Mediated relationship between Vitamin D deficiency and reduced pulmonary function by copper in Taiwanese young adults

Background: Vitamin D deficiency is prevalent worldwide and associated with worse outcomes in various lung diseases. This study examines the association between vitamin D deficiency and pulmonary function in healthy young adults. Methods: This prospective cohort study (2017–2019) explored the impact of vitamin D deficiency on pulmonary function in a community-based young adult population. Pulmonary function was assessed via spirometry, with serum 25-hydroxyvitamin D [25(OH)D] and urinary copper levels quantified. Multivariate regression was used to estimate the relationship between vitamin D levels and lung function, with mediation analysis evaluating copper's role. Results: The study included 1034 participants, average age 33.45 years, 41.93 % male. The median 25(OH)D level was 19.20 ng/mL (Interquartile Range: 13.48–24.90 ng/mL). Over half (54.74 %) had 25(OH)D levels below 20 ng/mL. Higher 25(OH)D levels were associated with better forced vital capacity (FVC) and forced expiratory volume in one second (FEV₁). Trends suggested subgroup differences, but these were not statistically significant, indicating a consistent effect of 25(OH)D on pulmonary function across groups. SEM analysis suggested urinary copper as a mediator between 25(OH)D levels and FVC. Conclusion: Vitamin D deficiency is significantly associated with reduced pulmonary function in young adults in Taiwan.