Association between Concentrations of Metals in Urine and Adult Asthma: A Case-Control Study in Wuhan, China

Abstract

Background: Several metals have been reported to be associated with childhood asthma. However, the results on relationships between metals and risk of childhood asthma are inconclusive, and the research on adult asthma in the Chinese general population is rare.

Objectives: To investigate potential associations between levels of urinary metals and adult asthma.

Methods: A case-control study of 551 adult asthma cases and 551 gender- and age-matched controls was conducted in Wuhan, China. Demographic information was obtained, and lung function was assessed. The urinary concentrations of 22 metals were measured by inductively coupled plasma mass spectrometry.

Results: After adjusting for other metalsand other covariates, urinary cadmium, molybdenum, chromium, copper, uranium and selenium were positively associated with asthma, with odds ratios (95% CI) of 1.69 (1.00, 2.85), 3.76 (2.30, 6.16), 4.89 (3.04, 7.89), 6.06 (3.27, 11.21), 6.99 (4.37, 11.19) and 9.17 (4.16, 20.21), respectively. By contrast, urinary lead, barium, iron, zinc, nickel, manganese and rubidium were negatively associated with asthma, with odds ratios (95% CI) of 0.48 (0.29, 0.80), 0.44 (0.27, 0.71), 0.41 (0.26, 0.64), 0.40 (0.24, 0.66), 0.30 (0.22, 0.41), 0.23 (0.14, 0.39) and 0.07 (0.03, 0.15), respectively. When comparing urinary metals in different subgroups of cases with those in matched controls, the associations of above 13 metals with asthma prevalence were nearly the same.

Conclusions: Our results suggested that asthma prevalence in the Chinese adults was positively associated with urinary chromium, chromium, selenium, molybdenum, cadmium, and uranium, and negatively associated with urinary manganese, iron, nickel, zinc, rubidium, barium and lead. Additional research with larger populations in different regions is required to support our findings.

Fig 1. Adjusted odds ratio and 95% confidential interval for asthma by considering urinary concentrations of metals as continuous variables.

The models were adjusted for educational level, occupational dust exposure, family history of asthma, tobacco smoking, pet ownership, flower gardening, physical activity, and body mass index.

Fig 2. Associations between urinary metals and asthma based on the multiple-metal models.

Metals were selected among 19 asthma-related metals from single-metal models by backward elimination in the multivariate logistic regression model (alpha = 0.05) with adjustment for age, gender, tobacco smoking, educational level, occupational dust exposure, family history of asthma, pet ownership, flower gardening, physical activity and body mass index. Abbreviation: OR: odds ratio; CI: confidential interval.

Fig 3. Associations between 13 metals in urine and asthma prevalence in the newly diagnosed asthma and matched controls based on the multiple-metal model.

The model was adjusted for age, gender, tobacco smoking, educational level, occupational dust exposure, family history of asthma, pet ownership, flower gardening, physical activity and body mass index. Abbreviation: OR: odds ratio; CI: confidential interval.