The participants consisted of individuals older than 18 years who underwent a baseline comprehensive health examination at Kangbuk Samsung Hospital Health Screening Center in Seoul and Suwon, South Korea, between 2010 and 2012 and had follow up at 2013. A total of 2623 individuals were identified to have received non-enhanced coronary computed tomography, completed the food frequency questionnaire (FFQ) in addition to questionnaires for depressive symptoms and physical activity at baseline and follow up. The following participants were excluded from analysis: 379 subjects with missing data (on smoking, exercise, and alcohol intake), 44 subjects with a history of cancer, and 52 subjects with a history of cardiovascular disease. As some individuals met more than one criterion for exclusion, the total number of eligible subjects for the study was 2175. Among these subjects we could obtain the answer for questionnaires; 1099 subjects for total energy intake, 917 subjects for composition of macronutrients, 907 subjects for sleep duration and 864 subjects for depression. In Korea, the Industrial Safety and Health Law requires employees to participate in annual or biannual health examinations. Approximately 60 % of the participants were employees of various companies and local governmental organizations.
This study was approved by the Institutional Review Board (IRB) of Kangbuk Samsung Hospital and informed consent requirement was waived as all personal identifiable information was removed prior to accession.
Anthropometric measurements and general characteristics
Body weight and height of subjects were measured to the nearest 0.1 kg and 0.1 cm, respectively. Body mass index (BMI) was calculated as weight in kilograms divided by the square of the height in meters. Obesity was defined as BMI ≥ 25 kg/m2. Data on past medical history, medication use, and health-related behaviors were obtained by a self-administered questionnaire. Questionnaires were used to evaluate education level, smoking status (current or non-current), alcohol consumption (frequency per week, amount) and sleep duration (hours per day). Depression was evaluated by CES-DK score  and food frequency data was calculated by CAN-pro 4.0 (Korean Nutrition Society 2010).
Alcohol intake was examined as unit per day of alcohol consumption. Smokers were divided into two groups: current smoker and non-current smoker. Physical activity was evaluated using the Korean version of the International Physical Activity Questionnaire (IPAQ) short form [20, 21]. The number of days per week and time spent walking per day, as well as moderate and vigorous activities were recorded. The collected data were converted to metabolic equivalent scores (METS) for each type of activity. By multiplying the time engaged in the activity in a week with consideration to the number of METs, metabolic equivalent task minutes per week, MET-min/week, were calculated according to the IPAQ scoring protocol . Blood pressure was measured with electronic sphygmomanometer in the seated position with more than 5 min of resting prior to the measuring.
Coronary Artery Calcification (CAC) measurement
Coronary artery calcification (CAC) was detected by a LightSpeed VCT XTe-64 slice MDCT scanner (GE Healthcare, Tokyo, Japan) with the same standard scanning protocol using 2.5-mm thickness, 400 ms rotation time, 120 kV tube voltage, and 124 mAs (310 mA * 0.4 s) tube current under ECG-gated dose modulation. Coronary artery calcification was defined as more than three contiguous pixels above a CT density of 130 Hounsfield Units. The total CAC score was calculated by Agatston's method . Subjects were classified into two subgroups according to CAC score: CAC group (CAC score >0) or non-CAC group (CAC score ≤ 0) by referring to previous studies.
Blood samples were taken from the antecubital vein, collected in serum-separating tube (SST) after at least 10 h of fasting. Serum levels of total cholesterol and triglyceride were determined using an enzymatic colorimetric assay; low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) levels were directly measured using a homogeneous enzymatic colorimetric assay. Serum fasting glucose level was measured using the hexokinase method. Fasting serum glucose, total cholesterol, LDL-C, HDL-C, triglyceride (TG), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), were measured using Bayer Reagent Packs in an automated chemistry analyzer (Advia 1650 Auto analyzer; Bayer Diagnostics, Leverkusen, Germany). High sensitivity C-reactive protein (hsCRP) was analyzed by particle-enhanced immunonephelometry with the BNII System (Dade Behring, Marburg, Germany). All hematologic measurements were analyzed in one laboratory with the same machines by trained staff using the same methodology throughout. The Korean Society of Laboratory Medicine (KSLM) biannually certified the Laboratory Medicine Department at Kangbuk Samsung Hospital in Seoul, Korea for the Korean Association of Quality Assurance for Clinical Laboratories (KAQACL) and the CAP (Collage of American Pathologists) Proficiency Testing designations.
Nutrient intake measurements
Self-administered food frequency questionnaire (FFQ) was used to obtain nutrient intake data which was designed and validated for use in Korea. Food frequency was estimated by 9 scales (never, 1 time/month, 2 – 3 times/month, 1 – 2 times/week, 3 – 4 times/week, 5 – 6 times/week, 1 time/day, 2 times/day and 3 times/day) and portion size was estimated by three scales (half dish, one dish, one and a half dish) for consumption of 103 food items over the past year. Nutrient intake data include total energy (kcal), carbohydrate (g), protein (g) and fat (g). The Food Composition Table, a nutrient database produced by the Korean Nutrition Society to convert food intake into nutrients, was used to perform nutrient analysis . The contribution of each macronutrient to energy was calculated as the ratio of energy from each macronutrient to total energy: percentage of carbohydrate from total energy intake (%), percentage of fat from total energy intake (%) and percentage of protein from total energy intake (%). Food frequency data was calculated by CAN-pro 4.0 (Korean Nutrition Society 2010). Subjects were categorized into four groups according to each macronutrient intake (Q1 ~ Q4).
Normally distributed variables are presented as the mean ± SD and skewed variables are presented as the median (interquartile range). Continuous variables were compared using independent t-test between CAC change ≤ 0 group and CAC change > 0 group (CAC progression). Categorical variables were expressed as number and percentages then compared between groups using the χ 2 -test. Multiple logistic regression analysis were used to determine Hazard Ratios (HRs) for CAC progression with 95 % confidence intervals (CIs) for quartile groups of each total energy intake, macronutrient intake, physical activity and depression using the lowest quartile group as the reference. To evaluate the significance, two models were constructed. Model 1 was adjusted for age and sex and Model 2 was adjusted for Model 1 and smoking, physical activity, alcohol intake, glucose, triglyceride, HDL-cholesterol, LDL-cholesterol, and blood pressure. P values <0.05 were considered statistically significant. The STATA 11.2 software package was used for statistical analysis.