PURPOSE: The purpose was to examine bronchial asthma according to cumulative exposure to fume particulates conferred by stainless steel and mild steel welding through a proxy of redeemed prescribed asthma pharmaceuticals.

METHODS: A Danish national company-based historical cohort of 5,303 male ever-welders was followed from 1995 to 2011 in the Danish Medicinal Product Registry to identify the first-time redemption of asthma pharmaceuticals including beta-2-adrenoreceptor agonists, adrenergic drugs for obstructive airway diseases and inhalable glucocorticoids. Lifetime exposure to welding fume particulates was estimated by combining questionnaire data on welding work with a welding exposure matrix. The estimated exposure accounted for calendar time, welding intermittence, type of steel, welding methods, local exhaustion and welding in confined spaces. Hazard ratios (HRs) with 95 % confidence intervals (CIs) were calculated using a Cox proportional hazards model adjusting for potential confounders and taking modifying effects of smoking into account.

RESULTS: The average incidence of redemption of asthma pharmaceuticals in the cohort was 16 per 1,000 person year (95 % CI 10-23 per 1,000 person year). A moderate nonsignificant increased rate of redemption of asthma medicine was observed among high-level exposed stainless steel welders in comparison with low-level exposed welders (HR 1.54, 95 % CI 0.76-3.13). This risk increase was driven by an increase risk among non-smoking stainless steel welders (HR 1.46, 95 % CI 1.06-2.02). Mild steel welding was not associated with increased risk of use asthma pharmaceuticals.

CONCLUSION: The present study indicates that long-term exposure to stainless steel welding is related to increased risk of asthma in non-smokers.