Partial Mediation by Cadmium Exposure of the Association Between Tobacco Smoking and Atherosclerotic Plaques in the Carotid Artery.

Exposure to cadmium confers increased cardiovascular risk. Tobacco smoke contains cadmium, which, hypothetically, may mediate parts of the tobacco-associated risk of developing atherosclerotic plaques. Baseline data from the Swedish Malmö Diet and Cancer cohort (1991-1996) were used to test this hypothesis. Mediation analysis was used to examine associations between smoking and blood cadmium levels and the prevalence of ultrasound-assessed carotid atherosclerotic plaques. The total association with smoking status (never smokers, 2 categories of former smokers, and current smokers) was split into direct and indirect association, and the proportion mediated was estimated. The adjusted estimated plaque prevalence was approximately 27% among never smokers. We identified both a direct and an indirect pathway between smoking and carotid plaques; the indirect association, through cadmium, was observed among current smokers and former smokers who had quit smoking less than 15 years before. For current smokers, the prevalence ratio for plaque was 1.5, with 60%-65% of the association with smoking being mediated through cadmium. Recent former smokers had a prevalence ratio of 1.3, and 40%-45% was mediated through cadmium. Long-time former smokers had a prevalence ratio of 1.2, but none of the association was mediated through cadmium. In conclusion, about two-thirds of the proatherosclerotic association with smoking was mediated by cadmium.