Depression is a highly common disorder in psychiatry, often referred to as ‘ the mental cold of modern people’ [1]. Moreover, depression is a significant social issue due to its high association with suicide [2]. According to the results of the Korea National Health and Nutrition Examination Survey (KNHANES), the prevalence of depressive disorder among Korean adults aged 19 and above was 6.7% in 2014, 5.6% in 2016, 4.3% in 2018, 5.7% in 2020, and 5.0% in 2022, showing a prevalence rate of approximately 5-6% [3]. With 22.6 suicides per 100,000 persons in 2022 (against the OECD average of 10.6), South Korea has the highest suicide rate among Organization for Economic Cooperation and Development (OECD) countries. Suicide is also the main cause of death for those between the ages of 10 and 30 [4].

Mental health and physical health doesn’ t operate independently; rather, they influence one another in both directions. Thus, a number of studies [5-17] have investigated the relationship between depression and health behaviors. Smoking [5,6,8,10-12,18] and drinking alcohol [6,12,13] have been linked to an increased risk of depression, according to numerous research. Several studies have reported that increased physical activity is associated with decreased depression [6,9,11,13,14], skipping meals is associated with increased depression, and eating more seafood is associated with decreased depression [6,7,10,17]. However, there has been little research on the impact of mental health on health behaviors (such as smoking, drinking, physical activity, and nutrition), with the majority of studies examining the relationship between mental health and physical health behaviors focusing on the influence of health behaviors on mental health (depression). Although there are some studies on the effects of mental health on health behaviors, most of the studies [19-22] have examined the effects on alcohol consumption and smoking, and there is a lack of research on physical activity and nutrition. Therefore, this study hypothesizes that depression will have a negative impact on health behaviors (smoking, alcohol consumption, physical activity, and nutrition), and by conducting a study to comprehensively confirm this hypothesis, this study aims to provide basic data for the establishment of health care policies.

The current study is to investigate the influence of depression on health behaviors (daily smoking, binge drinking, walking, skipping breakfast) among Korean adults. The important findings and discussions of this study are as follows.

First, our data found that depression increases the likelihood of daily smoking. Previous study [26] targeting 242,952 individuals from low-to middle-income countries has reported a 1.41 increase in the odds of smoking, emphasizing the importance of targeting individuals with depression in smoking cessation programs. Xiaoling et al. [22] found that depression increased the likelihood of smoking, and a systematic review of longitudinal studies in adolescent populations [28] reported that depression predicts smoking. Spring et al. [29] reported that when given a choice of pleasant activities, patients with major depression chose smoking twice as often compared with patients without psychiatric disorders.

Second, our data showed that depression increased the likelihood of binge drinking. A study conducted in the United States found that depression increased the likelihood of binge drinking by 1.18 times [22]. A study [20] targeting elderly individuals with multiple chronic health conditions (MCCs) in the United States insisted that those with MCCs and depression were nearly five times as likely to experience problem drinking as those with MCCs and no depression.

Third, the current study provides an evidence that depression reduce the odds of walking more than five days a week for at least 30 minutes per occasion. A study [21] conducted on Americans indicated that depression reduce the odds of vigorous physical activity by 37.0%, aligning with our findings. A study [19] based on the KNHANES reported that suicidal ideation reduces the odds of physical activity (AOR=0.69), while there was no statistically significant association between depression and physical activity. In the study, depression was assessed using a binary item indicating whether the participants had experienced depression, rather than the PHQ-9 scale. That might have acted as a limitation in the depth and accuracy of depression evaluation.

Fourth, In the current study, depression was associated with an increased likelihood of skipping breakfast for five or more days a week. It was difficult to find studies that examined the effect of skipping breakfast on depression. A few studies [7,10] in adults reported that skipping meals (breakfast or lunch) increases depression, whereas many studies [30,31] in adolescents found that skipping breakfast increases depression. These studies investigated the effect of skipping meals on depression, so they are not directly comparable to the results of our study, which analyzed the effect of depression on skipping meals. However, the findings of these studies are consistent with our analysis in that they show a positive correlation between skipping meals and depression.

The potential associations between depression and health risk behaviors (daily smoking, binge drinking, low walking practices, skipping breakfast) have important implications for health promotion interventions. An and Xiang [22] reported that depression increases smoking and heavy drinking, highlighting that health promotion programs should be mind-ful of these relationships in order to improve intervention effectiveness. In a study of childcare teachers in South Korea, Lee et al. [32] found that depression, social support, and self-efficacy influenced health promotion behaviors, suggesting that mental health care should be considered in physical health promotion programs.

In discussing the limitations of this study, the interpretation of causality between depression and health behaviors has limitations, because the data from the KNHANES used in this study were collected cross-sectionally. Therefore, future longitudinal studies are needed to elucidate the relationship between depression and health behaviors. In addition, depressive experiences were assessed using a self-report questionnaire rather than a physician diagnosis, which may differ from clinical depression [12].

Nevertheless, the current study holds significance for the following reasons. First, the data used in this study were collected through rigorous procedures by a reputable national agency, ensuring representativeness of the entire Korean population through stratified cluster sampling. Therefore, the results of this study can be presented as a general phenomenon among Korean adults. Second, to minimize confounding effects on health behaviors, our study adjusted for variables such as sex, age, household income, education level, and marital status during analysis. Third, our study evaluated the presence of depression more accurate-ly and comprehensively through using the PHQ-9 score, overcoming the limitations of dichotomous responses to a single question like ‘ Do you feel depressed?’ Fourth, most previous studies have primarily focused on investigating the influence of health behaviors (such as smoking, drinking, physical activity and nutrition) on mental health outcomes (such as depression). However, the current study delved into the influence of depression on health behaviors, and sought to fully understand how depression affects all major health behaviors (daily smoking, binge drinking, Low walking practices, skipping breakfast). Therefore, our study found that depression has a negative impact on all major health behaviors.

Our study discovered that depression had a detrimental impact on all main health (daily smoking, binge drinking, walking, skipping breakfast). Our findings indicate that addressing depression is essential for enhancing physical health, and it is imperative to focus on individuals with depression in physical health promotion initiatives.