Past exposure to lead may be to blame for over 400,000 deaths in the United States every year, according to a new study published in The Lancet Public Health.
From an analysis of more than 14,000 people in the U.S., researchers found that exposure to low lead levels from the late 1980s to the mid-1990s was linked to a higher risk of cardiovascular and all-cause death over the next 20 years.
Led by Prof. Bruce Lanphear, from Simon Fraser University in Canada, the study is the first to use a nationally representative sample to investigate how low levels of lead exposure affect mortality in the U.S.
Lead is a chemical element that is naturally present in soil and water. 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.
However, the new study from Prof. Lanphear and colleagues suggests that even lower levels of lead exposure can pose significant harm to health.
The health risks of lead exposure
According to the U.S. Environmental Protection Agency (EPA), children are most susceptible to the harms of lead exposure; their developing bodies absorb the chemical in higher amounts and their brains and nervous systems and more sensitive to it.
In children, lead exposure may cause developmental, behavioral, and learning problems, as well as anemia and problems with hearing.
In adults, exposure to lead may cause reproductive problems, a reduction in kidney function, and increased blood pressure.
For this latest research, Prof. Lanphear and his team sought to determine how exposure to lead contributes to all-cause mortality and cardiovascular disease (CVD) mortality in the U.S.
"No studies have estimated the number of deaths in the U.S.A. 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 U.S.A., are associated with cardiovascular mortality," the researchers explain.
To reach their findings, the team analyzed the data of 14,289 adults in the U.S. who were a part of the Third National Health and Nutrition Examination Survey.
Subjects were enrolled in the study between 1988 and 1994. Blood samples were taken from each participant at study baseline, and these were measured for levels of lead.
"Our study estimates the impact of historical lead exposure on adults currently aged 44 years old or over in the U.S.A., whose exposure to lead occurred in the years before the study began," explains Prof. Lanphear.
Even low levels of lead are harmful
Baseline blood lead levels ranged from less than 1 μg/dL to 56 μg/dL. The average blood lead level was 2.7 μg/dL, and a total of 3,632 study participants had a level of 5 μg/dL or higher.
Over an average 19.3 years of follow-up, a total of 4,422 deaths occurred. Of these, 1,801 were from CVD and 988 were from heart disease.
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.
These subjects were also 70 percent more likely to die from CVD, and their risk of death from heart disease was doubled.
Using these data, the team calculated that blood lead levels higher than 1 μg/dL are responsible for around 412,000 deaths in the U.S. each year. Of these, around 256,000 are from CVD.
These results remained after accounting for a number of possible confounding factors, including participants' age, sex, body mass index (BMI), diet, smoking status, and alcohol intake.
Are there any 'safe levels' of toxicants?
Prof. Lanphear and team admit that there are some limitations to their research. For example, they point out that their study relied on a single blood test from each subject at baseline, so they were unable to determine the "effect of further lead exposure."
Additionally, they note that they could not control for exposure to other contaminants that might affect cardiovascular health, such as arsenic or air pollution.
Still, these results indicate that lead exposure could have a larger impact on our health than we thought.
"Our study calls into question the assumption that specific toxicants, like lead, have 'safe levels,' and suggests that low-level environmental lead exposure is a leading risk factor for premature death in the U.S.A., particularly from cardiovascular disease."
Prof. Bruce Lanphear
"Currently, low levels of lead exposure are an important, but largely ignored risk factor for deaths from cardiovascular disease," adds Prof. Lanphear.
"Public health measures," he goes on, "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 lead exposure."