New research has found that the deaths of an estimated 250,000 Americans from cardiovascular disease each year may be linked to lead exposure — a number far higher than previous estimates.
The study was based on a national health survey that tracked more than 14,000 participants across the country over nearly two decades.
Medical researchers have long known that lead poisoning damages children’s brains and increases the risks of all sorts of health problems from high blood pressure to heart disease.
In previous studies, they had assumed that low levels of lead in people’s blood wouldn’t increase the risk of death. But even minute levels of lead substantially increase the risk of death, especially from heart disease, the new study found.
“We saw risk down to the lowest measurable levels,” said Bruce Lanphear, a lead-poisoning researcher at Simon Fraser University in British Columbia who led the study. “It’s a big deal, and it’s largely been ignored when it comes to cardiovascular disease deaths.”
Lead levels in the air have declined dramatically in the United States since the country began phasing out leaded gasoline in the 1970s. But lead water pipes are still being used in communities scattered across the country, and lead paint remains in many old houses.
Workers at construction sites and auto shops may be exposed to lead. It’s released into the air by coal-fired power plants, lead smelters and other industrial facilities, including recyclers that work with lead batteries. Lead comes in products like fishing weights, lead-glazed ceramics and some children’s toys. It turns up in some foods, such as baby foods.
The new study, published Monday in The Lancet Public Health journal, is the first to estimate the number of deaths linked to low-level lead exposure in the U.S. using data from a nationally representative sample.
Cardiovascular disease is the top cause of death for Americans, and the study indicates lead is a major factor contributing to those deaths.
How the study worked
The research focused on 14,289 people followed in the national health survey between 1988 and 1994, and again in 2011. Their health data included a blood test for lead.
By the end of the period, 4,422 people had died, including 1,801 from cardiovascular disease, out of which 988 deaths were from coronary heart disease.
The researchers adjusted the results for a list of factors such as age, sex, alcohol consumption, smoking and diet, and estimated the proportion of deaths in U.S. adults ages 44 or older whose premature deaths could have been prevented if they hadn’t been exposed to lead.
They estimated that 256,000 deaths — nearly 29% of premature deaths from cardiovascular disease — could be linked to lead exposure each year. That included 185,000 deaths from coronary heart disease, or about 37% of all deaths from that cause, as well as other types of cardiovascular disease, such as strokes and peripheral artery disease.
Previous studies assumed no harm occurred when patients had lead in their blood at concentrations of less than 50 parts per billion. About four out of five people surveyed had lead concentrations below that level, yet their cases still showed increasing risks with incremental rises in lead levels.
The results point to a need for the federal Environmental Protection Agency, as well as other federal and state agencies, to ratchet down the allowable levels of lead under their standards, Lanphear said.
Lead standards 'too high to protect kids'
“The levels of lead in standards right now are too high to protect kids,” Lanphear said. “And this new study would suggest that they’re too high — whether it’s lead in water, lead in house dust, lead in air — all of those things should be re-evaluated based upon this study because it suggests that there’s no safe level of lead.”
Lanphear and his colleagues also looked at deaths from all causes and estimated that about 400,000 deaths per year are attributable to lead exposure in the United States.
That’s 10 times larger than the current estimate and about 18% of all deaths. It’s also comparable to the approximately 480,000 current smokers who die in a given year.
Those numbers are based on the amounts of lead that older Americans were exposed to decades ago. Most Americans are exposed to less lead today because of its removal from gasoline and paint, Lanphear noted.
“So the number of deaths from lead exposure will be lower in younger generations,” he said. “Still, lead represents a leading cause of disease and death, and it is important to continue our efforts to reduce environmental lead exposure.”
Low lead levels in children's blood have been linked to lower IQs, slowed growth and behavioral and learning problems.
The crisis of lead-contaminated drinking water in Flint, Mich., focused more attention on the long-neglected problem of lead pipes in water systems across the country. In 2016, an investigation by the USA TODAY Network found nearly 2,000 water systems in all 50 states where testing showed excessive levels of lead contamination during the previous four years.
Reducing the amounts of lead that people are exposed to will require a variety of measures, Lanphear said, including changing health standards, abating lead paint in older homes and phasing out leaded fuel still used for some planes.
“Single-piston jet engines for these little planes at regional airports continue to use leaded gasoline,” Lanphear said, “and you can see measurable increases in the children who live closest to those regional airports.”
Findings offer 'a new window on heart disease'
Philip Landrigan, dean for global health at the Icahn School of Medicine at Mount Sinai in New York, said the study "sort of opens up a new window on heart disease." Landrigan was not involved in the study.
Cardiologists and other doctors will probably start making blood-lead testing a standard part of their procedures in the next few years, Landrigan said, as lead becomes added to a list of long-recognized risks for heart disease including smoking, high blood pressure and obesity.
Beyond that, he said, the findings underscore the importance of doing away with remaining lead pipes and lead paint across the country.
“I think we have to really mobilize the resources in this country to get rid of that lead. We know how to do it, but we haven’t had the political leadership or the willingness to spend the money,” Landrigan said.
“Anything that we could do that could knock heart disease down by 10 or 15% is saving a lot of lives.”
In a commentary article that accompanied the study, Landrigan wrote that deaths from cardiovascular disease increased 12.5% worldwide from 2005 to 2015 and that the biggest increases occurred in rapidly developing “low-income and middle-income countries,” which are industrializing and coping with pollution.
Until now, he said, little attention has focused on the possible contribution of lead, or the contribution of all types of pollution.
Countries worldwide have phased out leaded gasoline. But lead production still grows, driven partly by global demand for car batteries.
While the study focused only on the United States, Lanphear said the findings have important implications for places where high levels of lead are much more prevalent, such as India and countries in Southeast Asia.
Next up for the research: Questions and skepticism
Howard Hu, a professor of environmental public health at the University of Toronto who wasn’t involved in the study, said the findings were impressive and in line with previous studies.
“I’m sure there’ll be a lot of critical interpretation and skepticism,” Hu said.
He said he expects critics may question whether it’s really the level of lead that’s driving the trends, or “is it a proxy for some other unmeasured thing?”
“People will be scratching their heads trying hard to think of what else it could be a proxy for. I think they can think hard, but it’s hard to explain it away,” said Hu, who has studied how lead affects chronic diseases.
“It would be really hard to explain this away as really just an effect representing something else.”
Lanphear’s team included researchers from the University of California-Berkeley, the University of Rochester School of Medicine and Dentistry and the University of Cincinnati School of Medicine.
They used standard, accepted methods to account for other factors like tobacco use, Hu said: “There are some things that one could argue could be measured better, like socioeconomic status, and they acknowledged that there might still be some undetected influence of socioeconomic status.”
Among other limitations, the study’s authors said they were unable to control for factors such as people’s exposure to arsenic or air pollution, which also pose health risks.
There are still pockets of people exposed to high levels in the U.S., Hu noted, despite improvements.
“And it unfortunately now tracks even more towards poverty — living in old housing where there’s lead paint or lead plumbing or living close to factories that are still emitting lead.” Hu said.
“We’ve done a pretty good job of reducing exposures over time, but there’s still lots more to do, as illustrated by the Flint water crisis.”
While it’s troubling that lead has long been overlooked as a major risk factor, Lanphear said, there’s also a hopeful side to the research.
“To the extent that we can identify risk factors, like lead or air pollution, and we can actually modify them, it’s really hopeful because it means that we know what to do to dramatically reduce deaths from heart disease,” he said.
And if the country takes the issue seriously in the coming years, he said, far fewer people could end up dying from heart disease.
Follow Ian James on Twitter: @TDSIanJames