As many as 412,000 Americans die prematurely every year - mostly from cardiovascular disease - due to past exposure to small amonts of the toxic metal, a new USA study suggested. There's also ongoing exposure from foods, emissions from industrial sources and contamination from lead smelting sites and lead batteries, the researchers explained.
From the 1990s until 2015, the US Centers for Disease Control considered anything less than 10 µg/dL to be a "low" level of exposure for adults, though the CDC does not consider any level of lead to be "safe".
To reach their findings, the team analyzed the data of 14,289 adults in the US who were a part of the Third National Health and Nutrition Examination Survey. All participants had a medical exam and a blood test for lead at the start of the study.
However, they acknowledged the use of a single baseline lead value to predict outcomes over the following 20 years was not ideal; serial measurements may have been more informative.
"No studies have estimated the number of deaths in the United States of America attributable to lead exposure using a nationally representative cohort, and it is unclear whether concentrations of lead in blood lower than 5 μg/dL, which is the current action level for adults in the United States of America, are associated with cardiovascular mortality", the researchers explain.
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".
But efforts to reduce environmental lead exposure is still vital, he said.
"Low levels of lead exposure are an important, but largely ignored, risk factor for death from cardiovascular disease", mainly heart attacks and strokes, said lead author Bruce Lanphear, a professor at Simon Fraser University in Canada.
The link held even at low-level exposure to lead. "This study suggests that estimating the contribution of environmental lead exposure is essential to understand trends in cardiovascular disease mortality and develop comprehensive strategies to prevent cardiovascular disease", they concluded.
"Lead tends to stay around in the body once it has entered it, so the blood lead levels of the people in this study will have been affected by exposure to lead throughout their lives: including exposure to lead in petrol before it was banned, and exposure from lead-based paint or lead drinking water pipes when those were more common than they are now".
An increase in lead concentration from the 10 to the 90 percentile was linked to a 37 percent greater chance of all-cause mortality, a 70 percent greater chance of cardiovascular mortality and a 2.08-fold risk of death from ischemic heart disease. 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. A total of 4,422 people died during a median follow-up of 19.3 years: 38 percent from cardiovascular disease and 22 percent from ischemic heart disease.