Eating Alone as a Mediating Factor in the Association Between Living Alone and Depressive Symptoms: A Causal Mediation Analysis Using KNHANES Data = 1인가구와 우울 증상 사이에서 혼밥의 매개효과: 국민건강영양조사 자료를 활용한 인과매개분석

국문 초록 (Abstract)

배경: 우울증은 한국에서 점점 더 심각한 공중보건 문제로 대두되고 있으며, 이는 1인가구의 급속한 증가와 밀접한 관련이 있다. 기존 연구들은 외로움과 사회적 고립을 1인가구와 우울증 간의 주요 매개 요인으로 강조해왔으나, 이러한 요인들은 개념적으로 우울증과 중복되고 표적화된 중재를 제공하는 데에도 한계가 있다. 이와 달리 혼밥은 1인가구의 특성 중 개입이 가능하며, 정신건강 결과 악화와도 독립적으로 연관되어 있다. 본 연구는 혼밥 이 1인가구와 우울 증상 간의 연관성을 매개하는지 조사함으로써 잠재적으로 개입 가능한 행동 경로를 규명하고자 하였다.

방법: 2014년, 2016년, 2018년 국민건강영양조사(KNHANES) 자료를 활용하여 19세 이상 성인 13,729명을 분석하였다. 독립변수는 1인가구, 종속변수인 우울 증상은 한국어판 Patient Health Questionnaire-9 (PHQ-9)을 사용하여 측정하였다. 매개변수인 혼밥은 하루에 동반자 없이 홀로 식사하는 끼니 수를 (0~3회)로 정량화하였다. 평균 인과 매개 효과(ACME), 평균 직접 효과(ADE), 총 효과, 그리고 매개 비율을 추정하기 위한 인과매개분석을 수행하였다. 성별과 연령군별, 거주지역별 하위집단 분석을 추가로 실시하였으며, 연구 결과의 견고성을 평가하기 위한 민감도 분석을 수행하였다.

결과: 전체 참여자의 11.4%가 1인 가구였다. 다인 가구와 비교했을 때, 1인 가구는 유의하게 높은 평균 PHQ-9 점수를 보고하였으며(3.43 vs. 2.36, p < 0.001), 모든 식사를 혼자 섭취하는 비율이 현저히 높았다(40.0% vs. 4.4%). 직접 효과는 통계적으로 유의하지 않았으나(p = 0.431), 혼밥을 매개로 하는 간접 효과는 총 효과의 76.6%를 차지하였으며 통계적으로도 유의하였다(β = 0.060, p < 0.001). 결과는 민감도 분석에서도 견고하게 유지되었으며, 여성과 젊은 성인에서 더욱 뚜렷하게 나타났다.

결론: 1인가구와 우울 증상 간의 연관성은 가구 구성 자체보다 주로 식사동반자의 여부로 설명되었다. 이러한 결과는 식사 행동이 정신건강에 영향을 미치는 주요 메커니즘으로 작용함을 나타낸다. 혼밥을 개입 가능하고 관련성 있는 행동 요인으로 규명함으로써, 본 연구는 한국 1인가구의 우울증 완화를 목표로 하는 표적화된 공중보건 중재 설계에 중요한 함의를 제공한다.

다국어 초록 (Multilingual Abstract)

Background: Depression has emerged as an increasingly pressing public health concern in South Korea, a trend closely linked to the rapid growth of living alone. Previous studies have highlighted loneliness and social isolation as key mediators in this relationship. However, because these factors conceptually overlap with depression itself, they provide limited guidance for the development of targeted interventions. In contrast, eating alone represents a common and observable behavioral characteristic of one-person households, and it has been independently associated with poorer mental health outcomes. This study aimed to investigate whether eating alone mediates the association between living alone and depressive symptoms, thereby identifying a potentially modifiable behavioral pathway.

Methods: Data were drawn from the 2014, 2016, 2018, 2020, and 2022 waves of the Korea National Health and Nutrition Examination Survey (KNHANES), including 13,729 adults aged 19 years and older. The primary exposure variable was living alone, operationalized as residing in a one-person household. Depressive symptoms were measured using the validated Korean version of the Patient Health Questionnaire-9 (PHQ-9). Eating alone was quantified as the number of daily meals (0–3) consumed without companions. Causal mediation analysis was conducted to estimate the average causal mediation effect (ACME), the average direct effect (ADE), the total effect, and the proportion mediated. Subgroup analyses were further performed by sex, age group, and residence area. Also, sensitivity analyses were undertaken to assess the robustness of the findings.

Results: Overall, 11.4% of the participants were living alone. Compared with those living with others, individuals living alone reported significantly higher mean PHQ-9 score (3.43 vs. 2.36, p < 0.001) and were substantially more likely to consume all meals alone (40.0% vs. 4.4%). Living alone was positively associated with depressive symptoms in the total effect model (β = 0.078, p < 0.001). However, the direct effect was not statistically significant (p = 0.431), whereas the indirect effect via eating alone was substantial and statistically significant (β = 0.060, p < 0.001), accounting for 76.6% of the total effect. The results remained robust across sensitivity analyses and were more pronounced among women and younger adults.

Conclusions: The observed association between living alone and depressive symptoms appears to be largely explained by eating alone, rather than household composition itself. These findings underscore the role of eating behaviors as a key mechanism through which living arrangements influence mental health. By identifying eating alone as a modifiable and contextually relevant behavioral factor, this study provides important implications for the design of targeted public health interventions aimed at mitigating depression among individuals living alone in South Korea.

목차 (Table of Contents)

• Abstract i
• Table of Contents iv
• List of Tables vii
• List of Figures viii
• List of Abbreviations ix
• Chapter 1. Introduction 1
• 1.1. Study Background 1
• 1.1.1. Depression 1
• 1.1.2. One-person households 3
• 1.1.3. Eating alone 5
• 1.2. Literature Review 6
• 1.3. Theoretical Framework for Mediation Analysis 9
• 1.3.1. Traditional Mediation Analysis 9
• 1.3.2. Causal Mediation Analysis 13
• 1.4. Purpose of Research 16
• Chapter 2. Methods 17
• 2.1. Datasets 17
• 2.1.1. Data Source 17
• 2.1.2. Study Population 18
• 2.2. Study Variables 20
• 2.2.1. Exposure variable: Living alone 20
• 2.2.2. Outcome variable: Depressive symptoms 20
• 2.2.3. Mediating variable: Eating alone frequency 21
• 2.3. Covariates 22
• 2.4. Statistical Analysis 29
• 2.4.1. Association between eating alone and depressive symptoms 29
• 2.4.2. Causal Mediation Analysis 29
• 2.4.3. Model specification by using mediation package in R 31
• 2.5. Sensitivity Analysis 34
• 2.6. Subgroup Analysis 37
• 2.7. Further Analysis 38
• Chapter 3. Results 39
• 3.1. Baseline Characteristics 39
• 3.2. Association Between Eating Alone and Depressive Symptoms 46
• 3.2.1. Crude model 46
• 3.2.2. Adjusted model 47
• 3.3. Causal Mediation Analysis 49
• 3.3.1. Continuous outcome: PHQ-9 score 49
• 3.3.2. Binary outcome: Cut-off score of 5 51
• 3.4. Sensitivity Analysis 53
• 3.4.1. Rho (ρ) analysis 53
• 3.4.2. Restriction by time since depression diagnosis 55
• 3.4.3. Propensity Score Matching (PSM) 56
• 3.4.4. Binary outcome: Cut-off score of 10 58
• 3.4.5. Covariate Selection and Binary Outcome Estimates 60
• 3.5. Subgroup Analysis 61
• 3.6. Further Analysis 62
• Chapter 4. Discussion 66
• 4.1. Summary of findings 66
• 4.2. Limitations and Conclusions 69
• 4.3. Future works 70
• References 72
• Appendix 81
• 국 문 초 록 85