Using these risk levels, the researchers estimated 412,000 deaths each year in the USA could be attributed to lead exposure, including 256,000 from cardiovascular disease. Lead was once widely used in petrol, plumbing, paint, and other consumer products, but as it emerged that high exposure to the chemical - defined as having a blood lead level of 5 micrograms per deciliter (μg/dL) or higher - can be toxic to humans and animals, efforts have been made to reduce its use.
"Public health measures such as abating older housing, phasing out lead-containing jet fuels, replacing lead-plumbing lines and reducing emissions from smelters and lead battery facilities will be vital to prevent exposure".
"What this study suggests is there's no apparent safe level" for adults, said the principal author of the study, Bruce Lanphear of Simon Fraser University, in Canada.
Researchers analyzed blood and urine tests from 14,289 patients older than 20 years (mean geometric concentration of lead in blood, 2.71 µg/dL).
He said: "The estimated number of deaths from all causes and cardiovascular disease that were attributable to concentrations of lead in blood were surprisingly large; indeed, they were comparable with the number of deaths from current tobacco smoke exposure".
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Metin Avkiran, associate medical director at the British Heart Foundation, said: "This study adds to the substantial evidence that exposure to lead can have long-term consequences".
Around 14,300 participants were followed for nearly 20 years. "The information that emerges from this reassessment will increase understanding of lead's contribution to mortality from non-communicable diseases, could foster collaboration between the environmental and chronic disease research communities, guide realignment of cardiovascular disease prevention strategies, and ultimately save lives".
The study revealed that adults who had high lead levels in their blood were 37 percent more likely to die from all causes during the follow-up period, compared with those who had a lower level of 1 μg/dL.
Tim Chico of the University of Sheffield told the paper: "This study suggests that lead, or factors that increase people's exposure to lead, causes thousands more deaths every year than we previously recognised".
Lead has always been marked out as a toxic substance and has been phased out since the 1990s to reduce its environmental impact.
"Our study findings suggest that low-level environmental lead exposure is an important risk factor for death in the United States of America, particularly from cardiovascular disease", Lanphear and colleagues wrote. The US Occupational Safety and Health Administration (OSHA) requires employers to remove workers from exposure when their blood lead levels rise to 50 µg/dL in the construction industry or 60 µg/dL in other industries, and they can return to work when their blood lead levels go down to 40 µg/dL. In addition, they were unable to control for all potential confounders such as air pollution or arsenic exposure, both of which are established CVD risk factors. The risk factor is even higher for people with cardiovascular disease, given that lead exposure is linked to high blood pressure, the hardening of the arteries and ischemic (coronary) heart disease.