Association between Serum Folic Acid Levels and Asthma in the Korean Population: A Study Based on the 2016–2018 Korea National Health and Nutrition Examination Survey

Background: Folic acid is involved in inflammatory reactions; however, the association between folic acid and allergic diseases, particularly asthma, remains unclear. Thus, this study aimed to evaluate the association between serum folic acid levels and asthma in Koreans.Methods: This study analyzed the serum folic acid levels of 6,615 individuals included in the 2016–2018 Korea National Health and Nutrition Examination Survey. The prevalence of asthma was determined using a questionnaire that identified cases of physician-diagnosed asthma. The relationship between serum folic acid levels and asthma was analyzed using logistic regression analysis.Results: Multiple logistic regression analysis showed that a 1 ng/mL increase in serum folic acid level significantly reduced the risk of asthma after adjusting for confounding factors including sex, age, household income, current smoking, current alcohol use, and body mass index (odds ratio [OR], 0.930; 95% confidence interval [CI], 0.876– 0.987; P=0.017). The relationship between the adjusted odds of asthma and serum folic acid levels were consistently inverse (OR, 2.266; 95% CI, 1.126–4.420; P for trend=0.038).Conclusion: Serum folic acid levels are inversely associated with physician-diagnosed asthma in the Korean population.