Introduction: Previous studies have variably reported inconclusive trends in the prevalence of atopic dermatitis (AD) among adults, and there are limited data on the impact of the COVID-19 pandemic. We aimed to investigate the national trends and age-stratified prevalence of AD among adults from 2007 to 2021 in South Korea, focusing mainly on the impact of the COVID-19 pandemic-related factors. Methods: A nationwide cross-sectional study was conducted using the Korea National Health and Nutrition Examination Survey data from 2007 to 2021. Overall and age-stratified prevalence for AD were assessed using weighted beta coefficients or odds ratios. Results: A total of 83,566 adults over 20 years (male, 49.40%) were included. During the observation period, the prevalence of AD was stable in the overall population from 2.61% (95% CI, 2.29–2.93) in 2007–2009 to 2.15% (1.68–2.63) in 2020 and 2.38% (1.81–2.95) in 2021. However, the weighted prevalence of AD in adults aged 40–59 years old decreased during the pre-pandemic era, and the prevalence of AD in adults aged above 60 years significantly decreased during the pandemic, with a significant decline observed after the initial outbreak. From age-stratification analysis, the adults aged 40–59 years showed a significant increase after the pandemic outbreak which was evident in specific variables: individuals with rural residence, lower education, and lower household income quartiles. Adults aged above 60 years showed a significant decrease in the slope after the outbreak, evident in specific variables: individuals of female, rural residence, lower education, and lower household income quartiles. Conclusion: We observed a stable overall prevalence of AD throughout the 15-year observation period. However, the age-stratified analysis suggested significantly different trends according to age-stratified groups and the impact of the COVID-19 pandemic on the prevalence of AD.

Allergic disorders such as atopic dermatitis (AD) are most commonly observed in children but are increasingly recognized as a cause of significant morbidity and have long-term effects even in adults, leading to impaired quality of life and economic burden [1]. While the COVID-19 pandemic has brought unprecedented challenges to healthcare systems, its specific impact on the prevalence of AD among adults remains unexplored [2, 3]. Pandemic-related factors such as increased handwashing, utilization of personal protective equipment, and elevated psychosocial stress could be potential modifiers for the development and symptoms of AD; however, studies exploring the impact of the pandemic on the prevalence of AD among adults are lacking [4, 5].

Previous studies have variably reported increasing and decreasing trends in AD prevalence among adults, suggesting inconclusive evidence indicating the need for further study [6‒8]. Moreover, these studies had methodological limitations, including limited sample sizes and shorter durations of follow-up, predominantly focusing on children [6, 9, 10]. Therefore, we aimed to investigate the age-stratified prevalence and national AD trends among adults from 2007 to 2021 in South Korea, focusing particularly on the impact of COVID-19 pandemic-related factors.

Patient Selection and Data Collection

This study used data from the Korea National Health and Nutrition Examination Survey (KNHANES), an annual survey administered by the Korea Disease Control and Prevention Agency (KDCA) from 2007 to 2021 [11, 12]. The study targeted a population of individuals aged ≥20 years, and the dataset incorporated a diverse array of variables encompassing age, sex, place of residence, body mass index (BMI), level of education, income, alcohol consumption patterns, smoking habits, and history of AD [13]. To investigate the prevalence of AD before and during the COVID-19 pandemic, a nationally representative group of 83,566 individuals was collected for the study. The survey spanned a period of 15 years, with participant counts per year group as follows: 16,725 in 2007–2009; 17,599 in 2010–2012; 15,342 in 2013–2015; 23,353 in 2016–2019; 5,323 in 2020; and 5,224 in 2021.

The Institutional Review Board of Kyung Hee University (KHUH 2022-06-042) and the KDCA approved the research protocol. Before their inclusion in the study, all participants provided written informed consent.

Ascertainment of AD

Our study aimed to assess the annual fluctuations in AD prevalence over a 15-year span, spanning from 2007 to 2021. Following an inquiry regarding a current diagnosis of AD within 1 year, respondents with a history of AD diagnosis who had a physician diagnosis of AD within 1 year were subsequently questioned about their current affliction status.

Covariates

The covariates examined in the analysis encompassed a range of factors, which included age stratified into three groups (20–39, 40–59, and ≥60 years), sex (male and female), region of residence (urban and rural) [14], BMI grouping (underweight, normal weight, overweight, and obese), household income stratified into four groups of quartiles (lowest, second, third, and highest), level of education (elementary school or lower, middle school, high school, and college or higher), alcohol consumption (1–5 days/month, ≥6 days/month, and nondrinker), and smoking status (nonsmoker, ex-smoker, and current smoker). BMI categories adhered to the Asian-Pacific guidelines, classifying individuals as underweight (<18.5 kg/m2), normal weight (18.5–22.9 kg/m2), overweight (23.0–25.0 kg/m2), or obese (≥25.0 kg/m2) [15].

Statistical Analyses

The outcomes of our study were conveyed through qualitative data expressed as proportions or percentages. To compare the estimates of relevant factors between pre-pandemic and during the COVID-19 pandemic, weighted multivariate regression models were employed. The results were presented in terms of weighted odds ratios accompanied by their corresponding 95% confidence intervals (CIs) [16‒18]. The investigation into AD prevalence was conducted using data from the KNHANES spanning 2007–2021, categorized into distinct year groups. Weighted complex sampling analysis was implemented to ensure precise estimation, and it minimized the effect of the difference in the number of participants in each year. For statistical analysis, weighted binomial or linear logistic regression models were utilized to compute odds ratios or β-coefficients with 95% CIs. To enhance the reliability of the findings, stratification analysis was carried out, accounting for variables such as age, sex, level of education, region of residence, and income in all regression models. This approach aimed to provide a comprehensive and robust assessment of the association between AD prevalence and the investigated factors. Statistical analyses were performed using SAS software (version 9.4; SAS Institute, Cary, NC, USA) with a two-sided test, and significance was considered at a p value <0.05.

Of 120 participants, 181 participants surveyed for the KNHANES from 2007 to 2021, 36,615 were excluded due to age <20 years or missing information such as age, sex, and socioeconomic status; thus, 83,566 adults aged 20 years and older (male, 49.40% [95% CI, 49.07–49.74]) were finally included in the analyses (Fig. 1). The sociodemographic characteristics of participants are shown in Table 1. The distribution of participants by age group in crude rates (95% CI) is as follows: in overall period (20–39 years, 29.41 [29.10–29.72]; 40–59 years, 37.00 [36.68–37.33]; ≥60 years, 33.59 [33.27–33.91]), in 2020 (20–39 years, 28.18 [26.97–29.39]; 40–59 years, 35.99 [34.71–37.28]; ≥60 years, 35.83 [34.54–37.11]), and in 2021 (20–39 years, 24.31 [23.15–25.47]; 40–59 years, 35.70 [34.40–37.00]; ≥60 years, 39.99 [38.66–41.32]).

Fig. 1.

Study population. BMI, body mass index.

Fig. 1.

Study population. BMI, body mass index.

Close modal
Table 1.

Baseline characteristics of Koreans in rates of crude and weighted, in the data gathered from the KNHANES from 2007 to 2021 (n = 83,566)

Total2007–20092010–20122013–20152016–201920202021
Overall, n 83,566 16,725 17,599 15,342 23,353 5,323 5,224 
Crude rate (95% CI) 
 Age, years (95% CI) 
  20–39 29.41 (29.10–29.72) 33.64 (32.93–34.36) 30.13 (29.45–30.81) 28.68 (27.96–29.40) 27.72 (27.15–28.30) 28.18 (26.97–29.39) 24.31 (23.15–25.47) 
  40–59 37.00 (36.68–37.33) 36.59 (35.86–37.32) 36.94 (36.23–37.65) 37.68 (36.91–38.45) 37.42 (36.80–38.04) 35.99 (34.71–37.28) 35.70 (34.40–37.00) 
  ≥60 33.59 (33.27–33.91) 29.76 (29.07–30.46) 32.93 (32.23–33.62) 33.64 (32.89–34.39) 34.86 (34.25–35.47) 35.83 (34.54–37.11) 39.99 (38.66–41.32) 
 Sex (95% CI) 
  Male 43.02 (42.68–43.35) 42.43 (41.68–43.18) 42.29 (41.56–43.02) 42.23 (41.45–43.01) 43.74 (43.10–44.37) 45.22 (43.88–46.56) 44.18 (42.83–45.53) 
  Female 56.98 (56.65–57.32) 57.57 (56.82–58.32) 57.71 (56.98–58.44) 57.77 (56.99–58.55) 56.26 (55.63–56.90) 54.78 (53.44–56.12) 55.82 (54.47–57.17) 
 Region of residence (95% CI) 
  Urban 78.96 (78.68–79.24) 73.47 (72.80–74.14) 79.12 (78.52–79.72) 80.99 (80.37–81.61) 81.34 (80.84–81.84) 80.22 (79.15–81.29) 78.10 (76.98–79.22) 
  Rural 21.04 (20.76–21.32) 26.53 (25.86–27.20) 20.88 (20.28–21.48) 19.01 (18.39–19.63) 18.66 (18.16–19.16) 19.78 (18.71–20.85) 21.90 (20.78–23.02) 
 BMI group (95% CI) 
  Underweight 4.28 (4.14–4.41) 4.62 (4.30–4.93) 4.55 (4.24–4.86) 4.37 (4.05–4.70) 3.80 (3.55–4.04) 3.91 (3.39–4.43) 4.48 (3.92–5.04) 
  Normal weight 38.95 (38.62–39.29) 39.64 (38.90–40.38) 40.37 (39.65–41.10) 39.48 (38.71–40.25) 38.61 (37.98–39.23) 35.19 (33.90–36.47) 35.83 (34.53–37.14) 
  Overweight 23.31 (23.03–23.60) 23.92 (23.28–24.57) 23.26 (22.63–23.88) 23.59 (22.92–24.26) 22.89 (22.35–23.43) 22.77 (21.64–23.90) 23.16 (22.02–24.31) 
  Obese 33.46 (33.14–33.78) 31.82 (31.11–32.53) 31.82 (31.13–32.51) 32.56 (31.82–33.30) 34.70 (34.09–35.31) 38.14 (36.83–39.44) 36.52 (35.22–37.83) 
 Education (95% CI) 
  Elementary school or lower education 20.99 (20.72–21.27) 26.82 (26.15–27.49) 23.58 (22.95–24.21) 20.95 (20.31–21.59) 17.57 (17.08–18.06) 13.79 (12.86–14.72) 16.37 (15.36–17.37) 
  Middle school 11.08 (10.87–11.29) 11.75 (11.27–12.24) 11.56 (11.09–12.04) 11.34 (10.84–11.84) 10.48 (10.09–10.88) 10.20 (9.39–11.01) 10.09 (9.27–10.90) 
  High school 27.91 (27.60–28.21) 28.84 (28.15–29.52) 28.05 (27.39–28.72) 28.11 (27.39–28.82) 27.00 (26.43–27.57) 27.94 (26.73–29.14) 27.89 (26.67–29.11) 
  College or higher education 40.02 (39.69–40.35) 32.59 (31.88–33.30) 36.80 (36.09–37.52) 39.60 (38.83–40.38) 44.95 (44.31–45.59) 48.07 (46.73–49.42) 45.65 (44.30–47.01) 
 Smoking status (95% CI) 
  Smoker 19.22 (18.95–19.49) 22.12 (21.49–22.75) 20.42 (19.83–21.02) 18.60 (17.99–19.22) 17.89 (17.40–18.39) 16.93 (15.92–17.93) 15.98 (14.99–16.98) 
  Ex-smoker 20.86 (20.59–21.14) 19.34 (18.74–19.94) 20.31 (19.72–20.91) 19.86 (19.23–20.49) 21.84 (21.31–22.37) 23.22 (22.09–24.35) 23.76 (22.60–24.91) 
  Nonsmoker 59.92 (59.58–60.25) 58.54 (57.79–59.29) 59.26 (58.54–59.99) 61.54 (60.77–62.31) 60.27 (59.64–60.89) 59.85 (58.54–61.17) 60.26 (58.93–61.59) 
 Alcohol consumption (95% CI) 
  Nondrinker 13.04 (12.81–13.27) 14.88 (14.34–15.42) 14.51 (13.99–15.03) 13.53 (12.99–14.07) 11.09 (10.69–11.50) 10.78 (9.95–11.62) 11.73 (10.86–12.61) 
  1–5 days/month 65.88 (65.56–66.20) 63.61 (62.88–64.34) 64.74 (64.03–65.44) 65.72 (64.96–66.47) 66.96 (66.35–67.56) 68.83 (67.59–70.08) 69.68 (68.43–70.92) 
  6–30 days/month 21.08 (20.80–21.36) 21.51 (20.89–22.14) 20.75 (20.15–21.35) 20.75 (20.11–21.40) 21.95 (21.42–22.48) 20.38 (19.30–21.47) 18.59 (17.53–19.64) 
 Household income (95% CI) 
  Lowest quartile 19.53 (19.26–19.80) 21.27 (20.65–21.89) 19.63 (19.04–20.21) 19.34 (18.71–19.96) 19.08 (18.58–19.59) 16.81 (15.81–17.82) 18.99 (17.93–20.05) 
  Second quartile 24.93 (24.64–25.23) 24.98 (24.32–25.64) 25.75 (25.10–26.39) 25.36 (24.67–26.05) 24.62 (24.07–25.17) 23.54 (22.40–24.68) 23.58 (22.43–24.73) 
  Third quartile 27.12 (26.82–27.42) 26.67 (26.00–27.34) 27.20 (26.54–27.86) 27.21 (26.51–27.92) 26.94 (26.37–27.51) 28.39 (27.18–29.60) 27.49 (26.28–28.70) 
  Highest quartile 28.42 (28.11–28.72) 27.07 (26.40–27.75) 27.43 (26.77–28.09) 28.09 (27.38–28.80) 29.36 (28.77–29.94) 31.26 (30.02–32.51) 29.94 (28.70–31.18) 
Weighted rate (95% CI) 
 Age, years, weighted % (95% CI) 
  20–39 38.19 (37.59–38.78) 42.71 (41.28–44.15) 40.17 (38.84–41.50) 38.24 (36.96–39.51) 35.77 (34.65–36.89) 35.43 (33.05–37.82) 34.10 (31.87–36.32) 
  40–59 39.71 (39.22–40.20) 38.89 (37.68–40.10) 39.94 (38.88–41.00) 40.13 (39.07–41.18) 40.02 (39.07–40.96) 39.84 (37.67–42.01) 38.44 (36.68–40.19) 
  ≥60 22.11 (21.62–22.59) 18.40 (17.46–19.34) 19.89 (18.90–20.87) 21.64 (20.61–22.66) 24.22 (23.17–25.26) 24.73 (22.38–27.08) 27.47 (25.11–29.82) 
 Sex, weighted % (95% CI) 
  Male 49.40 (49.07–49.74) 49.59 (48.86–50.31) 49.18 (48.41–49.95) 48.80 (48.02–49.57) 49.54 (48.90–50.18) 50.25 (49.16–51.34) 49.90 (48.56–51.25) 
  Female 50.60 (50.26–50.93) 50.41 (49.69–51.14) 50.82 (50.05–51.59) 51.20 (50.43–51.98) 50.46 (49.82–51.10) 49.75 (48.66–50.84) 50.10 (48.75–51.44) 
 Region of residence, weighted % (95% CI) 
  Urban 82.84 (81.53–84.15) 80.69 (77.60–83.77) 80.08 (76.83–83.32) 83.04 (80.18–85.90) 84.98 (82.55–87.41) 85.04 (79.95–90.12) 84.35 (79.38–89.32) 
  Rural 17.16 (15.85–18.47) 19.31 (16.23–22.40) 19.93 (16.68–23.17) 16.96 (14.10–19.82) 15.02 (12.59–17.45) 14.96 (9.88–20.05) 15.65 (10.68–20.62) 
 BMI* group, weighted % (95% CI) 
  Underweight 4.54 (4.36–4.72) 4.82 (4.39–5.24) 4.87 (4.45–5.28) 4.84 (4.41–5.27) 4.06 (3.74–4.38) 4.10 (3.35–4.86) 4.55 (3.89–5.21) 
  Normal weight 38.91 (38.49–39.32) 39.70 (38.82–40.58) 40.19 (39.21–41.17) 40.02 (39.10–40.94) 38.59 (37.81–39.37) 34.16 (32.57–35.76) 36.34 (34.69–37.99) 
  Overweight 22.82 (22.47–23.16) 23.69 (22.94–24.43) 22.70 (21.94–23.47) 22.95 (22.15–23.76) 22.47 (21.83–23.10) 23.06 (21.83–24.29) 21.83 (20.40–23.26) 
  Obese 33.74 (33.32–34.15) 31.80 (30.91–32.70) 32.25 (31.29–33.20) 32.18 (31.29–33.08) 34.89 (34.08–35.70) 38.67 (37.06–40.29) 37.28 (35.47–39.09) 
 Education, weighted % (95% CI) 
  Elementary school or lower education 14.28 (13.88–14.69) 18.27 (17.28–19.25) 16.92 (15.94–17.91) 14.66 (13.75–15.58) 12.18 (11.42–12.93) 9.00 (7.53–10.47) 10.00 (8.40–11.60) 
  Middle school 9.21 (8.94–9.47) 10.57 (9.95–11.18) 10.25 (9.63–10.86) 9.23 (8.66–9.81) 8.49 (7.99–8.99) 7.62 (6.56–8.68) 7.42 (6.43–8.42) 
  High school 29.17 (28.69–29.65) 31.20 (30.10–32.31) 30.33 (29.22–31.44) 29.10 (28.02–30.18) 27.42 (26.53–28.31) 28.70 (26.74–30.66) 28.81 (26.90–30.73) 
  College or higher education 47.34 (46.63–48.06) 39.96 (38.42–41.51) 42.50 (40.99–44.02) 47.01 (45.51–48.51) 51.91 (50.46–53.36) 54.68 (51.42–57.95) 53.76 (50.71–56.82) 
 Smoking status, weighted % (95% CI) 
  Smoker 23.18 (22.78–23.59) 26.96 (26.11–27.81) 26.40 (25.48–27.32) 22.60 (21.67–23.52) 21.20 (20.42–21.97) 19.40 (17.91–20.89) 18.48 (17.01–19.95) 
  Ex-smoker 21.05 (20.73–21.38) 19.88 (19.19–20.57) 19.75 (19.03–20.47) 19.81 (19.07–20.56) 21.87 (21.27–22.47) 24.01 (22.81–25.21) 24.79 (23.40–26.17) 
  Nonsmoker 55.76 (55.36–56.16) 53.16 (52.32–54.00) 53.85 (52.98–54.72) 57.59 (56.68–58.50) 56.93 (56.16–57.71) 56.59 (55.03–58.15) 56.74 (54.97–58.50) 
 Alcohol consumption, weighted % (95% CI) 
  Nondrinker 10.05 (9.78–10.32) 11.62 (11.01–12.24) 11.06 (10.41–11.72) 10.69 (10.05–11.32) 8.79 (8.30–9.27) 8.03 (7.03–9.03) 8.79 (7.73–9.85) 
  1–5 days/month 66.94 (66.52–67.36) 64.86 (63.86–65.85) 65.46 (64.47–66.46) 66.58 (65.60–67.56) 67.77 (67.02–68.52) 69.58 (68.04–71.12) 71.17 (69.70–72.64) 
  6–30 days/month 23.01 (22.64–23.38) 23.52 (22.66–24.38) 23.47 (22.63–24.31) 22.74 (21.88–23.60) 23.44 (22.77–24.11) 22.39 (20.97–23.80) 20.04 (18.68–21.40) 
 Household income, weighted % (95% CI) 
  Lowest quartile 15.37 (14.90–15.85) 16.22 (15.13–17.31) 16.03 (14.99–17.07) 15.31 (14.23–16.40) 15.43 (14.49–16.37) 13.43 (11.38–15.49) 13.37 (11.39–15.34) 
  Second quartile 24.70 (24.14–25.27) 25.02 (23.74–26.30) 27.22 (25.90–28.55) 24.77 (23.46–26.08) 23.97 (22.96–24.97) 21.73 (19.56–23.91) 22.60 (20.46–24.74) 
  Third quartile 29.22 (28.66–29.79) 28.86 (27.58–30.15) 29.14 (27.92–30.36) 29.48 (28.10–30.87) 28.87 (27.84–29.89) 29.88 (27.76–32.00) 30.44 (28.21–32.66) 
  Highest quartile 30.70 (29.92–31.47) 29.89 (28.07–31.72) 27.61 (26.15–29.07) 30.43 (28.67–32.19) 31.74 (30.24–33.23) 34.96 (31.45–38.46) 33.60 (29.76–37.44) 
Total2007–20092010–20122013–20152016–201920202021
Overall, n 83,566 16,725 17,599 15,342 23,353 5,323 5,224 
Crude rate (95% CI) 
 Age, years (95% CI) 
  20–39 29.41 (29.10–29.72) 33.64 (32.93–34.36) 30.13 (29.45–30.81) 28.68 (27.96–29.40) 27.72 (27.15–28.30) 28.18 (26.97–29.39) 24.31 (23.15–25.47) 
  40–59 37.00 (36.68–37.33) 36.59 (35.86–37.32) 36.94 (36.23–37.65) 37.68 (36.91–38.45) 37.42 (36.80–38.04) 35.99 (34.71–37.28) 35.70 (34.40–37.00) 
  ≥60 33.59 (33.27–33.91) 29.76 (29.07–30.46) 32.93 (32.23–33.62) 33.64 (32.89–34.39) 34.86 (34.25–35.47) 35.83 (34.54–37.11) 39.99 (38.66–41.32) 
 Sex (95% CI) 
  Male 43.02 (42.68–43.35) 42.43 (41.68–43.18) 42.29 (41.56–43.02) 42.23 (41.45–43.01) 43.74 (43.10–44.37) 45.22 (43.88–46.56) 44.18 (42.83–45.53) 
  Female 56.98 (56.65–57.32) 57.57 (56.82–58.32) 57.71 (56.98–58.44) 57.77 (56.99–58.55) 56.26 (55.63–56.90) 54.78 (53.44–56.12) 55.82 (54.47–57.17) 
 Region of residence (95% CI) 
  Urban 78.96 (78.68–79.24) 73.47 (72.80–74.14) 79.12 (78.52–79.72) 80.99 (80.37–81.61) 81.34 (80.84–81.84) 80.22 (79.15–81.29) 78.10 (76.98–79.22) 
  Rural 21.04 (20.76–21.32) 26.53 (25.86–27.20) 20.88 (20.28–21.48) 19.01 (18.39–19.63) 18.66 (18.16–19.16) 19.78 (18.71–20.85) 21.90 (20.78–23.02) 
 BMI group (95% CI) 
  Underweight 4.28 (4.14–4.41) 4.62 (4.30–4.93) 4.55 (4.24–4.86) 4.37 (4.05–4.70) 3.80 (3.55–4.04) 3.91 (3.39–4.43) 4.48 (3.92–5.04) 
  Normal weight 38.95 (38.62–39.29) 39.64 (38.90–40.38) 40.37 (39.65–41.10) 39.48 (38.71–40.25) 38.61 (37.98–39.23) 35.19 (33.90–36.47) 35.83 (34.53–37.14) 
  Overweight 23.31 (23.03–23.60) 23.92 (23.28–24.57) 23.26 (22.63–23.88) 23.59 (22.92–24.26) 22.89 (22.35–23.43) 22.77 (21.64–23.90) 23.16 (22.02–24.31) 
  Obese 33.46 (33.14–33.78) 31.82 (31.11–32.53) 31.82 (31.13–32.51) 32.56 (31.82–33.30) 34.70 (34.09–35.31) 38.14 (36.83–39.44) 36.52 (35.22–37.83) 
 Education (95% CI) 
  Elementary school or lower education 20.99 (20.72–21.27) 26.82 (26.15–27.49) 23.58 (22.95–24.21) 20.95 (20.31–21.59) 17.57 (17.08–18.06) 13.79 (12.86–14.72) 16.37 (15.36–17.37) 
  Middle school 11.08 (10.87–11.29) 11.75 (11.27–12.24) 11.56 (11.09–12.04) 11.34 (10.84–11.84) 10.48 (10.09–10.88) 10.20 (9.39–11.01) 10.09 (9.27–10.90) 
  High school 27.91 (27.60–28.21) 28.84 (28.15–29.52) 28.05 (27.39–28.72) 28.11 (27.39–28.82) 27.00 (26.43–27.57) 27.94 (26.73–29.14) 27.89 (26.67–29.11) 
  College or higher education 40.02 (39.69–40.35) 32.59 (31.88–33.30) 36.80 (36.09–37.52) 39.60 (38.83–40.38) 44.95 (44.31–45.59) 48.07 (46.73–49.42) 45.65 (44.30–47.01) 
 Smoking status (95% CI) 
  Smoker 19.22 (18.95–19.49) 22.12 (21.49–22.75) 20.42 (19.83–21.02) 18.60 (17.99–19.22) 17.89 (17.40–18.39) 16.93 (15.92–17.93) 15.98 (14.99–16.98) 
  Ex-smoker 20.86 (20.59–21.14) 19.34 (18.74–19.94) 20.31 (19.72–20.91) 19.86 (19.23–20.49) 21.84 (21.31–22.37) 23.22 (22.09–24.35) 23.76 (22.60–24.91) 
  Nonsmoker 59.92 (59.58–60.25) 58.54 (57.79–59.29) 59.26 (58.54–59.99) 61.54 (60.77–62.31) 60.27 (59.64–60.89) 59.85 (58.54–61.17) 60.26 (58.93–61.59) 
 Alcohol consumption (95% CI) 
  Nondrinker 13.04 (12.81–13.27) 14.88 (14.34–15.42) 14.51 (13.99–15.03) 13.53 (12.99–14.07) 11.09 (10.69–11.50) 10.78 (9.95–11.62) 11.73 (10.86–12.61) 
  1–5 days/month 65.88 (65.56–66.20) 63.61 (62.88–64.34) 64.74 (64.03–65.44) 65.72 (64.96–66.47) 66.96 (66.35–67.56) 68.83 (67.59–70.08) 69.68 (68.43–70.92) 
  6–30 days/month 21.08 (20.80–21.36) 21.51 (20.89–22.14) 20.75 (20.15–21.35) 20.75 (20.11–21.40) 21.95 (21.42–22.48) 20.38 (19.30–21.47) 18.59 (17.53–19.64) 
 Household income (95% CI) 
  Lowest quartile 19.53 (19.26–19.80) 21.27 (20.65–21.89) 19.63 (19.04–20.21) 19.34 (18.71–19.96) 19.08 (18.58–19.59) 16.81 (15.81–17.82) 18.99 (17.93–20.05) 
  Second quartile 24.93 (24.64–25.23) 24.98 (24.32–25.64) 25.75 (25.10–26.39) 25.36 (24.67–26.05) 24.62 (24.07–25.17) 23.54 (22.40–24.68) 23.58 (22.43–24.73) 
  Third quartile 27.12 (26.82–27.42) 26.67 (26.00–27.34) 27.20 (26.54–27.86) 27.21 (26.51–27.92) 26.94 (26.37–27.51) 28.39 (27.18–29.60) 27.49 (26.28–28.70) 
  Highest quartile 28.42 (28.11–28.72) 27.07 (26.40–27.75) 27.43 (26.77–28.09) 28.09 (27.38–28.80) 29.36 (28.77–29.94) 31.26 (30.02–32.51) 29.94 (28.70–31.18) 
Weighted rate (95% CI) 
 Age, years, weighted % (95% CI) 
  20–39 38.19 (37.59–38.78) 42.71 (41.28–44.15) 40.17 (38.84–41.50) 38.24 (36.96–39.51) 35.77 (34.65–36.89) 35.43 (33.05–37.82) 34.10 (31.87–36.32) 
  40–59 39.71 (39.22–40.20) 38.89 (37.68–40.10) 39.94 (38.88–41.00) 40.13 (39.07–41.18) 40.02 (39.07–40.96) 39.84 (37.67–42.01) 38.44 (36.68–40.19) 
  ≥60 22.11 (21.62–22.59) 18.40 (17.46–19.34) 19.89 (18.90–20.87) 21.64 (20.61–22.66) 24.22 (23.17–25.26) 24.73 (22.38–27.08) 27.47 (25.11–29.82) 
 Sex, weighted % (95% CI) 
  Male 49.40 (49.07–49.74) 49.59 (48.86–50.31) 49.18 (48.41–49.95) 48.80 (48.02–49.57) 49.54 (48.90–50.18) 50.25 (49.16–51.34) 49.90 (48.56–51.25) 
  Female 50.60 (50.26–50.93) 50.41 (49.69–51.14) 50.82 (50.05–51.59) 51.20 (50.43–51.98) 50.46 (49.82–51.10) 49.75 (48.66–50.84) 50.10 (48.75–51.44) 
 Region of residence, weighted % (95% CI) 
  Urban 82.84 (81.53–84.15) 80.69 (77.60–83.77) 80.08 (76.83–83.32) 83.04 (80.18–85.90) 84.98 (82.55–87.41) 85.04 (79.95–90.12) 84.35 (79.38–89.32) 
  Rural 17.16 (15.85–18.47) 19.31 (16.23–22.40) 19.93 (16.68–23.17) 16.96 (14.10–19.82) 15.02 (12.59–17.45) 14.96 (9.88–20.05) 15.65 (10.68–20.62) 
 BMI* group, weighted % (95% CI) 
  Underweight 4.54 (4.36–4.72) 4.82 (4.39–5.24) 4.87 (4.45–5.28) 4.84 (4.41–5.27) 4.06 (3.74–4.38) 4.10 (3.35–4.86) 4.55 (3.89–5.21) 
  Normal weight 38.91 (38.49–39.32) 39.70 (38.82–40.58) 40.19 (39.21–41.17) 40.02 (39.10–40.94) 38.59 (37.81–39.37) 34.16 (32.57–35.76) 36.34 (34.69–37.99) 
  Overweight 22.82 (22.47–23.16) 23.69 (22.94–24.43) 22.70 (21.94–23.47) 22.95 (22.15–23.76) 22.47 (21.83–23.10) 23.06 (21.83–24.29) 21.83 (20.40–23.26) 
  Obese 33.74 (33.32–34.15) 31.80 (30.91–32.70) 32.25 (31.29–33.20) 32.18 (31.29–33.08) 34.89 (34.08–35.70) 38.67 (37.06–40.29) 37.28 (35.47–39.09) 
 Education, weighted % (95% CI) 
  Elementary school or lower education 14.28 (13.88–14.69) 18.27 (17.28–19.25) 16.92 (15.94–17.91) 14.66 (13.75–15.58) 12.18 (11.42–12.93) 9.00 (7.53–10.47) 10.00 (8.40–11.60) 
  Middle school 9.21 (8.94–9.47) 10.57 (9.95–11.18) 10.25 (9.63–10.86) 9.23 (8.66–9.81) 8.49 (7.99–8.99) 7.62 (6.56–8.68) 7.42 (6.43–8.42) 
  High school 29.17 (28.69–29.65) 31.20 (30.10–32.31) 30.33 (29.22–31.44) 29.10 (28.02–30.18) 27.42 (26.53–28.31) 28.70 (26.74–30.66) 28.81 (26.90–30.73) 
  College or higher education 47.34 (46.63–48.06) 39.96 (38.42–41.51) 42.50 (40.99–44.02) 47.01 (45.51–48.51) 51.91 (50.46–53.36) 54.68 (51.42–57.95) 53.76 (50.71–56.82) 
 Smoking status, weighted % (95% CI) 
  Smoker 23.18 (22.78–23.59) 26.96 (26.11–27.81) 26.40 (25.48–27.32) 22.60 (21.67–23.52) 21.20 (20.42–21.97) 19.40 (17.91–20.89) 18.48 (17.01–19.95) 
  Ex-smoker 21.05 (20.73–21.38) 19.88 (19.19–20.57) 19.75 (19.03–20.47) 19.81 (19.07–20.56) 21.87 (21.27–22.47) 24.01 (22.81–25.21) 24.79 (23.40–26.17) 
  Nonsmoker 55.76 (55.36–56.16) 53.16 (52.32–54.00) 53.85 (52.98–54.72) 57.59 (56.68–58.50) 56.93 (56.16–57.71) 56.59 (55.03–58.15) 56.74 (54.97–58.50) 
 Alcohol consumption, weighted % (95% CI) 
  Nondrinker 10.05 (9.78–10.32) 11.62 (11.01–12.24) 11.06 (10.41–11.72) 10.69 (10.05–11.32) 8.79 (8.30–9.27) 8.03 (7.03–9.03) 8.79 (7.73–9.85) 
  1–5 days/month 66.94 (66.52–67.36) 64.86 (63.86–65.85) 65.46 (64.47–66.46) 66.58 (65.60–67.56) 67.77 (67.02–68.52) 69.58 (68.04–71.12) 71.17 (69.70–72.64) 
  6–30 days/month 23.01 (22.64–23.38) 23.52 (22.66–24.38) 23.47 (22.63–24.31) 22.74 (21.88–23.60) 23.44 (22.77–24.11) 22.39 (20.97–23.80) 20.04 (18.68–21.40) 
 Household income, weighted % (95% CI) 
  Lowest quartile 15.37 (14.90–15.85) 16.22 (15.13–17.31) 16.03 (14.99–17.07) 15.31 (14.23–16.40) 15.43 (14.49–16.37) 13.43 (11.38–15.49) 13.37 (11.39–15.34) 
  Second quartile 24.70 (24.14–25.27) 25.02 (23.74–26.30) 27.22 (25.90–28.55) 24.77 (23.46–26.08) 23.97 (22.96–24.97) 21.73 (19.56–23.91) 22.60 (20.46–24.74) 
  Third quartile 29.22 (28.66–29.79) 28.86 (27.58–30.15) 29.14 (27.92–30.36) 29.48 (28.10–30.87) 28.87 (27.84–29.89) 29.88 (27.76–32.00) 30.44 (28.21–32.66) 
  Highest quartile 30.70 (29.92–31.47) 29.89 (28.07–31.72) 27.61 (26.15–29.07) 30.43 (28.67–32.19) 31.74 (30.24–33.23) 34.96 (31.45–38.46) 33.60 (29.76–37.44) 

BMI, body mass index; CI, confidence interval; KNHANES, Korea National Health and Nutrition Examination Survey.

*According to the Asian-Pacific guidelines, the BMI is divided into four groups: underweight (<18.5 kg/m2), normal (18.5–22.9 kg/m2), overweight (23–24.9 kg/m2), and obese (≥25 kg/m2).

Table 2 and online supplementary Table S1 (for all online suppl. material, see https://doi.org/10.1159/000535666) present the weighted overall and age-stratified proportions of AD from 2007 to 2021 by analyzing subgroup and stratification analyses, respectively. During 15 years, the prevalence of AD is stable in the overall population from 2.61% (95% CI, 2.29–2.93) in 2007–2009 to 2.15% (95% CI, 1.68–2.63) in 2020 and 2.38% (95% CI, 1.81–2.95) in 2021 (Table 2; online suppl. Table S1; Fig. 2). Subgroup analysis revealed that the weighted prevalence of AD in adults aged 40–59 years decreased from 1.92% (95% CI, 1.50–2.34) in 2007–2009 to 1.12% (95% CI, 0.87–1.37) in 2016–2019 during the pre-pandemic era (β, −2.506 [95% CI, −4.005 to −1.007]). However, the prevalence of AD in adults aged above 60 years old significantly decreased during the pandemic (β, −3.056 [95% CI, −5.415 to −0.698]) and showed a significant decline (βdiff, −3.934 [95% CI, −6.685 to −1.183]).

Table 2.

National trends of the prevalence of AD and trends of β in age-stratified Korean adults between pre-pandemic and during the pandemic, weighted % (95% CI), in the data gathered from the KNHANES

YearPre-pandemicDuring the pandemicTrends in the pre-pandemic era, β (95% CI)Trends in the pandemic era, β (95% CI)βdiff between 2007–2019 and 2019–2021 (95% CI)
2007–20092010–20122013–20152016–201920202021
Overall 2.61 (2.29–2.93) 1.74 (1.47–2.01) 1.94 (1.66–2.21) 2.24 (1.99–2.48) 2.15 (1.68–2.63) 2.38 (1.81–2.95) −0.857 (−2.113 to 0.399) 0.704 (−2.386 to 3.795) 1.562 (−1.774 to 4.897) 
Subgroup analysis 
 Adults (20–39 years) 3.88 (3.29–4.47) 3.03 (2.45–3.62) 3.73 (3.10–4.35) 4.14 (3.57–4.72) 3.96 (2.92–5.00) 5.07 (3.54–6.61) 1.411 (−1.194 to 4.016) 4.625 (−3.446 to 12.696) 3.214 (−5.267 to 11.695) 
 Adults (40–59 years) 1.92 (1.50–2.34) 0.99 (0.67–1.31) 0.77 (0.50–1.04) 1.12 (0.87–1.37) 1.32 (0.60–2.04) 1.22 (0.62–1.81) 2.506 (4.005 to 1.007) 0.483 (−2.692 to 3.658) 2.988 (−0.523 to 6.499) 
 Adults (≥60 years) 1.14 (0.80–1.48) 0.65 (0.41–0.89) 0.94 (0.64–1.24) 1.27 (0.96–1.58) 0.90 (0.44–1.36) 0.66 (0.30–1.02) 0.878 (−0.538 to 2.294) −3.056 (−5.415 to 0.698) −3.934 (−6.685 to 1.183) 
Stratification analysis 
 Adults (20–39 years) 
  Male 4.08 (3.24–4.92) 2.88 (2.05–3.70) 3.88 (2.93–4.83) 3.40 (2.64–4.17) 3.28 (1.97–4.58) 4.58 (2.61–6.56) −1.098 (−4.723 to 2.527) 5.867 (−4.546 to 16.279) 6.965 (−4.061 to 17.990) 
  Female 3.66 (2.87–4.46) 3.20 (2.42–3.98) 3.56 (2.76–4.37) 4.95 (4.10–5.81) 4.73 (3.07–6.38) 5.61 (3.60–7.62) 4.128 (0.470 to 7.785) 3.264 (−7.703 to 14.231) −0.864 (−12.424 to 10.697) 
  Urban 4.03 (3.39–4.67) 2.85 (2.25–3.46) 3.77 (3.10–4.45) 4.25 (3.64–4.86) 4.29 (3.11–5.48) 4.96 (3.41–6.51) 1.524 (−1.280 to 4.328) 3.542 (−4.754 to 11.838) 2.018 (−6.739 to 10.775) 
  Rural 2.93 (1.56–4.31) 4.22 (2.29–6.14) 3.42 (1.72–5.13) 3.25 (1.69–4.80) 1.65 (0.05–3.24) 6.18 (0.00–12.37) 0.419 (−6.332 to 7.170) 13.656 (−16.795 to 44.106) 13.236 (−17.953 to 44.426) 
  High school or lower education 3.17 (2.22–4.11) 2.38 (1.44–3.33) 3.59 (2.29–4.89) 3.50 (2.32–4.68) 3.31 (1.12–5.50) 3.84 (1.22–6.47) 1.790 (−3.047 to 6.628) 1.701 (−12.528 to 15.930) −0.090 (−15.119 to 14.939) 
  College or higher education 4.26 (3.51–5.01) 3.29 (2.59–3.99) 3.77 (3.07–4.47) 4.28 (3.65–4.92) 4.10 (2.89–5.32) 5.35 (3.65–7.04) 0.691 (−2.398 to 3.780) 5.292 (−3.567 to 14.152) 4.601 (−4.782 to 13.984) 
  Household income (lowest and second quartile) 3.70 (2.68–4.71) 2.88 (1.84–3.92) 3.55 (2.49–4.62) 4.54 (3.45–5.62) 3.54 (1.92–5.15) 4.91 (2.26–7.55) 3.107 (−1.589 to 7.803) 1.329 (−12.534 to 15.192) −1.778 (−16.415 to 12.859) 
  Household income (third and highest quartile) 3.97 (3.25–4.70) 3.12 (2.41–3.83) 3.81 (3.04–4.58) 3.95 (3.31–4.59) 4.13 (2.87–5.39) 5.13 (3.29–6.97) 0.547 (−2.543 to 3.637) 5.950 (−3.615 to 15.514) 5.403 (−4.648 to 15.454) 
 Adults (40–59 years) 
  Male 2.07 (1.40–2.73) 1.02 (0.49–1.56) 0.97 (0.49–1.45) 1.31 (0.89–1.72) 1.27 (0.43–2.11) 1.45 (0.54–2.35) −2.217 (−4.643 to 0.209) 0.720 (−4.149 to 5.590) 2.937 (−2.503 to 8.378) 
  Female 1.78 (1.29–2.26) 0.96 (0.60–1.32) 0.58 (0.31–0.84) 0.94 (0.64–1.23) 1.37 (0.53–2.22) 0.98 (0.15–1.81) −2.782 (−4.507 to 1.057) 0.236 (−4.054 to 4.527) 3.018 (−1.606 to 7.643) 
  Urban 1.96 (1.47–2.44) 1.05 (0.68–1.42) 0.69 (0.40–0.99) 1.23 (0.95–1.52) 1.35 (0.54–2.17) 1.10 (0.47–1.73) −2.335 (−4.062 to 0.607) −0.658 (−4.060 to 2.743) 1.676 (−2.138 to 5.491) 
  Rural 1.78 (0.98–2.59) 0.76 (0.19–1.33) 1.15 (0.47–1.82) 0.46 (0.11–0.80) 1.11 (0.00–2.30) 1.86 (0.21–3.50) −3.579 (−6.397 to 0.761) 7.010 (−1.333 to 15.354) 10.589 (1.783 to 19.396) 
  High school or lower education 1.74 (1.30–2.18) 1.03 (0.65–1.41) 0.67 (0.36–0.98) 0.73 (0.47–0.99) 0.58 (0.11–1.05) 1.35 (0.44–2.25) −3.478 (−5.109 to 1.846) 2.990 (−1.576 to 7.557) 6.468 (1.619 to 11.317) 
  College or higher education 2.41 (1.55–3.26) 0.90 (0.37–1.43) 0.93 (0.44–1.42) 1.56 (1.12–1.99) 1.95 (0.70–3.20) 1.10 (0.34–1.87) −1.620 (−4.403 to 1.162) −2.399 (−6.808 to 2.010) −0.779 (−5.992 to 4.435) 
  Household income (lowest and second quartile) 1.80 (1.18–2.43) 1.57 (0.87–2.27) 1.01 (0.46–1.57) 0.92 (0.53–1.31) 0.95 (0.25–1.66) 2.45 (0.80–4.10) −3.214 (−5.602 to 0.825) 7.572 (−0.667 to 15.811) 10.786 (2.207 to 19.364) 
  Household income (third and highest quartile) 1.98 (1.44–2.52) 0.65 (0.35–0.96) 0.65 (0.34–0.95) 1.20 (0.90–1.51) 1.45 (0.50–2.41) 0.73 (0.20–1.25) −2.116 (−3.990 to 0.243) −2.377 (−5.373 to 0.619) −0.261 (−3.795 to 3.273) 
 Adults (≥60 years) 
  Male 0.99 (0.58–1.40) 0.89 (0.46–1.31) 0.88 (0.45–1.32) 1.42 (0.90–1.95) 0.94 (0.31–1.57) 0.90 (0.27–1.52) 1.484 (−0.670 to 3.638) −2.574 (−6.648 to 1.501) −4.058 (−8.667 to 0.551) 
  Female 1.26 (0.78–1.74) 0.47 (0.20–0.74) 0.98 (0.57–1.40) 1.15 (0.77–1.53) 0.86 (0.29–1.44) 0.45 (0.13–0.77) 0.391 (−1.474 to 2.255) −3.498 (−6.009 to 0.987) −3.889 (−7.017 to 0.762) 
  Urban 1.26 (0.82–1.70) 0.60 (0.32–0.88) 1.01 (0.66–1.37) 1.10 (0.77–1.44) 1.00 (0.44–1.55) 0.66 (0.22–1.11) 0.149 (1.534 to 1.832) −2.215 (−4.983 to 0.553) −2.364 (−5.603 to 0.875) 
  Rural 0.89 (0.36–1.43) 0.76 (0.30–1.22) 0.71 (0.19–1.23) 1.88 (1.13–2.63) 0.54 (0.00–1.08) 0.64 (0.10–1.18) 2.978 (0.102–5.853) −5.916 (10.495 to 1.337) −8.894 (14.301 to 3.487) 
  High school or lower education 1.19 (0.82–1.55) 0.59 (0.35–0.84) 0.88 (0.57–1.19) 1.39 (1.05–1.74) 0.99 (0.46–1.53) 0.61 (0.23–1.00) 1.129 (−0.421 to 2.679) 3.883 (6.467 to 1.300) 5.012 (8.025 to 1.999) 
  College or higher education 0.61 (0.00–1.39) 1.30 (0.31–2.29) 1.38 (0.29–2.46) 0.59 (0.10–1.09) 0.43 (0.00–1.04) 0.84 (0.00–1.81) −0.958 (−3.946 to 2.030) 1.414 (−4.152 to 6.980) 2.372 (−3.945 to 8.689) 
  Household income (lowest and second quartile) 1.20 (0.80–1.61) 0.66 (0.35–0.96) 0.94 (0.57–1.31) 1.33 (0.95–1.72) 1.28 (0.55–2.01) 0.74 (0.25–1.22) 0.852 (−0.893 to 2.596) −3.008 (−6.086 to 0.071) 3.859 (7.398 to 0.321) 
  Household income (third and highest quartile) 0.98 (0.45–1.52) 0.63 (0.29–0.97) 0.94 (0.42–1.46) 1.15 (0.63–1.68) 0.37 (0.00–0.83) 0.54 (0.01–1.08) 1.017 (−1.330 to 3.363) −2.817 (−6.570 to 0.935) −3.834 (−8.259 to 0.592) 
YearPre-pandemicDuring the pandemicTrends in the pre-pandemic era, β (95% CI)Trends in the pandemic era, β (95% CI)βdiff between 2007–2019 and 2019–2021 (95% CI)
2007–20092010–20122013–20152016–201920202021
Overall 2.61 (2.29–2.93) 1.74 (1.47–2.01) 1.94 (1.66–2.21) 2.24 (1.99–2.48) 2.15 (1.68–2.63) 2.38 (1.81–2.95) −0.857 (−2.113 to 0.399) 0.704 (−2.386 to 3.795) 1.562 (−1.774 to 4.897) 
Subgroup analysis 
 Adults (20–39 years) 3.88 (3.29–4.47) 3.03 (2.45–3.62) 3.73 (3.10–4.35) 4.14 (3.57–4.72) 3.96 (2.92–5.00) 5.07 (3.54–6.61) 1.411 (−1.194 to 4.016) 4.625 (−3.446 to 12.696) 3.214 (−5.267 to 11.695) 
 Adults (40–59 years) 1.92 (1.50–2.34) 0.99 (0.67–1.31) 0.77 (0.50–1.04) 1.12 (0.87–1.37) 1.32 (0.60–2.04) 1.22 (0.62–1.81) 2.506 (4.005 to 1.007) 0.483 (−2.692 to 3.658) 2.988 (−0.523 to 6.499) 
 Adults (≥60 years) 1.14 (0.80–1.48) 0.65 (0.41–0.89) 0.94 (0.64–1.24) 1.27 (0.96–1.58) 0.90 (0.44–1.36) 0.66 (0.30–1.02) 0.878 (−0.538 to 2.294) −3.056 (−5.415 to 0.698) −3.934 (−6.685 to 1.183) 
Stratification analysis 
 Adults (20–39 years) 
  Male 4.08 (3.24–4.92) 2.88 (2.05–3.70) 3.88 (2.93–4.83) 3.40 (2.64–4.17) 3.28 (1.97–4.58) 4.58 (2.61–6.56) −1.098 (−4.723 to 2.527) 5.867 (−4.546 to 16.279) 6.965 (−4.061 to 17.990) 
  Female 3.66 (2.87–4.46) 3.20 (2.42–3.98) 3.56 (2.76–4.37) 4.95 (4.10–5.81) 4.73 (3.07–6.38) 5.61 (3.60–7.62) 4.128 (0.470 to 7.785) 3.264 (−7.703 to 14.231) −0.864 (−12.424 to 10.697) 
  Urban 4.03 (3.39–4.67) 2.85 (2.25–3.46) 3.77 (3.10–4.45) 4.25 (3.64–4.86) 4.29 (3.11–5.48) 4.96 (3.41–6.51) 1.524 (−1.280 to 4.328) 3.542 (−4.754 to 11.838) 2.018 (−6.739 to 10.775) 
  Rural 2.93 (1.56–4.31) 4.22 (2.29–6.14) 3.42 (1.72–5.13) 3.25 (1.69–4.80) 1.65 (0.05–3.24) 6.18 (0.00–12.37) 0.419 (−6.332 to 7.170) 13.656 (−16.795 to 44.106) 13.236 (−17.953 to 44.426) 
  High school or lower education 3.17 (2.22–4.11) 2.38 (1.44–3.33) 3.59 (2.29–4.89) 3.50 (2.32–4.68) 3.31 (1.12–5.50) 3.84 (1.22–6.47) 1.790 (−3.047 to 6.628) 1.701 (−12.528 to 15.930) −0.090 (−15.119 to 14.939) 
  College or higher education 4.26 (3.51–5.01) 3.29 (2.59–3.99) 3.77 (3.07–4.47) 4.28 (3.65–4.92) 4.10 (2.89–5.32) 5.35 (3.65–7.04) 0.691 (−2.398 to 3.780) 5.292 (−3.567 to 14.152) 4.601 (−4.782 to 13.984) 
  Household income (lowest and second quartile) 3.70 (2.68–4.71) 2.88 (1.84–3.92) 3.55 (2.49–4.62) 4.54 (3.45–5.62) 3.54 (1.92–5.15) 4.91 (2.26–7.55) 3.107 (−1.589 to 7.803) 1.329 (−12.534 to 15.192) −1.778 (−16.415 to 12.859) 
  Household income (third and highest quartile) 3.97 (3.25–4.70) 3.12 (2.41–3.83) 3.81 (3.04–4.58) 3.95 (3.31–4.59) 4.13 (2.87–5.39) 5.13 (3.29–6.97) 0.547 (−2.543 to 3.637) 5.950 (−3.615 to 15.514) 5.403 (−4.648 to 15.454) 
 Adults (40–59 years) 
  Male 2.07 (1.40–2.73) 1.02 (0.49–1.56) 0.97 (0.49–1.45) 1.31 (0.89–1.72) 1.27 (0.43–2.11) 1.45 (0.54–2.35) −2.217 (−4.643 to 0.209) 0.720 (−4.149 to 5.590) 2.937 (−2.503 to 8.378) 
  Female 1.78 (1.29–2.26) 0.96 (0.60–1.32) 0.58 (0.31–0.84) 0.94 (0.64–1.23) 1.37 (0.53–2.22) 0.98 (0.15–1.81) −2.782 (−4.507 to 1.057) 0.236 (−4.054 to 4.527) 3.018 (−1.606 to 7.643) 
  Urban 1.96 (1.47–2.44) 1.05 (0.68–1.42) 0.69 (0.40–0.99) 1.23 (0.95–1.52) 1.35 (0.54–2.17) 1.10 (0.47–1.73) −2.335 (−4.062 to 0.607) −0.658 (−4.060 to 2.743) 1.676 (−2.138 to 5.491) 
  Rural 1.78 (0.98–2.59) 0.76 (0.19–1.33) 1.15 (0.47–1.82) 0.46 (0.11–0.80) 1.11 (0.00–2.30) 1.86 (0.21–3.50) −3.579 (−6.397 to 0.761) 7.010 (−1.333 to 15.354) 10.589 (1.783 to 19.396) 
  High school or lower education 1.74 (1.30–2.18) 1.03 (0.65–1.41) 0.67 (0.36–0.98) 0.73 (0.47–0.99) 0.58 (0.11–1.05) 1.35 (0.44–2.25) −3.478 (−5.109 to 1.846) 2.990 (−1.576 to 7.557) 6.468 (1.619 to 11.317) 
  College or higher education 2.41 (1.55–3.26) 0.90 (0.37–1.43) 0.93 (0.44–1.42) 1.56 (1.12–1.99) 1.95 (0.70–3.20) 1.10 (0.34–1.87) −1.620 (−4.403 to 1.162) −2.399 (−6.808 to 2.010) −0.779 (−5.992 to 4.435) 
  Household income (lowest and second quartile) 1.80 (1.18–2.43) 1.57 (0.87–2.27) 1.01 (0.46–1.57) 0.92 (0.53–1.31) 0.95 (0.25–1.66) 2.45 (0.80–4.10) −3.214 (−5.602 to 0.825) 7.572 (−0.667 to 15.811) 10.786 (2.207 to 19.364) 
  Household income (third and highest quartile) 1.98 (1.44–2.52) 0.65 (0.35–0.96) 0.65 (0.34–0.95) 1.20 (0.90–1.51) 1.45 (0.50–2.41) 0.73 (0.20–1.25) −2.116 (−3.990 to 0.243) −2.377 (−5.373 to 0.619) −0.261 (−3.795 to 3.273) 
 Adults (≥60 years) 
  Male 0.99 (0.58–1.40) 0.89 (0.46–1.31) 0.88 (0.45–1.32) 1.42 (0.90–1.95) 0.94 (0.31–1.57) 0.90 (0.27–1.52) 1.484 (−0.670 to 3.638) −2.574 (−6.648 to 1.501) −4.058 (−8.667 to 0.551) 
  Female 1.26 (0.78–1.74) 0.47 (0.20–0.74) 0.98 (0.57–1.40) 1.15 (0.77–1.53) 0.86 (0.29–1.44) 0.45 (0.13–0.77) 0.391 (−1.474 to 2.255) −3.498 (−6.009 to 0.987) −3.889 (−7.017 to 0.762) 
  Urban 1.26 (0.82–1.70) 0.60 (0.32–0.88) 1.01 (0.66–1.37) 1.10 (0.77–1.44) 1.00 (0.44–1.55) 0.66 (0.22–1.11) 0.149 (1.534 to 1.832) −2.215 (−4.983 to 0.553) −2.364 (−5.603 to 0.875) 
  Rural 0.89 (0.36–1.43) 0.76 (0.30–1.22) 0.71 (0.19–1.23) 1.88 (1.13–2.63) 0.54 (0.00–1.08) 0.64 (0.10–1.18) 2.978 (0.102–5.853) −5.916 (10.495 to 1.337) −8.894 (14.301 to 3.487) 
  High school or lower education 1.19 (0.82–1.55) 0.59 (0.35–0.84) 0.88 (0.57–1.19) 1.39 (1.05–1.74) 0.99 (0.46–1.53) 0.61 (0.23–1.00) 1.129 (−0.421 to 2.679) 3.883 (6.467 to 1.300) 5.012 (8.025 to 1.999) 
  College or higher education 0.61 (0.00–1.39) 1.30 (0.31–2.29) 1.38 (0.29–2.46) 0.59 (0.10–1.09) 0.43 (0.00–1.04) 0.84 (0.00–1.81) −0.958 (−3.946 to 2.030) 1.414 (−4.152 to 6.980) 2.372 (−3.945 to 8.689) 
  Household income (lowest and second quartile) 1.20 (0.80–1.61) 0.66 (0.35–0.96) 0.94 (0.57–1.31) 1.33 (0.95–1.72) 1.28 (0.55–2.01) 0.74 (0.25–1.22) 0.852 (−0.893 to 2.596) −3.008 (−6.086 to 0.071) 3.859 (7.398 to 0.321) 
  Household income (third and highest quartile) 0.98 (0.45–1.52) 0.63 (0.29–0.97) 0.94 (0.42–1.46) 1.15 (0.63–1.68) 0.37 (0.00–0.83) 0.54 (0.01–1.08) 1.017 (−1.330 to 3.363) −2.817 (−6.570 to 0.935) −3.834 (−8.259 to 0.592) 

CI, confidence interval; KNHANES, Korea National Health and Nutrition Examination Survey.

Numbers in bold indicate a signifcant difference (p< 0.05).

Fig. 2.

15-year trends in the prevalence of AD in age-stratified Korean adults, 2007–2021.

Fig. 2.

15-year trends in the prevalence of AD in age-stratified Korean adults, 2007–2021.

Close modal

From age-stratification analysis, the adults aged 40–59 years showed a significant increase after the pandemic outbreak was evident in specific variables: individuals with rural residence, lower education, and lower household income quartiles (Table 2; rural residence: βdiff, 10.589 [95% CI, 1.783–19.396]; high school or lower education: βdiff, 6.468 [95% CI, 1.619–11.317]; and lowest and second income quartiles: βdiff, 10.786 [95% CI, 2.207–19.364]). Interestingly, adults aged 60 years and older showed a significant decrease in the slope after the outbreak was evident in specific variables: individuals with female sex, rural residence, lower education, and lower household income quartiles (Table 2; female sex: βdiff, −3.889 [95% CI, −7.017 to −0.762]; rural residence: βdiff, −8.894 [95% CI, −14.301 to −3.487]; high school or lower education: βdiff, −5.012 [95% CI, −8.025 to −1.999]; and lowest and second income quartiles: βdiff, −3.859 [95% CI, −7.398 to −0.321]). No distinct pandemic-related vulnerable factors associated with AD were identified in both age-stratified and crude populations (Table 3; online suppl. Table S2).

Table 3.

Weighted ORs of pre-pandemic and during the pandemic, ORs (95% CI), in the data gathered from the KNHANES

2010–2012 versus 2007–2009 (reference)p value2013–2015 versus 2010–2012 (reference)p value2016–2019 versus 2013–2015 (reference)p value2020 versus 2016–2019 (reference)p value2021 versus 2020 (reference)p value
Overall 
 Adults (20–39 years) 0.78 (0.60–0.99) 0.048 1.24 (0.95–1.61) 0.112 1.12 (0.89–1.40) 0.340 0.95 (0.70–1.30) 0.768 1.30 (0.86–1.96) 0.219 
 Adults (40–59 years) 0.51 (0.35–0.76) 0.001 0.77 (0.48–1.25) 0.295 1.46 (0.96–2.22) 0.074 1.18 (0.66–2.13) 0.580 0.92 (0.44–1.91) 0.822 
 Adults (≥60 years) 0.57 (0.35–0.91) 0.019 1.45 (0.89–2.36) 0.134 1.36 (0.91–2.03) 0.136 0.71 (0.39–1.27) 0.245 0.73 (0.34–1.58) 0.422 
Male 
 Adults (20–39 years) 0.70 (0.48–1.01) 0.051 1.37 (0.93–2.01) 0.117 0.87 (0.62–1.23) 0.436 0.96 (0.60–1.54) 0.869 1.42 (0.78–2.58) 0.252 
 Adults (40–59 years) 0.49 (0.26–0.91) 0.025 0.95 (0.46–1.95) 0.878 1.35 (0.75–2.45) 0.316 0.97 (0.47–2.02) 0.938 1.15 (0.47–2.82) 0.767 
 Adults (≥60 years) 0.89 (0.47–1.70) 0.727 1.00 (0.50–2.00) 1.000 1.62 (0.87–3.00) 0.126 0.66 (0.30–1.46) 0.302 0.95 (0.36–2.55) 0.921 
Female 
 Adults (20–39 years) 0.87 (0.62–1.22) 0.412 1.12 (0.79–1.58) 0.524 1.41 (1.05–1.90) 0.023 0.95 (0.63–1.43) 0.811 1.20 (0.71–2.03) 0.500 
 Adults (40–59 years) 0.53 (0.33–0.85) 0.009 0.60 (0.33–1.09) 0.092 1.63 (0.94–2.84) 0.084 1.47 (0.74–2.95) 0.273 0.71 (0.25–2.02) 0.520 
 Adults (≥60 years) 0.37 (0.19–0.74) 0.005 2.11 (1.03–4.31) 0.041 1.17 (0.68–2.01) 0.571 0.75 (0.35–1.61) 0.462 0.52 (0.19–1.41) 0.199 
Urban 
 Adults (20–39 years) 0.70 (0.53–0.92) 0.011 1.34 (1.01–1.78) 0.048 1.13 (0.89–1.44) 0.308 1.01 (0.73–1.39) 0.948 1.16 (0.76–1.79) 0.490 
 Adults (40–59 years) 0.53 (0.34–0.82) 0.005 0.66 (0.38–1.15) 0.138 1.79 (1.10–2.91) 0.019 1.10 (0.58–2.09) 0.774 0.81 (0.36–1.85) 0.617 
 Adults (≥60 years) 0.47 (0.26–0.85) 0.012 1.70 (0.95–3.06) 0.076 1.09 (0.68–1.74) 0.724 0.90 (0.46–1.76) 0.766 0.66 (0.27–1.62) 0.366 
Rural 
 Adults (20–39 years) 1.46 (0.74–2.87) 0.277 0.81 (0.40–1.62) 0.544 0.95 (0.46–1.93) 0.881 0.50 (0.16–1.51) 0.218 3.94 (0.95–16.39) 0.060 
 Adults (40–59 years) 0.42 (0.18–1.02) 0.054 1.52 (0.58–3.95) 0.395 0.40 (0.15–1.04) 0.059 2.44 (0.65–9.10) 0.185 1.69 (0.42–6.81) 0.458 
 Adults (≥60 years) 0.85 (0.36–1.99) 0.703 0.94 (0.36–2.44) 0.900 2.66 (1.15–6.16) 0.022 0.28 (0.09–0.85) 0.025 1.20 (0.31–4.57) 0.791 
Education (high school or lower education) 
 Adults (20–39 years) 0.75 (0.45–1.24) 0.260 1.53 (0.88–2.65) 0.133 0.97 (0.58–1.63) 0.919 0.95 (0.44–2.04) 0.885 1.17 (0.44–3.10) 0.759 
 Adults (40–59 years) 0.59 (0.38–0.92) 0.021 0.65 (0.36–1.18) 0.155 1.08 (0.60–1.94) 0.792 0.79 (0.33–1.92) 0.606 2.35 (0.82–6.75) 0.112 
 Adults (≥60 years) 0.50 (0.30–0.83) 0.008 1.50 (0.87–2.58) 0.146 1.58 (1.03–2.45) 0.038 0.71 (0.38–1.33) 0.285 0.62 (0.26–1.45) 0.265 
Education (college or higher education) 
 Adults (20–39 years) 0.77 (0.58–1.02) 0.067 1.15 (0.86–1.54) 0.351 1.14 (0.89–1.46) 0.289 0.96 (0.68–1.35) 0.800 1.32 (0.85–2.06) 0.222 
 Adults (40–59 years) 0.37 (0.18–0.74) 0.005 1.03 (0.46–2.30) 0.934 1.69 (0.92–3.09) 0.090 1.26 (0.62–2.55) 0.522 0.56 (0.22–1.44) 0.228 
 Adults (≥60 years) 2.13 (0.49–9.35) 0.316 1.06 (0.35–3.21) 0.919 0.43 (0.14–1.36) 0.151 0.72 (0.14–3.70) 0.698 1.96 (0.32–12.03) 0.464 
Household income (lowest-second quartile) 
 Adults (20–39 years) 0.77 (0.48–1.23) 0.280 1.24 (0.77–2.02) 0.378 1.29 (0.86–1.92) 0.213 0.77 (0.45–1.33) 0.352 1.41 (0.67–2.95) 0.365 
 Adults (40–59 years) 0.87 (0.49–1.54) 0.628 0.64 (0.32–1.31) 0.223 0.91 (0.45–1.83) 0.791 1.03 (0.44–2.42) 0.940 2.61 (0.95–7.15) 0.063 
 Adults (≥60 years) 0.54 (0.30–0.97) 0.038 1.44 (0.78–2.65) 0.247 1.42 (0.87–2.33) 0.159 0.96 (0.49–1.87) 0.900 0.57 (0.23–1.41) 0.226 
Household income (third-highest quartile) 
 Adults (20–39 years) 0.78 (0.58–1.05) 0.102 1.23 (0.90–1.68) 0.197 1.04 (0.79–1.36) 0.784 1.05 (0.73–1.50) 0.800 1.26 (0.77–2.04) 0.356 
 Adults (40–59 years) 0.33 (0.19–0.56) <0.001 0.99 (0.51–1.92) 0.970 1.87 (1.09–3.20) 0.022 1.21 (0.60–2.46) 0.591 0.50 (0.19–1.31) 0.156 
 Adults (≥60 years) 0.64 (0.29–1.39) 0.260 1.49 (0.68–3.26) 0.315 1.23 (0.60–2.54) 0.573 0.32 (0.09–1.17) 0.086 1.46 (0.30–6.99) 0.637 
2010–2012 versus 2007–2009 (reference)p value2013–2015 versus 2010–2012 (reference)p value2016–2019 versus 2013–2015 (reference)p value2020 versus 2016–2019 (reference)p value2021 versus 2020 (reference)p value
Overall 
 Adults (20–39 years) 0.78 (0.60–0.99) 0.048 1.24 (0.95–1.61) 0.112 1.12 (0.89–1.40) 0.340 0.95 (0.70–1.30) 0.768 1.30 (0.86–1.96) 0.219 
 Adults (40–59 years) 0.51 (0.35–0.76) 0.001 0.77 (0.48–1.25) 0.295 1.46 (0.96–2.22) 0.074 1.18 (0.66–2.13) 0.580 0.92 (0.44–1.91) 0.822 
 Adults (≥60 years) 0.57 (0.35–0.91) 0.019 1.45 (0.89–2.36) 0.134 1.36 (0.91–2.03) 0.136 0.71 (0.39–1.27) 0.245 0.73 (0.34–1.58) 0.422 
Male 
 Adults (20–39 years) 0.70 (0.48–1.01) 0.051 1.37 (0.93–2.01) 0.117 0.87 (0.62–1.23) 0.436 0.96 (0.60–1.54) 0.869 1.42 (0.78–2.58) 0.252 
 Adults (40–59 years) 0.49 (0.26–0.91) 0.025 0.95 (0.46–1.95) 0.878 1.35 (0.75–2.45) 0.316 0.97 (0.47–2.02) 0.938 1.15 (0.47–2.82) 0.767 
 Adults (≥60 years) 0.89 (0.47–1.70) 0.727 1.00 (0.50–2.00) 1.000 1.62 (0.87–3.00) 0.126 0.66 (0.30–1.46) 0.302 0.95 (0.36–2.55) 0.921 
Female 
 Adults (20–39 years) 0.87 (0.62–1.22) 0.412 1.12 (0.79–1.58) 0.524 1.41 (1.05–1.90) 0.023 0.95 (0.63–1.43) 0.811 1.20 (0.71–2.03) 0.500 
 Adults (40–59 years) 0.53 (0.33–0.85) 0.009 0.60 (0.33–1.09) 0.092 1.63 (0.94–2.84) 0.084 1.47 (0.74–2.95) 0.273 0.71 (0.25–2.02) 0.520 
 Adults (≥60 years) 0.37 (0.19–0.74) 0.005 2.11 (1.03–4.31) 0.041 1.17 (0.68–2.01) 0.571 0.75 (0.35–1.61) 0.462 0.52 (0.19–1.41) 0.199 
Urban 
 Adults (20–39 years) 0.70 (0.53–0.92) 0.011 1.34 (1.01–1.78) 0.048 1.13 (0.89–1.44) 0.308 1.01 (0.73–1.39) 0.948 1.16 (0.76–1.79) 0.490 
 Adults (40–59 years) 0.53 (0.34–0.82) 0.005 0.66 (0.38–1.15) 0.138 1.79 (1.10–2.91) 0.019 1.10 (0.58–2.09) 0.774 0.81 (0.36–1.85) 0.617 
 Adults (≥60 years) 0.47 (0.26–0.85) 0.012 1.70 (0.95–3.06) 0.076 1.09 (0.68–1.74) 0.724 0.90 (0.46–1.76) 0.766 0.66 (0.27–1.62) 0.366 
Rural 
 Adults (20–39 years) 1.46 (0.74–2.87) 0.277 0.81 (0.40–1.62) 0.544 0.95 (0.46–1.93) 0.881 0.50 (0.16–1.51) 0.218 3.94 (0.95–16.39) 0.060 
 Adults (40–59 years) 0.42 (0.18–1.02) 0.054 1.52 (0.58–3.95) 0.395 0.40 (0.15–1.04) 0.059 2.44 (0.65–9.10) 0.185 1.69 (0.42–6.81) 0.458 
 Adults (≥60 years) 0.85 (0.36–1.99) 0.703 0.94 (0.36–2.44) 0.900 2.66 (1.15–6.16) 0.022 0.28 (0.09–0.85) 0.025 1.20 (0.31–4.57) 0.791 
Education (high school or lower education) 
 Adults (20–39 years) 0.75 (0.45–1.24) 0.260 1.53 (0.88–2.65) 0.133 0.97 (0.58–1.63) 0.919 0.95 (0.44–2.04) 0.885 1.17 (0.44–3.10) 0.759 
 Adults (40–59 years) 0.59 (0.38–0.92) 0.021 0.65 (0.36–1.18) 0.155 1.08 (0.60–1.94) 0.792 0.79 (0.33–1.92) 0.606 2.35 (0.82–6.75) 0.112 
 Adults (≥60 years) 0.50 (0.30–0.83) 0.008 1.50 (0.87–2.58) 0.146 1.58 (1.03–2.45) 0.038 0.71 (0.38–1.33) 0.285 0.62 (0.26–1.45) 0.265 
Education (college or higher education) 
 Adults (20–39 years) 0.77 (0.58–1.02) 0.067 1.15 (0.86–1.54) 0.351 1.14 (0.89–1.46) 0.289 0.96 (0.68–1.35) 0.800 1.32 (0.85–2.06) 0.222 
 Adults (40–59 years) 0.37 (0.18–0.74) 0.005 1.03 (0.46–2.30) 0.934 1.69 (0.92–3.09) 0.090 1.26 (0.62–2.55) 0.522 0.56 (0.22–1.44) 0.228 
 Adults (≥60 years) 2.13 (0.49–9.35) 0.316 1.06 (0.35–3.21) 0.919 0.43 (0.14–1.36) 0.151 0.72 (0.14–3.70) 0.698 1.96 (0.32–12.03) 0.464 
Household income (lowest-second quartile) 
 Adults (20–39 years) 0.77 (0.48–1.23) 0.280 1.24 (0.77–2.02) 0.378 1.29 (0.86–1.92) 0.213 0.77 (0.45–1.33) 0.352 1.41 (0.67–2.95) 0.365 
 Adults (40–59 years) 0.87 (0.49–1.54) 0.628 0.64 (0.32–1.31) 0.223 0.91 (0.45–1.83) 0.791 1.03 (0.44–2.42) 0.940 2.61 (0.95–7.15) 0.063 
 Adults (≥60 years) 0.54 (0.30–0.97) 0.038 1.44 (0.78–2.65) 0.247 1.42 (0.87–2.33) 0.159 0.96 (0.49–1.87) 0.900 0.57 (0.23–1.41) 0.226 
Household income (third-highest quartile) 
 Adults (20–39 years) 0.78 (0.58–1.05) 0.102 1.23 (0.90–1.68) 0.197 1.04 (0.79–1.36) 0.784 1.05 (0.73–1.50) 0.800 1.26 (0.77–2.04) 0.356 
 Adults (40–59 years) 0.33 (0.19–0.56) <0.001 0.99 (0.51–1.92) 0.970 1.87 (1.09–3.20) 0.022 1.21 (0.60–2.46) 0.591 0.50 (0.19–1.31) 0.156 
 Adults (≥60 years) 0.64 (0.29–1.39) 0.260 1.49 (0.68–3.26) 0.315 1.23 (0.60–2.54) 0.573 0.32 (0.09–1.17) 0.086 1.46 (0.30–6.99) 0.637 

CI, confidence interval; KNHANES, Korea National Health and Nutrition Examination Survey; OR, odds ratio.

Numbers in bold indicate a signifcant difference (p< 0.05).

Findings and Explanation

We investigated the national trends and age-stratified prevalence for AD among adults from 2007 to 2021, focusing mainly on trends between pre-pandemic and pandemic eras, and obtained several main findings. First, to the best of our knowledge, this is the first large-scale, long-term serial cross-sectional study to examine the trends for AD. The overall trends of AD remained stable, and the prevalence of younger adults was higher than older adults during the 15-year observation period. Second, adults aged 40–59 years showed a significant decrease in the prevalence of AD in the pre-pandemic era, but this trend disappeared after the outbreak. Third, adults aged 60 years and older had a stable trend in the prevalence of AD before the pandemic but have seen a significant decline after the onset of the pandemic. Fourth, from age-stratification analysis, the adults aged 40–59 years showed a significant increase after the pandemic outbreak was evident in individuals with lower socioeconomic factors, including rural residence, lower education, and lower household income. Fifth, adults aged 60 years and older showed a significant decrease in the slope after the outbreak was evident in low-resource populations such as individuals with rural residence, lower education, and lower household income quartiles.

Possible Mechanisms

The prevalence of AD remained stable at less than 3% in the overall population from 2007 to 2021. In a previous study about the prevalence of AD in 16 countries, the prevalence of AD in adults ranged from 3.4$ in Israel to 33.7% in Thailand, suggesting that the prevalence of AD in adults in South Korea was relatively low [19]. In addition, the 15-year overall prevalence of AD was higher in younger adults compared to older adults. AD can be challenging to diagnose and treat in older populations due to the traditional misconception that it is a “pediatric disease,” under-reporting behaviors, age-specific immune responses, and different clinical phenotypes and lifestyle factors [1]. This has been reflected in the relatively lower prevalence of AD in older populations.

The pre-pandemic prevalence of AD in adults aged 40–59 years decreased significantly. This is likely due to gradually improved healthcare access, early diagnosis, effective management strategies during the pre-pandemic prevalence, and healthcare-seeking behavior among people in this middle-aged group [1]. One previous study suggested an association between severe acute respiratory syndrome coronavirus 2 infection and risk for AD in adults [20]. In addition, infection for severe acute respiratory syndrome coronavirus 2 during the pandemic altered immune systems, leading to more vulnerable conditions for AD [21]. Therefore, the impact of the COVID-19 pandemic may have stalled the decreasing trends of AD during the outbreak.

Adults aged 60 years and older had a stable trend in the prevalence of AD before the pandemic but have seen a significant decline after the onset of the pandemic. During the pandemic, these reductions were likely related to reduced healthcare access and reluctance to visit the hospital during the pandemic [22]. In addition, the decrease in the prevalence of AD could be interpreted as a result of the pandemic-related policies, including restricted business hours, self-isolation protocols, social distancing rules, mask mandates, and national lockdowns. These policies could prevent and mitigate the transmission of the virus and served as physical barriers and intricate environmental variables that limited both direct and indirect exposure to allergens, potentially contributing to the reduced prevalence of AD [23].

The age-stratified data revealed intriguing patterns in the prevalence of AD among different age groups and socioeconomic status, particularly during the pandemic. For adults aged 40–59 years, the significant increase in AD prevalence among individuals with lower socioeconomic factors during the pandemic may be caused by the prolonged use of personal protective equipment and chronic levels of stress, including economic and psychosocial burdens [24]. In addition, a lower socioeconomic status has been associated with higher disease burden, which increased severity and poorer control of AD on individual levels [25, 26]. Recent advancements in treatment modalities for AD, particularly the rise of biologics and the COVID-19 pandemic crisis, have exacerbated existing health inequalities, which induced the disparities in access and efficacy of these emerging options [1, 27].

Conversely, for adults aged 60 and above, the notable decline in AD prevalence in similar low-resource settings during the pandemic could be attributable to reduced healthcare access, leading to underdiagnosis or higher mortality rates due to AD and associated comorbidities during the pandemic [22]. Therefore, it is crucial to develop policies for considering age-specific subgroups in the pandemic, indicating the need for more personalized, demographic-specific approaches to resolving AD.

Strengths and Limitations

The strength of this study lies in the large-scale, long-term serial cross-sectional study of 83,566 Korean adults. Previous studies have variably reported increasing and decreasing trends in AD prevalence among adults, suggesting inconclusive evidence indicating the need for further study [6‒8, 28]. Moreover, these studies had methodological limitations, including limited sample sizes, shorter durations of follow-up, and predominantly focused on children [6, 9, 10, 28]. However, the present findings should also be interpreted in light of limitations. First, the absence of data on the child/adolescents limits the generalizability of the findings to younger populations, potentially missing essential information on the prevalence of the studied conditions in this population [29]. Second, the COVID-19 pandemic may have led to an underestimation of cases due to the reluctance to visit the hospital [30]. Third, the dependence of the study on self-reported data introduced the possibility of recall and social desirability bias [31]. Fourth, the study involved the South Korean populations, which may limit the generalizability to other ethnic or geographic populations. Fifth, this study makes it difficult to explain the causality and underlying mechanisms between the COVID-19 pandemic and AD; therefore, further studies are needed. Last, we categorized the pre-pandemic years into four groups. As a result, there were differences in participant numbers between pre-pandemic and during the pandemic. To minimize the impact of these differences, we conducted a weighted complex sampling analysis.

During the observation period, the overall prevalence of AD remained stable at approximately 2% during the 15-year observation period. Meanwhile, younger adults exhibited higher prevalence rates than older adults. We explained the impact of the COVID-19 pandemic with significant alterations in the prevalence of AD across different age groups and socioeconomic status. Although adults aged 40–59 years showed gradually decreasing trends in the prevalence of AD during the pre-pandemic, adults aged 60 years and older had significantly decreasing trends during the outbreak. In addition, the COVID-19 pandemic disrupted these trends; there were increasing trends of AD prevalence in adults aged 40–59 years with low socioeconomic status and decreasing trends in those aged 60 years and older. These shifts highlight the urgent need for targeted interventions and suggest that future policies should consider age and socioeconomic factors when addressing AD management, especially in a global health crisis.

The KNHANES data were anonymous and the study protocol was approved by the Korea Disease Control and Prevention Agency (KDCA) and Institutional Review Board of Kyung Hee University (KHUH 2022-06-042). Before their inclusion in the study, all participants provided written informed consent.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT; RS-2023-00248157), Korean Ministry of Food and Drug Safety in 2023 (21153MFDS601), and the Ministry of Science and ICT (NRF-2022R1A2C3009749). The funding agencies had no role in the design and conduct of the study; collection, management, analysis, or interpretation of the data; preparation, review, or approval of the manuscript; and the decision to submit the manuscript for publication.

Dr. Dong Keon Yon had full access to all the data in the study and took responsibility for the integrity of the data and the accuracy of the data analysis conducted by the researchers. All the authors approved the final version of the manuscript before submission. Study concept and design, acquisition, analysis, or interpretation of data, drafting of the manuscript, and statistical analysis: Jiseung Kang, Jaeyu Park, Tae Kim, and Dong Keon Yon; critical revision of the manuscript for important intellectual content: Jiseung Kang, Jaeyu Park, Myeongcheol Lee, Hyeon Jin Kim, Rosie Kwon, Sunyoung Kim, Masoud Rahmati, Ai Koyanagi, Lee Smith, Min Seo Kim, Seong H. Cho, Tae Kim, and Dong Keon Yon; study supervision: Tae Kim and Dong Keon Yon. Jiseung Kang and Jaeyu Park contributed equally. Dong Keon Yon supervised the study and served as a guarantor. The corresponding author attests that all listed authors meet the authorship criteria and that no others meeting the criteria have been omitted.

Additional Information

Jiseung Kang and Jaeyu Park contributed equally to this work.Edited by: H.-U. Simon, Bern.

Data are publicly available on legal and ethical grounds from the Korea Disease Control and Prevention Agency as open data (https://knhanes.kdca.go.kr/knhanes/eng/index.do). Further inquiries including the study protocol and statistical code can be directed to the corresponding author, D.K.Y. (email: yonkkang@gmail.com).

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