Association between urinary manganese and pulmonary function in young adults: A cross-sectional design with a longitudinal cohort validation

Background: The impact of heavy metals on pulmonary function among young adults has been scarcely studied, especially by a longitudinal cohort study. Methods: We prospectively enrolled 974 young adults (aged 20-45 years) during 2017-2019 and measured pulmonary function and urinary heavy metals, including manganese, copper, chromium, iron, nickel, zinc, cadmium, and lead. Among them, 461 participants had examination of the same urinary heavy metals during 2006-2008, which could be used as a cohort for long-term effect of urinary metals on pulmonary function. Results: In the 974 enrolled participants, urinary heavy metals were within normal range. The urinary manganese level was the only significant factor for the observed/predicted ratios of forced vital capacity (FVC %)(13 coefficient: -1.217, p = 0.030), forced expiratory volume in one second (FEV1%)(13: -1.664, p < 0.001), and FEV1/ FVC% of predicted (13: -0.598, p = 0.047) in multivariable linear regression under cross sectional design. In cohort analysis, the urinary manganese level was also negatively associated with the FEV1% (13: -1.920, p = 0.021). There was no significance between other urinary heavy metals and pulmonary function for all participants. The urinary manganese significantly negatively correlated with FVC%, FEV1% and FEV1/FVC% in female subgroup whereas copper and iron were significantly negatively correlated with FVC% in male subgroup. Conclusions: Among urinary heavy metals, urinary manganese level was associated with pulmonary function negatively, even the level was within normal range. In addition, women might be more susceptible to manganese. There is emergent need to conduct further investigation to confirm the respiratory hazardous effects of manganese.