Data from version VI-2 of the sixth Korea National Health and Nutrition Examination Survey (KNHANES) performed in 2014 were analyzed. The KNHANES, which is conducted every year by the Korea Centers for Disease Control and Prevention (KCDC), is a nationwide and multistage stratified survey of a representative sample of the South Korean population. Health interviews using questionnaires, health examinations, and blood and urine analyses were performed by trained interviewers, medical staff, and laboratory technicians.17 The PHQ-9, which is a screening tool for depression, was administered to adult KNHANES participants. Among a total of 4,254 subjects aged 40 years and older, 742 who did not complete the PHQ-9 and 25 with missing data on socioeconomic status and health-related behaviors were excluded, and so 3,487 subjects were finally included in the analyses. The VI-2 version of KNHANES was approved by the KCDC Institutional Review Board (approval no. 2013-12EXP-03-5C).

Information on stroke status (diagnosis of stroke, age at stroke diagnosis, current stroke treatment, and stroke complications) was acquired through face-to-face health interviews using a questionnaire. The presence of stroke was diagnosed by a medical doctor. The age at the diagnosis of stroke was categorized into <60 years or ≥60 years. Whether the stroke was currently being treated was also investigated. Patients with stroke complications were defined as subjects who answered “yes” to the following question: “Do you currently experience sequelae of the stroke?”

The PHQ-9, which is a brief, reliable, and valid measure of depression severity, was used to investigate depressive symptoms.9 The PHQ-9 contains nine symptom-related items that measure the frequency of depressive symptoms over the previous 2 weeks. The response options for each item are 'not at all,' 'on several days,' 'on more than half the days,' and 'nearly every day,' which are scored 0, 1, 2, and 3, respectively. The total PHQ-9 score ranges from 0 to 27, with higher scores indicating more-severe depression. In this study, a PHQ-9 score of ≥10 was taken to indicate the presence of depression, since this tool shows a high sensitivity and specificity for major depression.911

We assessed the demographic information, socioeconomic status, health-related behaviors, and comorbidities of the participants using a health interview and health examination. The household income level was calculated by dividing the total household monthly income by the square root of the household size, with the obtained levels then grouped into quartiles. The educational level was categorized into the following four groups: ≤6 years, 7–9 years, 10–12 years, and ≥13 years. Marital status was classified as single, married, or divorced/separated/widowed. Participation in the National Basic Livelihood Security System program, which is the country's social assistance program, was grouped into none, previous, or current. Smoking status was categorized into never, former, and current. The frequency of alcohol consumption was categorized into none, ≤1 drink/month, 2 drinks/month to 3 drinks/week, and ≥4 drinks/week. Physical activity was divided into two groups based on regularity. Body mass index (BMI) was calculated as the body weight divided by the height squared, and categorized into underweight (<18.5 kg/m²), normal (18.5–22.9 kg/m²), overweight (23.0–24.9 kg/m²), and obese (≥25.0 kg/m²). All subjects were asked whether they had received a physician’s diagnosis of major comorbidities such as hypertension, diabetes mellitus, dyslipidemia, ischemic heart disease, major cancers (lung, stomach, liver, colon, breast, or uterine cervical), asthma, pulmonary tuberculosis, arthritis, or chronic renal failure.

Differences in baseline characteristics according to stroke diagnosis were evaluated using the chi-square test for categorical variables and Student's t-test for continuous variables. To examine the association between stroke status and depression, we dichotomized the PHQ-9 scores into normal (≤9) and depressed (≥10). The prevalence of depression was compared according to stroke status (diagnosis of stroke, age at stroke diagnosis, current stroke treatment, and stroke complications) using the chi-square test. Multiple logistic regression was used to evaluate the association between stroke status and depression using four different models. Model 1 was unadjusted, while model 2 was adjusted for age, gender, household income, education, participation in the National Basic Livelihood Security System program, and marital status. Model 3 was adjusted for the same factors as model 2 as well as smoking status, alcohol consumption, regular physical activity, and BMI. Model 4 was adjusted for the same factors as model 3 as well as comorbidities including hypertension, diabetes mellitus, dyslipidemia, ischemic heart disease, major cancer, asthma, pulmonary tuberculosis, arthritis, and chronic renal failure. All statistical analyses were performed using IBM SPSS version 22.0 (SPSS, Chicago, IL, USA). A probability value of p<0.05 was considered statistically significant.

Baseline characteristics of the study population according to diagnosis of stroke are presented in Table 1. Stroke was diagnosed in 120 of the 3,487 subjects (3.4%). Subjects with stroke diagnoses were older than nonstroke controls (p<0.001). Household income, education, marital status, participation in the National Basic Livelihood Security System program, alcohol consumption, and the prevalence rates of hypertension, diabetes mellitus, dyslipidemia, ischemic heart disease, arthritis, and chronic renal failure differed significantly between stroke patients and controls.

The prevalence of depression was higher in stroke patients (16.7%) than in nonstroke controls (6.4%, p<0.001), and higher in patients with stroke diagnosis before 60 years of age (26.0%) than in patients who were older at stroke diagnosis (10.3%, p=0.025). The prevalence of depression differed significantly according to the presence of current stroke treatment and stroke complications (both p<0.001) (Table 2).

The odds ratios (ORs) and 95% confidence intervals (CIs) for depression (PHQ-9 score ≥10) according to stroke status are listed in Table 3. According to the unadjusted model (model 1), the OR for stroke patients for depression relative to nonstroke controls was 2.95 (95% CI, 1.79–4.86). Although additional adjustments for demographic characteristics, socioeconomic status, health-related behaviors, and comorbidities attenuated this relationship, a diagnosis of stroke remained an independent predictor of depression (model 4: OR, 1.85; 95% CI, 1.06–3.24).

Stroke diagnosis before 60 years of age was associated with a higher risk of depression compared with nonstroke controls in all models (model 1: OR, 5.18; 95% CI, 2.71–9.89; model 4: OR, 3.82; 95% CI, 1.81–8.09), whereas stroke diagnosis at age 60 years or older was not a significant predictor of depression. Depression was also more common in stroke patients with an age at diagnosis of less than 60 years relative to those with an older diagnosis (fully adjusted OR, 3.88; 95% CI 1.28–11.75) (data not shown).

While the risk of depression was higher in stroke patients currently receiving treatment than in nonstroke controls in models 1, 2, and 3, this association was not significant in model 4. Compared with nonstroke controls, the presence of stroke complications resulted in a higher risk of depression in all models (model 1: OR, 4.77; 95% CI, 2.38–9.54; model 4: OR, 2.77; 95% CI, 1.25–6.13), whereas having no complications and recovering from complications were not significant predictors of depression.