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Does cadmium contribute to the development of smoking induced emphysema?
Most respiratory physicians recognise that chronic exposure to respirable cadmium in the workplace may lead to emphysema. What may come as a surprise is that cadmium is a constituent of tobacco and hence cigarette smoke, and so is inhaled outside the workplace by all smokers. The question arises whether inhaled cadmium may contribute to, or even be the principal cause of, smoking induced emphysema.
Mannino and colleagues have taken advantage of the Third US National Health and Nutritional Examination Survey (NHANES III) to investigate the matter, since it allowed them to compare creatinine adjusted urinary cadmium levels with spirometric measurements in as many as 16 024 subjects, representative of the adult US population. Their findings are presented in this issue of Thorax.1 Not only was there an increasing trend in urinary cadmium levels from never, through former, to current smokers, but among the current and former smokers (though not the never smokers) urinary cadmium was correlated negatively with forced expiratory volume in 1 second (FEV1) and the ratio of FEV1 to forced vital capacity (FVC) after adjustments for potential confounders. They concluded that cadmium might indeed contribute importantly to tobacco related lung disease.
Is this plausible? If so, is it likely? Neither question can be answered easily, and there is a possible alternative explanation for the observed association. Urinary cadmium may simply be a marker of cumulative exposure to tobacco smoke.
CADMIUM SOURCES, UPTAKE, AND METABOLISM
Cadmium occurs within zinc, copper, and lead ores and its concentration in soil varies widely (typically 0.01–7.0 ppm). This influences the amount in local drinking water and the amount delivered into tobacco leaves and other plants. In the absence of occupational exposure, cadmium enters the body in trace amounts within drinking water and foodstuffs, and …
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