Insulin resistance was measured using the HOMA-IR, TyG_index, TyG_BMI, TyG_WC, and VAI based on the 2009–2010 KNHANES data.
HOMA-IR is a representative marker of insulin resistance and is calculated using the formula for fasting insulin and fasting glucose levels.
The calculation formulas are as follows: HOMA-IR = fasting insulin (µU/dL) × fasting glucose (mg/dL) / 22.531.
Serum insulin levels were measured using a radioimmunoassay (1470 WIZARD Gamma-Counter; PerkinElmer, Turku, Finland).
The TyG_index is an indirect measure of insulin resistance when insulin measurement is not possible; it uses TG and fasting blood glucose levels instead.
TyG_BMI = TyG_index × BMI32.
TyG_WC = TyG_index × WC32.
TyG_BMI and TyG_WC were obtained by multiplying the TyG_index with BMI and WC, respectively.
The VAI is a marker for assessing the function and distribution of adipose tissue. It is independently associated with the risk of cardiovascular disease and is differentiated between men and women15.
VAI for men: [WC/39.68 + (1.88 × BMI)] × (TG/1.03) × (1.31/HDL-C).
VAI for women: [WC/36.58 + (1.89 × BMI)] × (TG/0.81) × (1.52/HDL-C)33,34.
Anthropometric and biochemical measurements
Experienced examiners performed anthropometric and biochemical measurements. Height (cm) and weight (kg) were measured using Seca 225 (Seca, Hamburg, Germany) and GL-6000-20 (G-tech, Seoul, Korea) instruments, respectively, and BMI was calculated as weight in kilograms divided by height squared in meters. SBP and DBP were measured three times from the right upper arm using a Baumanometer Desk model 0320 (Baum, Charleston, WV, USA). Blood samples were collected after fasting for > 8 h. The samples were stored in a refrigerator prior to the analysis. Fasting plasma glucose, TC, HbA1c, TG, HDL-C, LDL-C, and vitamin D levels were analyzed using a HITACHI Automatic Analyzer 7600 (Hitachi, Tokyo, Japan).
Sociodemographic and lifestyle variables
Sociodemographic and lifestyle variables, including smoking, alcohol consumption, moderate physical activity, walking practice rate, educational level, and income, were assessed. Participants were categorized as current smokers, non-smokers, drinkers, or non-drinkers. Smoking status was determined based on responses to survey questions regarding smoking behavior. “Current smokers” were defined as individuals who had smoked at least 100 cigarettes in their lifetime and reported smoking at the time of the survey, whereas non-smokers were those who had never smoked or had quit smoking.
Alcohol consumption was assessed by categorizing participants as “drinkers” or “non-drinkers.” Drinkers were defined as individuals who reported consuming alcohol in the past month, whereas non-drinkers were those who reported no alcohol consumption during the same period.
Participants were considered moderately physically active if they exercised for more than 30 min per session at least five times a week. Moderate physical activity included slightly strenuous activities that resulted in a mild increase in breathing rate, such as slow swimming, doubles tennis, volleyball, badminton, table tennis, and carrying light objects as part of occupational or physical activities, excluding walking.
The walking practice rate was defined as the frequency participants walked for exercise or transportation. This was categorized based on the number of days per week participants reported walking for at least 30 min.
Participants’ educational backgrounds were classified into four groups: less than elementary school, middle school, high school, and college or higher. Household income was divided into low, lower-middle, upper-middle, and high quartiles.
Awareness of stress was assessed by asking participants to rate their perceived level of stress on a scale from “no stress” to “high level of stress.” Those who reported experiencing a moderate or high level of stress were classified as being “aware of stress.”
Ethics declaration
This study adhered to the guidelines of the Declaration of Helsinki and received approval from the Clinical Trial Screening Committee of Wonkwang University Hospital (approval number: 2024-04-012). Wonkwang University Hospital Institutional Review Board is affiliated with Wonkwang University 3rd General Hospital, located at Wonkwang University Hospital, Sinyong-dong 344–2, Iksan, Jeollabuk-do.
Statistical analysis
Statistical analysis was performed using SPSS for Windows version 26.0, with statistical significance set at p < 0.05.
The KNHANES data are complex survey data; hence, a complex sample analysis considering weights was conducted. Weights were applied according to the guidelines provided by the KNHANES Raw Data Usage Manual of the Korea Centers for Disease Control and Prevention.
Table 1 presents the frequency analysis results using a complex sample design that applied weighted proportions. The general characteristics and differences according to knee OA were compared using the Complex Sample Rao-Scott chi-square test and the Complex Sample generalized linear model. Data are presented as mean ± standard deviation or percentages for nominal variables.
Table 2 presents the results from the complex sample logistic regression test, which examined the impact of the variables for HOMA-IR, TyG_index, and VAI scores on OA. We investigated the influence of insulin resistance-related variables on knee OA. Statistically significant factors were adjusted for ORs and 95% CIs. Model 1 was not adjusted for age, sex, education level, household income, alcohol consumption, and smoking, whereas Model 2 was adjusted for these factors.
In Table 3, the association between the major metabolic syndrome variables (hypertension, dyslipidemia, diabetes, WC, and BMI) and knee OA is examined using ORs and 95% CIs, using the same statistical methods as in Table 2. Table 3 was created in the same manner as Table 2 for Models 1 and 2.
Acknowledgments.
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