Korean Elderly Research Articles

Association of Seaweed Consumption with Metabolic Syndrome and Its Components: Findings from the Korean Genome and Epidemiology Study.

This study aimed to investigate the association between seaweed consumption and the odds of developing metabolic syndrome in middle-aged and elderly Koreans. The study included 5777 adults aged 40–69 years from 2001 to 2002 in the Ansan and Ansung cohorts of the Korean Genome and Epidemiology Study. Data on the consumption of seaweed, including laver and kelp/sea mustard, were obtained using a semiquantitative food frequency questionnaire. Multivariable logistic regression models were used to assess the association between seaweed consumption and the odds of developing metabolic syndrome and its components. Women in the highest tertile of laver consumption had lower odds of developing metabolic syndrome than those in the lowest tertile (adjusted odds ratio [AOR]: 0.70; 95% confidence interval [CI]: 0.54–0.92). Both men and women in the highest tertile of laver consumption had lower odds of abdominal obesity than those in the lowest tertile (AOR: 0.64, 95% CI: 0.42–0.98 for men; AOR: 0.53, 95% CI: 0.39–0.72 for women). These findings suggest that laver consumption is inversely associated with the odds of developing metabolic syndrome and abdominal obesity in Korean adults.

Modification Effect of PARP4 and ERCC1 Gene Polymorphisms on the Relationship between Particulate Matter Exposure and Fasting Glucose Level.

Particulate matter (PM) has been linked to adverse health outcomes, including insulin resistance (IR). To evaluate the relationships between exposures to PM10, PM2.5–10, and PM2.5; the serum level of fasting glucose, a key IR indicator; and effects of polymorphisms of two repair genes (PARP4 and ERCC1) on these relations, PMs exposure data and blood samples for glucose measurement and genotyping were collected from 527 Korean elders. Daily average levels of PMs during 8 days, from 7 days before examination to the health examination day (from lag day 7 to lag day 0), were used for association analyses, and mean concentrations of PM10, PM2.5–10, and PM2.5 during the study period were 43.4 µg/m3, 19.9 µg/m3, and 23.6 µg/m3, respectively. All three PMs on lag day 4 (mean, 44.5 µg/m3 for PM10, 19.9 µg/m3 for PM2.5–10, and 24.3 µg/m3 for PM2.5) were most strongly associated with an increase in glucose level (percent change by inter-quartile range-change of PM: (β) = 1.4 and p = 0.0023 for PM10; β = 3.0 and p = 0.0010 for PM2.5–10; and β = 2.0 and p = 0.0134 for PM2.5). In particular, elders with PARP4 G-C-G or ERCC1 T-C haplotype were susceptible to PMs exposure in relation to glucose levels (PARP4 G-C-G: β = 2.6 and p = 0.0006 for PM10, β = 3.5 and p = 0.0009 for PM2.5–10, and β = 1.6 and p = 0.0020 for PM2.5; ERCC1 T-C: β = 2.2 and p = 0.0016 for PM10, β = 3.5 and p = 0.0003 for PM2.5–10, and β = 1.2 and p = 0.0158 for PM2.5). Our results indicated that genetic polymorphisms of PARP4 and ERCC1 could modify the relationship between PMs exposure and fasting glucose level in the elderly.

Association between Relative Handgrip Strength and Insulin Resistance in Korean Elderly Men without Diabetes: Findings of the 2015 Korea National Health Nutrition Examination Survey.

BackgroundEvidence regarding the association between handgrip strength (HGS) and insulin resistance in a non-diabetic population is scarce. This study aimed to investigate the association between relative HGS and insulin resistance in older men without diabetes, using a representative sample of the Korean male population.MethodsThe study population comprised 206 participants aged 65–80 years, selected from the 2015 Korea National Health and Nutrition Examination Survey. Insulin resistance was defined as the upper tertile of the homeostatic model assessment of insulin resistance (HOMA-IR). Odds ratios and 95% confidence intervals for insulin resistance were assessed using multiple logistic regression analyses after adjusting for confounding variables.ResultsThe prevalence of insulin resistance decreased with increasing relative HGS. The prevalence in the T1, T2, and T3 groups was 46.0%, 32.2%, and 26.4%, respectively. Compared with the individuals in the highest tertile of relative HGS, the odds ratio (95% confidence interval) for insulin resistance in individuals in the lowest quartile was 2.82 (1.10–7.21) after adjusting for age, smoking, alcohol consumption, aerobic exercise, resistance exercise, systolic blood pressure, total cholesterol, residential area, household income, and education level.ConclusionLower relative HGS was inversely associated with an increased risk of insulin resistance in older Korean men without diabetes. In clinical practice, relative HGS, which is a simple and inexpensive tool, could be a useful measure for identifying older men with insulin resistance. Moreover, these findings suggest that muscle strengthening exercises should be considered to reduce insulin resistance and increase insulin sensitivity.

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.

Gender modified association of oral health indicators with oral health-related quality of life among Korean elders

ObjectiveTo evaluate the association between oral health-related quality of life (OHRQoL) and oral health indicators including dental status, total occlusion force (TOF), number of natural and rehabilitated teeth (NRT), number of natural teeth (NT), and to explore the effect modification on the association by gender among Korean elders.MethodsA total of 675 participants aged 65 or above recruited by a cluster-based stratified random sampling were included in this cross-sectional study. The 14-items Korean version of the Oral Health Impact Profile (OHIP) was used to measure OHRQoL. The responses about OHIP were dichotomized by the cut-off point of 'fairly often' to determine the ‘poor’ versus ‘fair’ OHRQoL. Age, gender, education level, alcohol drinking, smoking, metabolic syndrome, frailty, and periodontitis were considered as confounders. Multiple multivariable logistic regression analyses were applied to assess the adjusted association between oral health indicators and OHRQoL. Gender stratified analysis was also applied to explore the effect modification of the association.ResultsThe prevalence of poor OHRQoL was 43.0%, which was higher in women, less-educated elders, alcohol non-drinkers and frailty elders (p < 0.05). Elders with poor OHRQoL also showed lower values of oral health indicators than elders with fair OHRQoL (p < 0.05). Those with NRT ≤ 24, NT ≤ 14, and TOF < 330 N increased the risk of poor OHRQoL by 2.3 times (OR = 2.26, confidence interval [CI] 1.54–3.31), 1.5 times (OR = 1.45, CI 1.02–2.07), and 1.5 times (OR = 1.47, CI 1.06–2.04), respectively. In women, the association of NRT ≤ 24 with poor OHRQoL increased from OR of 2.3 to OR of 2.4, while, in men, the association of TOF < 330 N with poor OHRQoL increased from OR of 1.5 to OR of 3.2.ConclusionOral health indicators consisting of TOF, NRT, and NT were independently associated with poor OHRQoL among Korean elders. Gender modified the association of TOF and NRT. Preventive and/or curative management for keeping natural teeth and the rehabilitation of missing teeth to recover the occlusal force may be essential for reducing poor OHRQoL.

Incidence of Neurodegenerative Diseases in Elderly Koreans with and without the First Diagnosed Type 2 Diabetes (P1-1.Virtual)

Incidence of Neurodegenerative Diseases in Elderly Koreans with and without the First Diagnosed Type 2 Diabetes (P1-1.Virtual)

Handgrip Strength and Cognitive Function among Elderly Koreans: Insights from the Korean Longitudinal Study of Ageing.

This study aims to assess handgrip strength as a predictor of cognitive decline within men and women in Korea. A random-intercept logistic regression is fit to estimate the status changes in cognitive function throughout all rounds of the KLoSA, a nationally-representative survey of adults aged 45 years and older. Males in the highest quartile were 71.9% less likely to experience cognitive impairment than those in the lowest quartile. The odds of cognitive impairment for men in the third and second quartiles reduced by 62.6% and 60.4% respectively. Similarly, the odds of cognitive impairment for women declined as 72.7%, 63.0%, and 41.8% for fourth, third, and second quartile, respectively, compared with the lowest quartile. These results imply that assessing and monitoring handgrip strength may enable us to identify subgroups of the elderly with higher likelihood of cognitive impairment in Korea.

Effect of Fermented Red Ginseng Concentrate Intake on Stool Characteristic, Biochemical Parameters, and Gut Microbiota in Elderly Korean Women.

Fermented red ginseng (FRG) has been used as a general stimulant and herbal medicine for health promotion in Asia for thousands of years. Few studies have investigated the effects of FRG containing prebiotics on the gut microbiota. Here, 29 Korean women aged ≥ 50 years were administered FRG for three weeks to determine its effect on stool characteristics, biochemical parameters, and gut microbiome. Gut microbial DNA was subjected to 16S rRNA V3–V4 region sequencing to assess microbial distribution in different stages. Additionally, the stool consistency, frequency of bowel movements, and biochemical parameters of blood were evaluated. We found that FRG intake improved stool consistency and increased the frequency of bowel movements compared to before intake. Biochemical parameters such as glucose, triglyceride, cholesterol, low-density lipoprotein cholesterol, creatinine, alkaline phosphatase, and lactate dehydrogenase decreased and high-density lipoprotein cholesterol increased with FRG intake. Gut microbiome analysis revealed 20 specific bacteria after three weeks of FRG intake. Additionally, 16 pathways correlated with the 20 specific bacteria were enhanced after red ginseng intake. In conclusion, FRG promoted health in elderly women by lowering blood glucose levels and improving bowel movement frequency. The increase in bacteria observed with FRG ingestion supports these findings.

Association between Changes in the Regularity of Working Hours and Cognitive Impairment in Middle-Aged and Older Korean Workers: The Korean Longitudinal Study of Aging, 2008-2018.

Changes in the regularity of working hours affect the cognitive function of middle-aged workers. This study investigated the association between alterations in the regularity of working hours and cognitive impairment in middle-aged and elderly Korean workers. The data from the Korean Longitudinal Study of Aging were analyzed and cognitive function was evaluated using the Korean version of the mini–mental state examination. A score of <23 points was defined as cognitive impairment. The effect of changes in the regularity of working hours on cognitive impairment development was assessed using the generalized estimating equation model. Compared with regular working hours group, the odds ratios (ORs; 95% confidence interval) of the “consistently irregular”, “regular to irregular”, and “irregular to regular” groups were 1.56 (1.30–1.88), 1.46 (1.20–1.77), and 1.24 (1.01–1.53), respectively. The risk of cognitive deterioration was found in the “consistently irregular” group. However, only workers with normal working hours in the “regular to irregular” group had a significant risk of cognitive deterioration (1.51 (1.21–1.89)). Altered working hours were associated with cognitive impairment in middle-aged and older workers. The study emphasizes the need to implement a standard work schedule that is suitable for middle-aged workers.

The Study of Muscle Strength and Dietary Quality of the Korean Elderly: Based on the 2014-2018 Korea National Health and Nutrition Examination Survey

The Study of Muscle Strength and Dietary Quality of the Korean Elderly: Based on the 2014-2018 Korea National Health and Nutrition Examination Survey

The Inverse Association of Sarcopenia and Protein-Source Food and Vegetable Intakes in the Korean Elderly: The Korean Frailty and Aging Cohort Study

The aging population contributes to increasing economic and social burden worldwide. Sarcopenia, an age-related degenerative disease and progressive disorder, is characterized by a reduction in skeletal muscle mass and function. This study aims to assess the association between dietary factors and sarcopenia in the Korean elderly using nationwide data. A total of 801 subjects aged 70–84 years were included in this analysis. Subjects were divided into two groups: sarcopenic and nonsarcopenic groups according to the sarcopenia criteria established by the Asian Working Group for Sarcopenia. Nutrient and food intakes were assessed using a 24-h recall method. Logistic regression analysis was used to assess the association between sarcopenia and food group and nutrient intakes. In the multivariable models, the meat/fish/egg/legume food group, vegetable group, and total food intake were inversely associated with the prevalence of sarcopenia. The high intakes of energy, carbohydrate, protein, fiber, zinc, carotene, and vitamin B6 were associated with the lower prevalence of sarcopenia. Therefore, consuming sufficient nutrients through various protein source foods and vegetables will help prevent sarcopenia in the Korean elderly.

High serum folate level is positively associated with pulmonary function in elderly Korean men, but not in women

A limited number of studies have been conducted on the relationship between serum vitamin levels and pulmonary function, particularly in the elderly population. This study attempted to confirm the association between serum vitamin levels (folate, vitamin A, and vitamin E) and pulmonary function in the elderly population of Korea. A total of 1166 subjects (528 men and 637 women) participated in the Korean National Health and Nutrition Examination Survey from 2016 to 2018. Serum levels of folate, vitamin A, and vitamin E were measured in the subjects. The subjects’ pulmonary function measurement items were as follows: forced vital capacity (FVC), forced expiratory volume in one second (FEV1), forced expiratory volume in one second/forced vital capacity (FEV1/FVC), forced expiratory flow at 25% and 75% of the pulmonary volume (FEF25–75%), forced expiratory volume in 6 s (FEV6), and peak expiratory velocity (PEV). We performed regression analysis considering FEV1, PEV, FVC, FEF25–75%, and FEV1/FVC and FEV6 as dependent variables. Serum vitamin A levels were not associated with pulmonary function. In elderly men, serum vitamin E levels were negatively correlated with FVC [B = − 0.012, 95% confidence interval (CI) − 0.022 to − 0.003, p = 0.012] and FEV1 (B = − 0.010, 95% CI − 0.115 to − 0.007, p = 0.028). We confirmed a positive correlation of the serum folate level with FEV1 (B = 0.017, 95% CI 0.004–0.030, p = 0.009), FEV1/FVC (B = 0.003, 95% CI 0.001–0.005, p = 0.007), and FEF25–75% (B = 0.031, 95% CI 0.010–0.053, p = 0.005) in elderly men. This study confirmed that high serum folate levels were positively associated with pulmonary function in elderly men in Korea. Further studies are needed to understand the longitudinal effect of folate and its biological mechanism in pulmonary function.

Incidence and Cognitive Decline of Alzheimer's Disease and Other Dementia by Apolipoprotein ε4 Allele Presence: A Community-Based Cohort Study in Korean Elderly.

Objective This study aimed to investigate the role of apolipoprotein E (APOE) ε4 allele to the incidence of dementia and cognitive decline in a cohort of a Korean community. Methods From a community-based dementia-free cohort, 357 participants were genotyped. Participants underwent 2 cognitive assessments separated by a hiatus between 6 to 7 years and were diagnosed as healthy control (n=297), Alzheimer’s disease (AD) (n=44), and other dementia (n=16) at the second assessment. Incidence risk and onset age of disease according to APOE ε4 presence were analyzed in AD and other dementia. Differences in cognitive decline rate depending on APOE ε4 were also examined across all groups. Results The relative risks and onset age of dementia were not different by the presence of the APOE ε4 allele. Cognitive decline was more prominent in the presence of APOE ε4 allele (score change=7.4) than non-presence (score change=3.1), and this interaction was significant only in the AD group (F=10.51, p=0.003). Conclusion The APOE ε4 alleles can be a critical factor in predicting cognitive change for AD in the Korean community population but not in predicting AD incidence. This finding suggest that clinicians consider the presence of APOE ε4 allele examining patients with rapid declining dementia.

Prevalence and Risk Factors of T-Score Spine-Hip Discordance in Patients with Osteoporotic Vertebral Compression Fracture.

BackgroundT-score discordance between the spine and hip is commonly observed when dual energy X-ray absorptiometry (DXA) is used to diagnose osteoporosis. However, information is scarce regarding the prevalence and risk factors for this problem in Korea. This study evaluated the prevalence of major/minor discordance and associated risk factors in elderly Korean patients with osteoporotic vertebral compression fractures (OVCFs).MethodsThis study included 200 patients (37 men, 163 women) treated for thoracic or lumbar compression fractures between January 2015 and August 2021. DXA was performed to examine T-scores and determine the prevalence of discordance, defined as a difference between the T-score categories of the femur and spine in the same individual. The t-tests, χ2 tests, and regression analyses were used to assess the associated risk factors of T-score discordance among the subjects.ResultsT-score concordance, minor discordance, and major discordance were observed in 137 (68.5%), 59 (29.5%), and 4 (2%) patients with OVCFs, respectively. The spinal T-score was lower than the femoral T-score in all major discordance and 81.3% (48/59) of minor discordant cases. Overall, the only factor related to T-score discordance was the age at fracture (odds ratio, -0.01; P=0.014).ConclusionsThe results of this study showed that a significant number of subjects (31.5%) showed spine-hip discordance, even with a mean age in their 80s. More attention should be paid to the appropriate evaluation and management of elderly patients with OVCFs. Moreover, a longitudinal study is necessary to verify the clinical importance of T-score discordance in this population.

Effects of Non-Pharmacological Interventions to Improve the Sleep of Korean Elderly: A Systematic Review

Purpose: This systematic review investigated the effects of non-pharmacological interventions to improve the sleep of the Korean elderly at home and in facilities.Methods: A literature search was performed using electronic databases (RISS, KISS, KMbase, KoreaMed, DBpia) from 2010 to 2021. Participants’ characteristics, intervention characteristics, and measured sleep outcomes were systematically reviewed. A qualitative appraisal of studies was performed using the RoB 2.0 and ROBINS-I tools.Results: Of 954 publications identified, 23 met the inclusion criteria. Two studies were randomized controlled trials and 21 studies were quasi-experimental designs with a non-equivalent control group. The contents of 23 intervention studies that aimed to improve sleep included massage, auricular acupressure therapy, laughter therapy, heat therapy, exercise, and aromatherapy. The Korean Sleep Scale A was the most frequently used sleep instrument, in 18 studies. Most interventions were effective in improving sleep, but some inconsistent results were reported.Conclusion: Non-pharmacological interventions for the improvement of sleep in the elderly are useful as therapeutic interventions as part of nursing care, because they are simple and easy to apply. However, to draw clear conclusions about the effect of interventions, it will be necessary to gather results from intervention studies using rigorous methodologies in the future.

Comparison of Gait variables and Relative Risk of Falls According to Walking Speed During Flat and Obstacles Walking of Fallers and Non-Fallers in Korean Elderly Women

PURPOSE: The purpose of this study was to compare the gait variables and the relative risk of falling between elderly Korean women that fall and do not fall based on the walking speed during flat walking and in the presence of obstacles.METHODS: The study included 148 women, aged 65 years or older (22 fallers, aged 75.05±5.38 years; 126 non-fallers, aged 71.80±5.14 years). The gait variables were measured in a space of 9 m×1 m, and obstacle walking was measured while crossing obstacles measuring, 5 cm and 30 cm. A t-test, correlation analysis, and logistic regression analysis were performed to compare the gait variables to determine if there was a fall and to analyze the relationship and the risk ratio of a fall at a walking speed.RESULTS: Out of 148 participants, 22 participants (14.9%), fell while walking. During flat ground walking, right step length (p&lt;.01) left step length (p&lt;.05), and stride lengths (p&lt;.01) were smaller in the faller group, while the stance phase (p&lt;.01) and double-support time ratio (p&lt;.05) were smaller in the non-faller group. In obstacle walking, slower walking speeds were observed for the 5-cm obstacles (p&lt;.01) and 30-cm obstacles (p&lt;.05) in the faller group. For the low-speed and medium-high speed groups, the odds ratio of the fall experience was 2.844 (1.125-7.191) (p&lt;.05) for flat gait, 3.585 (1.354-9.491) (p&lt;.05) for the 5 cm obstacle, and 4.877 (1.731-13.742) (p&lt;.01) for the 30 cm obstacle. As the height of the obstacle increased, the fall odds ratio increased.CONCLUSIONS: In the faller group, the step and stride lengths were smaller during flat walking, and the walking speed of the obstacles was low. The low-speed group had a high falling experience odds ratio, and as the height of the obstacle increased, the falling experience odds ratio increased.

Effects of weight misperception on the association between BMI and self-rated health in midlife and elderly Koreans

ObjectivesThis study aimed to find whether weight misperception affected the relationship between measured body mass index (BMI) and self-rated health (SRH) in middle-aged and senior Koreans. MethodsA cross-sectional study was conducted in 8397 men and 11,211 women aged 40–80 years from the 2014–2018 Korea National Health and Nutrition Examination Survey using gender and age group (40–59 years and 60–80 years) specific moderation analysis and ordinal regression analysis of complex sampling design. BMI and weight misperception were the predictor and moderator, respectively. Outcome measure was SRH graded on very good to very poor scale. ResultsIn the group with accurate body weight estimation, the odds ratio of poorer SRH was greater in underweight or obese men and women aged 40–59 years and women aged 60–80 years compared to normal weight. However, in men aged 60–80 years who accurately estimated their weight, the odds ratio was higher in the underweight group but not in obese group. In the group that overestimated body weight, the odds ratio increased as the BMI category increased. In the group underestimating body weight, the odds ratio decreased in overweight or obese group than in the normal weight group. ConclusionsWeight misperception in middle-aged and older Korean men and women altered the relationship between BMI category and poorer SRH. Individuals who accurately estimated themselves as underweight regardless of gender or age and those who correctly identified themselves as obese in their middle years were the most likely to have poorer SRH.

The Development of a Suicidal Ideation Predictive Model for Community-Dwelling Elderly Aged >55 Years.

PurposeSuicide is an important health and social concern worldwide. Both suicidal ideation and suicide rates are higher in the elderly population than in other age groups; thus, more careful attention and targeted interventions are required. Therefore, we have developed a model to predict suicidal ideation in the community-dwelling elderly aged of >55 years.Patients and MethodsA random forest algorithm was applied to those who participated in the Korea Welfare Panel. We used a total of 26 variables as potential predictors. To resolve the imbalance in the dataset resulting from the low frequency of suicidal ideation, training was performed by applying the synthetic minority oversampling technique. The performance index was calculated by applying the predictive model to the test set, which was not included in the training process.ResultsA total of 6410 elderly Korean aged of >55 (mean, 71.48; standard deviation, 9.56) years were included in the analysis, of which 2.7% had suicidal ideation. The results for predicting suicidal ideation using the 26 chosen variables showed an AUC of 0.879, accuracy of 0.871, sensitivity of 0.750, and specificity of 0.874. The most significant variable in the predictive model was the severity of depression, followed by life satisfaction and self-esteem factors. Basic demographic variables such as age and gender demonstrated a relatively small effect.ConclusionMachine learning can be used to create algorithms for predicting suicidal ideation in community-dwelling elderly. However, there are limitations to predicting future suicidal ideation. A predictive model that includes both biological and cognitive indicators should be created in the future.

Risk Assessment of Mortality in Elderly Individuals: A Nationwide Cohort Study

Introduction: There are several methods that are used to predict emergency room visits or rehospitalization for the elderly. However, existing risk assessment models of mortality in elderly people are limited. The purpose of this study was to ascertain the factors that affect all-cause mortality and to show the risk assessment model of mortality in elderly Koreans. Methods: This was a cohort study conducted using the health checkup data of 246,422 individuals aged ≥60 years, which was provided by the National Health Insurance Service of South Korea between January 1, 2009, and December 31, 2012. The hazard ratios and 95% confidence intervals (CIs) of several conditions and all-cause deaths were estimated using a multivariable Cox proportional hazards model. A nomogram was constructed to visualize the risk factors of mortality; a calibration plot and area under the curve (AUC) were also used to verify the nomogram. Results: Being 85 years or older (100 points) had the greatest influence on all-cause mortality, followed by being underweight (57 points), having more than five chronic diseases (49 points), and ages 78–84 years (45 points); smoking and lack of regular exercise affected mortality to a similar degree. The calibration curves showed good agreement between predictions and observations. The AUC of our nomogram was 0.73 (95% CI: 0.72–0.73). Conclusions: Our results showed the relationship between each condition and mortality rate among elderly individuals in Korea. Our nomogram showed a satisfactory performance in the assessment of the risk of all-cause mortality in elderly Korean people.

Two Opposing Roles of SARS-CoV-2 RBD-Reactive Antibodies in Pre-Pandemic Plasma Samples From Elderly People in ACE2-Mediated Pseudovirus Infection.

A novel coronavirus designated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged and caused an outbreak of unusual viral pneumonia. Several reports have shown that cross-reactive antibodies against SARS-CoV-2 also exist in people unexposed to this virus. However, the neutralizing activity of cross-reactive antibodies is controversial. Here, we subjected plasma samples from SARS-CoV-2-unexposed elderly Korean people (n = 119) to bead-based IgG antibody analysis. SARS-CoV-2 S1 subunit-reactive IgG antibody analysis detected positive signals in some samples (59 of 119, 49.6%). SARS-CoV-2 receptor-binding domain (RBD)-reactive antibody levels were most significantly correlated with human coronavirus-HKU1 S1 subunit-reactive antibody levels. To check the neutralizing activity of plasma samples, the SARS-CoV-2 spike pseudotype neutralizing assay was used. However, the levels of cross-reactive antibodies did not correlate with neutralizing activity. Instead, SARS-CoV-2 pseudovirus infection was neutralized by some RBD-reactive plasma samples (n = 9, neutralization ≥ 25%, P ≤ 0.05), but enhanced by other RBD-reactive plasma samples (n = 4, neutralization ≤ -25%, P ≤ 0.05). Interestingly, the blood plasma groups with enhancing and neutralizing effects had high levels of SARS-CoV-2 RBD-reactive antibodies than the plasma group that had no effect. These results suggest that some SARS-CoV-2 RBD-reactive antibodies from pre-pandemic elderly people exert two opposing functions during SARS-CoV-2 pseudovirus infection. In conclusion, preformed RBD-reactive antibodies may have two opposing functions, namely, protecting against and enhancing viral infection. Analysis of the epitopes of preformed antibodies will be useful to elucidate the underlying mechanism.