Korea National Health And Nutrition Examination Survey Data Research Articles

National trends in the prevalence of hepatitis B and C in South Korea, before and during the COVID-19 pandemic (2007-2021) - a nationwide representative study.

Due to the various changes caused by the COVID-19 pandemic, some infectious diseases showed different epidemiology and prevalence during the pandemic. However, there is a lack of comprehensive studies on trends in the prevalence of hepatitis B and C related to the pandemic. Thus, we compared the prevalence of hepatitis B and C before and during the COVID-19 pandemic in South Korea. We conducted a comprehensive trend analysis with a nationwide serial cross-sectional survey from 2007 to 2021 (n=86,931) using the Korea National Health and Nutrition Examination Survey (KNHANES). The changes in the prevalence of hepatitis B and C were evaluated using a weighted regression model to assess the impact of the COVID-19 pandemic. From 2007 to 2021, 86,931 Korean adults aged 19 or older were included in the KNHANES data. The prevalence of hepatitis B showed a declining trend until the onset of the pandemic (1.80% in 2007-2009; 1.08% in 2016-2019; and 1.01% in 2020), at which point this trend reversed (1.39% in 2021). The prevalence of hepatitis C remained stable (0.14% in 2007-2009 and 0.18% in 2016-2019), with no particular surge related to the COVID-19 pandemic (βdiff, -0.002; 95% CI, -0.761 to 0.756). For hepatitis B, old age was identified as a pandemic-related vulnerable factor (ratio of odds ratio, 1.68; 95% CI, 1.05-2.70). In this study, unlike other infectious diseases, hepatitis B and C did not show a decreasing trend during the pandemic. In particular, hepatitis B showed a rebound trend during the pandemic, which was noticeable in those aged 60 or older. Further studies are needed to support these findings.

Interactive associations of smoking and physical activity with metabolic syndrome in adult men in Korea.

This study aimed to investigate the association of smoking and physical activity (PA) with metabolic syndrome (MetS) in adult men in Korea. This study analyzed data of 7,229 adult men aged 19-64 years obtained from the 2014-2021 Korea National Health and Nutrition Examination Survey (KNHANES). Information on smoking habits was obtained using KNHANES data, while that on total PA (TPA), leisure-time PA (LTPA), and occupational PA (OPA) was collected using the Global Physical Activity Questionnaire. Smoking status was classified into non-smokers and smokers, and PA was categorized into three groups (total, leisure time, and occupational) according to the time spent engaging in moderate or high-intensity PA areas. The diagnosis of MetS was based on the Adult Treatment Program III of the National Cholesterol Education Program and Koreans' waist circumference criteria. Logistic regression revealed that the risk of MetS was significantly lower in non-smokers than in smokers, even after adjusting for all covariates. The risk of MetS was significantly lower in individuals who engaged in at least 150 min of moderate- and high-intensity TPA or LTPA per week than in those who did not engage in PA. Furthermore, smokers who engaged in at least 150 min of moderate- to high-intensity TPA and LTPA per week had a significantly lower risk of MetS than those who did not engage in PA. Meanwhile, OPA was not associated with MetS. The findings suggest that engaging in moderate- to high-intensity TPA or LTPA for at least 150 min per week attenuates the risk of MetS caused by smoking.

Association between Stroke and Abdominal Obesity in the Middle-Aged and Elderly Korean Population: KNHANES Data from 2011-2019.

Obesity and overweight status are primary risk factors for stroke. A relative small number of studies has analyzed the association of abdominal obesity, a crucial indicator for insulin resistance with stroke, compared to general obesity. We aimed to reveal 31,490 records from the Korea National Health and Nutrition Examination Survey (KNHANES). Logistic regression was used to identify the association of abdominal obesity with the risk of stroke. For the multivariate model, covariates were determined based on the cardio-cerebro vascular prediction models. In the sex-specific multivariate logistic regression analysis (including age, antihypertensive drug, diabetes, current smoking, and systolic blood pressure as confounders), the elevated waist circumference (WC) in women was significantly associated with the increased risk for stroke. In case of the categorized form of WC, we discerned the non-linear relationships between WC and the stroke status. The sex-specific associations between the abdominal obesity and stroke status were shown and their relationship pattern exhibited non-linear relationships.

Dietary Reference Intakes for Koreans with special consideration to older adults.

BACKGROUND/OBJECTIVESThe Dietary Reference Intakes for Koreans (KDRIs) were revised in 2020. Due to the rapidly aging Korean population, special consideration was given to reclassify the KDRI age group categories of older adults. This article examines the evidence for modifying the current KDRI age group ranges of older adults (65–74 and ≥ 75 yrs).SUBJECTS/METHODSWe first reviewed the domestic and international data on the elderly, following which we received expert opinions on age classification from the KDRI Advisory Committee. Finally, the 6th and 7th (2013–2017) Korea National Health and Nutrition Examination Survey (KNHANES) data were used to analyze the nutritional intake statuses by considering the age of older adults.RESULTSAccording to the review results of domestic and international data and the inputs received from the expert advisory committee, the minimum age considered for the elderly was maintained at 65 yrs. However, the KNHANES data was analyzed to review whether there was a need to subdivide the later periods. Examining the differences in nutrient intakes by age group through the interaction effect term of the piecewise linear regression model revealed the interaction effect was maximum in the groups divided by 65 yrs (50–64 and 65–80), as compared to the groups divided by 70 yrs (50–69 and 70–80) and 75 yrs (50–74 and 75–80). The mean adequacy ratio was calculated per 1 yr of age, and a 3-yr (age) moving average analysis was performed to examine the change in the trends of overall nutrient intake. However, it was challenging to secure a scientific basis for subdivision into age groups in older adults from the results obtained.CONCLUSIONSThis study could not find any scientific evidence for modifying the KDRI age groups for older adults.

Region-specific COVID-19 risk scores and nutritional status of a high-risk population based on individual vulnerability assessment in the national survey data

Background & aimsCoronavirus disease 2019 (COVID-19) is an ongoing pandemic outbreak leading to more than 1 million deaths worldwide as reported in 2020. Several risk assessment tools, including individual vulnerability to COVID-19, have been developed. The present study aimed to characterize a high-risk population using such a tool and examine risk factors and nutritional status in the national survey data and estimate the region-specific population size.MethodsThe study included 17,540 Korean adults who participated in the Korea National Health and Nutrition Examination Survey (KNHANES). The risk scores for individual vulnerability to COVID-19 were calculated based on age, sex, smoking status, and comorbidities, and a high-risk population was defined as having risk scores ≥11. Nutritional status was compared between the high-risk population and the remaining participants in the KNHANES data. The region-specific population size was estimated using national statistics.ResultsThe proportion of the high-risk population was estimated to be 10.5%, which corresponds to approximately 4.6 million adults in South Korea. About 20% of them had inadequate intake of all of vitamins A, B1, B2, B3, and C below the estimated average requirement. The high-risk population showed 1.65 [95% confidence interval: 1.39, 1.96] higher odds of inadequate intake of multiple vitamins than the remaining participants. In the ecological analysis, the region-specific numbers of the high-risk population correlated significantly with the actual numbers of deaths due to COVID-19 (P value = 0.013).ConclusionsThese results suggest that individuals vulnerable to COVID-19, in particular those are living in densely populated regions, should pay particular attention to the protection against this pandemic and have adequate nutritional status, which may support optimal immune function.

Twenty-year trends in vegetable consumption by preparation method and eating location for Korean population from 1998 to 2017

Vegetables are an important source for the essential vitamins and minerals that are necessary for optimal health. This research investigated changes in vegetable intake over time in the Korean population from 1998 to 2017, focusing on preparation methods of vegetables and location of consumption. This cross-sectional study is based on the Korea National Health and Nutrition Examination Survey (KNHANES) that was established in 1998 to assess the health and nutritional status of the South Korean population. This research utilised information from 1998 to 2017 which is the extent of all available KNHANES data. Vegetable consumption was grouped, according to preparation methods and common eating locations. Both crude and age-standardised means of vegetable intake were derived via a 24-h dietary recall. All participants who completed a 24-h dietary recall survey were selected for the analyses. This included 109220 individuals (49069 men and 60151 women) over the course of 20 years of the KNHANES. Total vegetable intake decreased over time (Pfor trends < 0·001), specifically, steamed and salted vegetables (Pfor trends < 0·001). In contrast, Koreans consumed noticeably more raw vegetables from 1998 to 2017 (Pfor trends < 0·001). Vegetable intake at home significantly declined (Pfor trends < 0·001), while that eaten at restaurants or outside the home increased greatly (Pfor trends < 0·001). Over 20 years, Koreans have ingested decreasing amounts of vegetables, but the intake of raw vegetables has escalated. However, the location of vegetable consumption has changed, with an increase at both restaurants and outside the home (approximately 70·0 %).

Low levels of serum urate are associated with a higher prevalence of depression in older adults: a nationwide cross-sectional study in Korea

BackgroundSoluble urate has been shown to serve as an antioxidant, especially in the central nervous system. Although there are intriguing data suggesting that low levels of serum urate are associated with worse outcomes in neurodegenerative diseases, its impact on mental health has not been adequately assessed. Thus, we aimed to investigate the association between serum urate and depression using a large, nationally representative sample.MethodsInformation on participants’ socio-demographic characteristics as well as physical and mental health conditions were retrieved from the Korea National Health and Nutrition Examination Survey (KNHANES) 2016 dataset. The Patient Health Questionnaire (PHQ)-9 was applied to identify depressive symptoms. Analyses were stratified by age: young adults (aged 19–39 years), middle-aged adults (aged 40–59 years), and older adults (aged 60 years and older).ResultsA total of 5332 participants were included. Serum urate concentrations were divided into sex-specific quartiles based on their distribution: ≤ 4.9 (Q1), 5.0–5.7 (Q2), 5.8–6.6 (Q3), and ≥ 6.7 (Q4) mg/dL in men and ≤ 3.7 (Q1), 3.8–4.3 (Q2), 4.4–4.9 (Q3), and ≥ 5.0 (Q4) mg/dL in women. There was a significant negative linear relationship between serum urate quartiles and PHQ-9 scores in older adults (p for trend = 0.020 in men and p for trend = 0.048 in women). Compared to high levels (Q3 and Q4) of serum urate, low levels (Q1 and Q2) were significantly associated with the overall burden of depression in older women (OR 1.78, 95% CI 1.21, 2.61) and clinically relevant depression in older men (OR 3.35, 95% CI 1.16, 9.70), even after adjustment.ConclusionsBased on the KNHANES data, low levels of serum urate are associated with a higher prevalence of depression in older adults. This may have clinical implications for mental health.

Lifestyle-related predictors affecting prediabetes and diabetes in 20-30-year-old young Korean adults.

OBJECTIVESTo investigate lifestyle-related predictors of prediabetes and diabetes in young adults aged 20–39 years using data from the 2014-2016 Korea National Health and Nutrition Examination Survey (KNHANES).METHODSThis study is a cross-sectional, secondary analysis using the KNHANES data. Participants were classified into normal group (fasting plasma glucose [FPG] <100 mg/dL and/or hemoglobin A1c [HbA1c] <5.7%), prediabetes group (FPG 100-125 mg/dL and/or HbA1c 5.7-6.4%), and diabetes group (FPG ≥126 mg/dL and/or HbA1c ≥ 6.5%). The data were statistically analyzed using SPSS software.RESULTSOut of 4,190 participants, 27.7% of men and 16.3% of women were in the prediabetes group and 1.4% of men and 1.3% of women were in the diabetes group. Logistic regression confirmed that age and obesity are predictors of prediabetes and diabetes in both men and women. Additionally low physical activity and low education level are predictors of prediabetes in men and women, respectively (p<0.05).CONCLUSIONSThis study has found that age and increased obesity are predictors of elevated blood glucose in young men and women in their 20s and 30s. A strategy to lower obesity by promoting physical activity in men in their 30s is essential to prevent metabolic syndrome and progression to prediabetes.

Trends in Fermented Food Consumption and Sodium Intake from Fermented Foods for Korean Adults Using the Korea National Health and Nutrition Examination Survey (KNHANES) (P18-025-19)

ObjectivesTo examine the trends in the consumption of fermented foods and sodium intake over time, using data from the Korean National Health and Nutrition Examination Survey (KNHANES). MethodsThis research study is a secondary analysis using KNHANES data from 1998 to 2016 which is a cross-sectional survey. The target population was Korean adults, ages ≥19 years and the total number was 76,199, with 32,324 men and 43,875 women. Assessment of fermented food consumption and sodium intake was conducted via analysis of 24-hour dietary recall data. Multivariate linear regressions and logistic regressions were performed to calculate the P for trends by applying strata, cluster, and sampling weights by SAS PROC SURVEY. Age was standardized for all analyses in order to calculate P for trends for education, income, fermented food consumption, and sodium intake. ResultsA significant decline in fermented food consumption was observed in both men and women (P < 0.0001). Among fermented foods, kimchi consumption was greatly reduced while pickled vegetables consumption showed a marked increase. Similarly, sodium intake from fermented foods significantly declined over time in both men and women (P < 0.0001). ConclusionsThe consumption of fermented foods and sodium intake from fermented foods by Korean adults significantly decreased over time from 1998 to 2016. Funding SourcesN/A.

Standard Audiograms for Koreans Derived through Hierarchical Clustering Using Data from the Korean National Health and Nutrition Examination Survey 2009\u20132012

Assessments of standardized region/population-specific audiological characteristics are needed for provision of effective rehabilitative services through reducing costs associated with hearing aids. This study aims to propose a set of standard audiograms representing the Korean population that were derived by analyzing data from the 2009–2012 Korea National Health and Nutrition Examination Survey (KNHANES), a nationwide epidemiologic study conducted by Korean government organizations. Standard audiograms were derived by applying a hierarchical clustering method from recorded audiologic data that were obtained independently at 6 frequencies for each ear: 0.5, 1.0, 2.0, 3.0, 4.0, and 6.0 kHz (in dB HL). To derive the optimal number of clusters of the desired standard audiograms, cubic clustering criterion, pseudo-F-, and pseudo-t2-statistics were calculated. These analyses resulted in 29 clusters representing a standard audiogram of the South Korean population. Eighteen of the clusters represented normal hearing audiograms (73.11%), while 11 represented hearing-impaired (HI) standard audiograms (27.89%). Of the 11 HI audiograms, 7 were defined as flat-type (17.81%), while the remaining 4 were defined as sloping-type (9.08%). In conclusion, 29 audiograms representing standard audiograms for the Korean population have been derived using KNHANES data. Improved understanding of the characteristics of each cluster may be helpful for development of more personalized, fixed-setting hearing aids.

Effect of the Standardization of Diagnostic Tests on the Prevalence of Diabetes Mellitus and Impaired Fasting Glucose.

BackgroundWithout standardization of medical laboratory's testing practices, there is an increase in false diagnoses when relying on test results. However, the effect of test standardization is difficult to assess numerically. This study's purpose is to quantify the effect of the standardization level of a laboratory on the prevalence of diabetes mellitus (DM) and impaired fasting glucose (IFG).MethodsLaboratories were classified into three levels: ‘highly-standardized laboratory,’ ‘basically-standardized laboratory,’ and ‘non-standardized laboratory.’ Based on the results of Korean External Quality Assessment Scheme (KEQAS), the cutoff values for diagnosis of DM and IFG were recalculated, given false positive and false negative rates.ResultsThe prevalence of DM and IFG in the population as a whole was estimated using the 2013 Korea National Health and Nutrition Examination Survey (KNHANES) database. When the prevalence of DM from KNHANES was 11.88% (95% confidence interval [CI], 10.59%–13.17%), the proportion with a systematic false error ranged from 10.91% (95% CI, 9.65%–12.17%) to 13.09% (95% CI, 11.74%–14.45%). The prevalence of IFG varied from 13.59% (95% CI, 12.25%–14.91%) to 40.49% (95% CI, 38.54%–42.43%), in contrast to 24.58% (95% CI, 22.85%–26.31%) of the reference value. The prevalence of DM and IFG tended to be over- and under-estimated more as the laboratory standardization level became lower, respectively.ConclusionOur study proved that standardization of clinical laboratory tests is an important factor affecting the prevalence estimation of national disease statistics based on the simulation using KNHANES data.

Development and Validation of the Activities of Daily Living Short Form for Community-Dwelling Korean Stroke Survivors.

This study developed and validated a short form (SF) using activities of daily living (ADL) outcome measures from the Korea National Health and Nutrition Examination Survey (KNHANES) that can minimize survey administration burden for clinicians. This study utilized secondary data from the 2005 KNHANES with 422 community-dwelling stroke survivors. The KNHANES data were collected from April to June 2005 in South Korea. We created a 7-item SF from the 17 ADL questions in the survey using item response theory (IRT) methodologies. The precision and validity of the SF were compared to the full questionnaire of ADL items and the EuroQol-5D total score. Among the 17 ADL questions, 14 questions demonstrated unidimensional construct validity. Using IRT methodologies, a set of 7 items were selected from the full bank. The 7-item SF demonstrated good psychometric properties: high correlation with the full bank ( r = .975, p < .001), good internal consistency (Cronbach's α = .93), and a high correlation with the EuroQol-5D total score ( r = .678, p < .001). These findings indicate that a well-developed SF can precisely measure ADL performance capacity for stroke survivors compared to the full item bank, which is expected to reduce the administration burden of the KNHANES.

The Relationship between Body Mass Index and Homeostasis Model Assessment Index and the Impact of Vitamin D: Based on 2010 Korean National Health and Nutrition Survey

Background: The prevalence of diabetes is increasing worldwide on a daily basis, thus threatening human health. To help control diabetes, considerable research has focused on factors influencing diabetes. Among these factors, obesity is the major cause of diabetes. In addition, vitamin D, which has numerous physiological functions, has been associated with diabetes and obesity. Accordingly, the present study investigated the influence of obesity and vitamin D on diabetes using the Korea National Health and Nutrition Examination Survey (KNHANES) data; we also investigated whether vitamin D is a moderating variable between obesity and insulin resistance, the hallmark characteristic of diabetes. Methods: KNHANES data from January to December 2010 were used. Physical information was obtained via interviews, physical examinations, and self-administered questionnaire surveys; 25-hydroxyvitamin D levels, along with other factors, were measured using blood tests. Those who did not participate in both the survey and blood test were excluded from the present study. Results: A greater degree of insulin resistance was associated with a vitamin D deficiency and a higher body mass index (BMI). However, vitamin D did not modify the association between the BMI and insulin resistance. Conclusion: Although this study aimed to investigate the modulatory action of vitamin D on the association between BMI and insulin resistance, it did not provide evidence of a significant relationship. Insulin resistance was increased in patients with a vitamin D deficiency or a higher BMI. Regular physical activity, especially outdoor activities, as well as vitamin D consumption, are recommended to correct for vitamin D deficiency.

Association of Demographic and Socioeconomic Factors With Risk Factors for Chronic Kidney Disease.

Objectives:The goal of this study was to examine the association of various demographic and socioeconomic factors with risk factors for chronic kidney disease (CKD).Methods:We used nationally representative pooled data from the Korea National Health and Nutrition Examination Survey (KNHANES), 2007–2013. We estimated the glomerular filtration rate (GFR) using the Modification of Diet in Renal Disease equation. We defined CKD as a GFR <60 mL/min/1.73 m2, and 1304 of the 45 208 individuals included in the KNHANES were found to have CKD by this definition. The outcome variable was whether individual subjects adhered to the CKD prevention and management guidelines recommended by the Korea Centers for Disease Control and Prevention. The guidelines suggest that individuals maintain a normal weight, abstain from alcohol consumption and smoking, manage diabetes and hypertension, and engage in regular exercise in order to prevent and manage CKD.Results:This study found that individuals with CKD were more likely to be obese and have hypertension or diabetes than individuals without CKD. In particular, male and less-educated CKD patients were less likely to adhere to the guidelines.Conclusions:Although the prevalence of CKD, as indicated by the KNHANES data, decreased from 2007 to 2013, the prevalence of most risk factors associated with CKD fluctuated over the same time period. Since a variety of demographic and socioeconomic factors are related to the successful implementation of guidelines for preventing and managing CKD, individually tailored prevention activities should be developed.

Application of new guidelines for the primary prevention of atherosclerotic cardiovascular disease in a Korean population.

We investigated the proportion of people who would qualify for statin treatment with an atherosclerotic cardiovascular disease (ASCVD) 10-year risk of ≥7.5% and who exhibit an LDL cholesterol (LDL-C) of 70 to 189 mg/dL according to the new ACC/AHA guidelines for the treatment of increased cardiovascular risk. The study population (8,742 subjects) included individuals who underwent health examinations at Kangbuk Samsung Hospital in South Korea in 2010. We also evaluated the data obtained from the 2008-2010 Korea National Health and Nutrition Examination Survey (KNHANES) of 16,892 adults. Approximately 90% of men ≥60 years of age and women ≥70 years of age had an ASCVD 10-year risk of ≥7.5% and LDL-C level of ≥70 mg/dL. The proportions of subjects with a Framingham 10-year risk of ≥10%, coronary artery calcium score of >20 and >100 and fatty liver each increased in association with an increasing ASCVD 10-year risk quartile in both sexes. Furthermore, age was significantly associated with the ASCVD 10-year risk in both sexes (all p-value <0.001). The KNHANES data also showed that over 85.0% of men ≥60 years of age and 95.0% of women ≥70 years of age had an ASCVD 10-year risk of ≥7.5% and an LDL-C level of ≥70 mg/dL. Adopting the new ASCVD prevention guidelines would result in the treatment of almost all Korean men and women (≥60 years and ≥70 years of age, respectively) without evidence of cardiovascular disease. Therefore, Asian-specific guidelines are needed to avoid unnecessary over treatment in an aging global population.

The Korea National Health and Nutrition Examination Survey as a Primary Data Source

The Korea National Health and Nutrition Examination Survey (KNHANES) is a population-based cross-sectional survey designed to assess the health related behavior, health condition, and nutritional state of Koreans (http://knhanes.cdc.go.kr/). It was conducted as a tri-annual survey for the first 3 cycles, implemented in 1998, 2001, and 2005. Beginning with the 4th cycle of 2007, it was converted to an annual survey. The 2011 data was recently opened to the public, and is free for all researchers who want to use it. The KNHANES provides a rich source of data which are easy to access and can be quickly obtained. Its ethical problems are minimal and there are no adverse effects in conducting the study. Using the KNHANES saves time, money, and personnel that would otherwise be spent collecting data, and provides a larger and higher-quality database beyond the capacity of any one individual researcher. Further, because the study participants are representative of the Korean population, the results have external validity. Therefore, this data is helpful to young investigators. In fact, the portion of submitted articles to the Korean Journal of Family Medicine (KJFM) using the KNHANES as the primary source of data is significant. Specifically, one article in 2007, three articles in 2008, four articles in 2009, three articles in 2010, five articles in 2011, and five articles in 2012 used the KNHANES data as their primary data source, totaling 21 articles (6.2%) among 338 original articles during the previous five years. However, there are several points investigators should keep in mind when using the KNHANES data. First, the KNHANES data are open to the public and there is no systematic process to control the research topic assignment. Many researchers might investigate the same topic simultaneously, especially popular topics like obesity and metabolic syndrome. Before deciding on the study topic, a thorough search of the database like Medline, EMBASE, and the abstracts of related conferences are needed. Once the topic is decided upon, the article should be submitted as soon as possible. Otherwise someone else may publish a similar study from the same dataset before you do. Second, investigators must be familiar with the huge and complex data structure and study design of the KNHANES. Non-response and multi-stage probability sampling should be taken into account by using survey statistics to estimate the data of the whole Korean population. Despite this, lots of studies submitted to KJFM using the KNHANES do not apply sampling weight in their analysis. In such a case the estimated association might be biased and revision is required. Third, the KNHANES is a secondary data source like the Korea Youth Risk Behavior Web-based Survey and the Community Health Survey, and has the same limitations that they have.1) The main purpose of the KNHANES is to produce national statistics, not to answer a specific research question. Therefore, the particular information the investigator wants may not be collected. For these reasons, the dataset should be examined carefully to confirm that it includes the necessary data. There also exists a potential for errors or mistakes in the data, even with its rigorous documents control system. Missing data is also a problem in the KNHANES.2)

Rate of Missing Socioeconomic Factors in the 4th KNHANES

This study is to assess how missing values in socioeconomic status (SES) variables were handled in the Korean Journal of Family Medicine (KJFM) article using the Korea National Health and Nutrition Examination Survey (KNHANES) data and to estimate the rate of missing SES variables from the 4th KNHANES. We searched all original articles published in the KJFM from 2007 to 2011 and identified those that used KNHANES as their primary source of data. None of the 11 articles which presented KNHANES SES variables took into account of omitions in the analysis. The estimated rate of missing data on education, household income, marital status, and occupation data of the 4th KNHANES was 0.3 (0.05)%, 2.7 (0.2)%, 0.5 (0.1)%, and 9.4 (0.9)%, respectively. When all four variables were used simultaneously, the rates increased to 11.8 (0.9)%. Respondents with missing household income tended to be older (P < 0.001), less educated (P < 0.001), and more likely to be unemployed (P < 0.001), and widowed (P < 0.001). A similar relationship was shown for missing occupation data. Omissions in SES variables in KNHANES were related to certain characteristics of study participants. Researchers using KNHANES data should keep in mind the possible bias which can be introduced by missing SES values.