Association of food folate with asthma in US children and adolescents: a cross-sectional study

<b>Background：</b> Asthma is a chronic inflammatory disease. Currently, contradictory findings exist regarding the association between food folate and asthma. Therefore, we hypothesize a positive correlation between food folate and asthma. <b>Purpose</b>： To investigate the possible relationship between food folate intake and the development of asthma in children and adolescents in the United States. <b>Methods：</b> Data from the U.S. National Health and Nutrition Examination Survey (NHANES) from 2009-2018 were analyzed cross-sectionally by covariate adjustment using multivariate logistic regression, restricted triple spline curves, threshold effects, and stratified analyses. <b>Results:</b> There were 8,821 participants, of whom 1,697 (19.2%) self-reported having received a diagnosis of asthma from a physician or other health professional. After accounting for potential confounders, the adjusted odds ratios (ORs) for asthma in the second (T2, 111-178ug/day) and third (T3, &gt;178ug/day) groups were 1.15 (1-1.33) and 1.23 (1.04-1.46), respectively, compared with the group with the lowest food folate intake (T1, &lt;111ug/day). In addition, the association between food folate intake and asthma showed an inverse L-shaped curve (non-linear relationship, p = 0.003), and stratified analysis further validated the robustness of the results. The OR of asthma in subjects with food folate intake less than 263.9ug/day was 1.002 (1.001-1.004). <b>Conclusion:</b> In children and adolescents in the United States, there is a non-linear association (inverted “L” shape) between food folate intake and asthma, with an inflection point at 263.9 micrograms per day.