Urinary heavy metals and chronic obstructive pulmonary disease (COPD): Results from National Health and Nutrition Examination survey (NHANES) 1999-2008

Chronic heavy metal exposure is thought to play a role in pathogenesis COPD. We aim to study the association between COPD and long-term heavy metal exposure assessed using urine heavy metal concentration.

Methods Cross-sectional data from NHANES 1999- 2008 were used. COPD was determined using standardized questionnaire including history of emphysema, or active or past chronic bronchitis. Survey statistics traditionally used to analyze complex semi-random survey designs were employed to analyze these data. Data were pooled using standard methods, and 10 year combined weights were calculated. Urinary heavy metal levels were measured by mass spectrometry. Fourteen heavy metals were studied: barium, beryllium, cobalt, cadmium, cesium, lead, platinum, thallium, tungsten, mercury, antimony, molybdenum, uranium and arsenic. We log transformed urinary metal concentrations (μg/mg of urinary creatinine) in logistic regression equations.

Results Our sample population (612 COPD and 7570 non-COPD participants) translated to a prevalence estimate of 7.5% (SE 0.4) amongst non-institutionalized US population. Statistically significant associations between COPD and two heavy metals were observed: cadmium [adjusted OR: 2.67 (95% CI: 1.83-3.90)] and cobalt [adjusted OR: 1.49 (95% CI: 1.01-2.20)]. When stratified by COPD category, urinary cobalt concentrations were associated with increased risk of chronic bronchitis and urinary cadmium concentrations were associated with increased risk of chronic bronchitis and emphysema.

Conclusions Significant association between urinary cadmium and cobalt with COPD was observed. Human exposure to heavy metals from several discrete sources (cigarette smoke, air pollution, food and water) in our environment may have important implications on pulmonary morbidity.