Are 'Safe' Levels of Lead and Cadmium Still Dangerous?

Blood levels of two metals lead and cadmium may increase the risk of peripheral artery disease, even at levels currently considered safe, according to research published in the June 8 issue of Circulation: Journal of the American Heart Association.

The general public can be exposed to lead and cadmium through cigarette smoke, in ambient air near industrial and combustion sources, in certain foods and sometimes in drinking water. Peripheral artery disease (PAD) affects 8 to 12 million Americans, according to the American Heart Association. It is a condition similar to coronary artery disease and carotid artery disease.

In PAD, fatty deposits build up in artery walls and reduce blood circulation, mainly in arteries to the legs and feet. In its early stages a common symptom is cramping or fatigue in the legs and buttocks during activity. Such cramping subsides when the person stands still.

In a study of 2,125 adults, those with the highest blood concentrations of lead or cadmium were almost three times more likely to develop PAD than those with the lowest levels of the two metals. Yet the highest levels were well within what is currently considered safe levels, said senior author Eliseo Guallar, M.D., DrPH, an assistant professor of epidemiology at the Johns Hopkins University Bloomberg School of Public Health in Baltimore.

Both metals are well-known toxins, Guallar said, but the levels found in the subjects "are well below the radar screen of current regulations."

There was a significant association between cadmium blood levels and PAD. People with the highest cadmium levels were 2.82 times more likely to develop PAD than people with the lowest levels.

The trend in the association between PAD and blood lead from the lowest quartile to the highest quartile was significant. The odds ratio for developing PAD was 2.88 for those with the highest blood lead levels compared to those with the lowest levels of lead in their blood.

PAD was associated with blood lead concentrations that were 13.8 percent higher on average than in subjects without PAD, Guallar said. Likewise, the cadmium levels were about 16.1 percent higher in persons with PAD than in those without PAD.

Guallar said that as research has uncovered more information about the true dangers of lead, regulators steadily lowered the threshold for so-called "safe" levels. "A decade ago, what was considered a safe level for lead was much higher than it is today," he said.

PAD is strongly associated with smoking, which is confirmed in the present study, Guallar said. In this study the odds of PAD for current smokers compared to people who never smoked was 4.13. The odds were reduced to 3.38 after adjustment for blood lead and to 1.84 after adjustment for blood cadmium. This led Guallar to theorize that the cadmium contained in cigarette smoke may damage the lining of blood vessels and be a major factor in smoking-associated PAD.

"We don't need any more reasons to argue that smoking is bad, but it is important to know what are the mechanisms of the problems associated with smoking. We need to know if there is something about cigarette smoke that makes it more specific to PAD than other vascular diseases," he said.

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