association between obesity and psychopathological symptoms in overweight/obese subjects [9]. In addition, there is also a significant association between sedentary and unhealthy dietary behaviors and psychological health-related outcomes in high school students [10]. Studies also suggested that depressive symptoms are associated with a sedentary lifestyle and dietary patterns in different groups, such as medical students, women, and older adults [11‐13].

Dietary diversity has been considered an essential component of a healthy diet [14], a key indicator of high dietary quality in different populations [15, 16]. Dietary diversity score (DDS) is an a priori-defined dietary quality evaluation index[17]. United States Department of Agriculture’s (USDA) Dietary Guidelines and Food Guide Pyramid states that dietary diversity is one of the characteristics of a healthy diet [18]. The Chinese Dietary Guideline also indicates that people should consume as many kinds of food as possible [19]. Undernutrition and low-diversity diets may be risk factors for the occurrence or progression of mental disorders [20]. Globally, approximately 5% of excess mortality can be attributed to inadequate consumption of fruits and vegetables [21]. Consuming diverse vegetables contribute to reducing depressive symptoms [22]. diversity diet is a significant mediator between dietary quality and depression [23]. Balanced diet is important for people’s health, previous studies indicated that the low vitamin D levels are associated with a variety of diseases [24], different vitamin supplement usage may associate with the disease management [25, 26].

Knowledge workers need to continuously learn and compete to avoid becoming obsolete. As a result, they are at high risk for depression under chronic high stress [27]. Low-diversity diets and sedentary status are risk factors for depressive symptoms. The association between dietary diversity, sedentary and depressive symptoms was investigated in different populations, especially for adolescent. One study found that depressive symptoms in overweight and obese women from disadvantaged communities are associated with dietary intake but not physical activity [28]. A study found a connection between sedentary and dietary behaviors and depressive symptoms in adolescents [29]. Increased unhealthy dietary pattern scores and physical activity guideline attainment were associated with depressive symptoms in males, whereas screen time guideline attainment (sedentary) was associated with depressive symptoms in females [29].

However, the above studies were not performed using a large population, nor did the study groups include knowledge workers [30‐32]. There rarely studies have examined the association between dietary diversity or sedentary behavior outside of work and depressive symptoms among knowledge workers. Therefore, the purpose of this study was to (1) determine the dietary diversity score, sedentary time spent outside of work, and depression among a large population in China; (2) determine the association between the dietary diversity score and sedentary time spent outside of work and depression; and (3) detect other influencing factors of depression in this group for further systematic review.

The study provides preliminary evidence of Chinese knowledge workers’ dietary diversity, sedentary time spent outside of work, depressive symptoms. We also explored the association between dietary diversity or sedentary time spent outside of work and depressive symptoms. In addition, gender, age, marital status, BMI, physical activity, eating habits and their association with depressive symptoms were investigated among knowledge workers. We found that a lower DDS score and greater sedentary time spent outside of work were significantly related to knowledge workers’ depressive symptoms. It was also surprising that 31.5% of participants reported depressive symptoms, which was marginally lower than the results reported in previous studies in Tehran (62.1%) and Korea (38.3%) [41, 42]. However, the sample sizes of those studies were smaller and limited to office workers. While 31.5% may not be a large percentage, because of the large sample size of this study, this population is too large to be ignored.

We found among those reporting diets in the DDS-1 and DDS-2 groups, the percentage of depressive symptoms was higher than in the non-depressed group, while the DDS-3 was inverse. An increase in dietary variety may reverse the percentage of depressive symptoms among knowledge workers. Besides, the DDS-3 degree is a protection factor against depressive symptoms in knowledge workers, and DDS is a negative association with depressive symptoms, which are similar to previous studies [43, 44]. Low DDS is a risk factor for depressive symptoms [45] and is inversely correlated with depressive symptoms [43]. The relationship between depression symptoms and single nutrients and foods, such as vitamins, folic acid and fish, is inconsistent [46]. Many nutrients are highly interrelated, and some may also influence the intestinal absorption of other nutrients [47]. A longitudinal study reported positive effects of greater food group diversity and maternal depressive symptoms [48]. Among adolescents, the proportion of moderate to severe and major depressive symptoms increased slightly as the DDS score decreased [49]. Dietary diversity in general, and diversity in certain food groups in particular, can reduce the risk of metabolism-related outcomes by improving the diversity of the gut microbiome [50]. which subsequently improves health outcomes and immune function[51]. The results of this study affirmed the above studies. However, most of the previous studies mainly concentrated on women or adolescents. Knowledge workers were ignored, which indicates that further research is needed among this group.

Regarding eating habits, knowledge workers who did not eat three meals regularly had an increased risk of depressive symptoms compared to those who ate three meals regularly. A regular diet is a protective factor against chronic stress, and most people with irregular diets have inadequate nutritional intake, especially folic acid, zinc and magnesium intake, which are beneficial for maintaining neurological function [52]. In addition, the hypothalamus is the main central structure regulating appetite and emotional responses; it is involved in the regulation of glucose metabolism while also regulating stress responses [53]. Therefore, dietary factors are closely related to the occurrence of depressive symptoms. Compared with those who overate, knowledge workers who never overate showed a lower risk of depressive symptoms. Hanna also indicated that emotional overeating was significantly associated with eating disorder characteristics and depressive symptoms [54].

Consuming sugary drinks daily was a predictor of having higher depressive symptomatology [55]. Sugar has been shown to have a very negative effect on brain proteins, mainly on neutrophic proteins, which are known to play a role in depressive symptoms because they protect the brain from oxidative stress and promote the growth of new brain cells [56]. Knowledge workers who smoked and consumed alcohol had a lower risk of depressive symptoms in our study. Lee et al. investigated the triple trajectories of alcohol use, tobacco use, and depressive symptoms among adults [57]. Two trajectories were presented: (1) low tobacco use, moderate alcohol use, and low depressive symptoms and (2) low alcohol use, no tobacco use, and high depressive symptoms. Moderate smoking and alcohol consumption may at some point alleviate depressive symptoms among knowledge workers.

Reducing sedentary time and increasing physical activity may ease depressive symptoms in different populations ranging from adolescents to middle-aged women to older adults [58‐60]. Our study also showed similar results: the percentage of depressive symptoms was higher than non-depressive symptoms with the gradual increase in sedentary time spent outside of work. Physical activity can reduce the risk of depressive symptoms among knowledge workers. Transient mood disorders caused by sedentary activity may interact with acute stress to strengthen the pro-inflammatory response [61]. Meanwhile, Passive sedentary activity replaces physical activity and may result in social isolation, which is associated with depression [62]. Sedentary behavior is one of the main causes of depressive symptoms in elderly patients with hypertension [63]. Meanwhile, Raudsepp & Vink suggested that early depressive symptoms also predict later sedentary behavior [64]. Knowledge workers spend most of their workday sitting; they sit up to 82% of their work time [65]. Accordingly, this increasingly sedentary behavior has become a major public health risk [66]. Previous studies have explored the factors influencing and barriers to changing the amount of sedentary time knowledge workers engaged in each day [30, 31]. Moreover, numerous intervention programs and treatments have attempted to reduce sedentary behavior and increase physical activity levels among knowledge workers [32, 67, 68]. A 22-month period longitudinal study reported that an increase in sedentary behaviors was inversely associated with a change in physical activity [69]. Physical activity intervention also reduced total sedentary time[70]. We particularly investigated the amount of sedentary time spent outside of work rather than sedentary time spent during the workday among knowledge workers. As we understood, this study is the first to explore the amount of sedentary time spent outside of work in a large population of knowledge workers. Programs and mechanisms targeting sedentary time spent outside of work merit further research.

Furthermore, compared with males, females knowledge workers showed a higher risk of depressive symptoms, which is similar to China Mental Health Survey [71], indicated that female patients accounted for more than 60% of the total number of depression patients. In addition, female patients also have a higher willingness to share and actively seek treatment through friends and relatives, patient communities, and various social channels than male patients [71]. It is possible that even though there were fewer female participants in this study, more women than men reported depressive symptoms. Older participants had a lower risk of depressive symptoms in this study, and Ogasawara et al. also indicated a significant relationship between depressive symptoms onset and younger age [72]. In this study, marriage was a protective factor for depressive symptoms. The contribution of marriage to mental health was greatest if both married partners were employed [73].

Our study was the first to concentrate on the effect of dietary diversity and sedentary time spent outside of work on depressive symptoms among knowledge workers. We concluded that more sedentary time spent outside of work and lower levels of dietary diversity are risk factors for depressive symptoms. In addition, eating irregularly and overeating are also major risk factors for knowledge workers’ depressive symptoms. Future studies should apply objective indicators to explore the influencing factors contributing to depressive symptoms in this group. Furthermore, programs and interventions should be implemented to improve dietary diversity and reduce the amount of sedentary time spent outside of work among knowledge workers.