On the World Health Organization's list of 10 chemicals of major public health concern, lead is a familiar villain. The toxic metal contaminates air, soil, water and food, and builds up inside bodies over time. Its most widely publicized health impact is neurological damage in children, often measured in the loss of intelligence quotient (IQ) points. But lead's pernicious effects don't stop in childhood nor at the brain.
According to a new study in the journal Lancet Planetary Health, an estimated 5.455 million adults worldwide died in 2019 from cardiovascular disease (CVD) attributable to lead exposure — a toll more than six times higher than a previous estimate. The study goes on to provide what its authors say are the first monetary estimates of the total global cost of these lead-attributable deaths, along with the magnitude and cost of IQ loss in children under 5 years old.
For 2019 alone, the study puts the combined toll of cognitive damage and CVD mortality at $6 trillion (based on projected loss of future income and an economic measure known as value of statistical life), with the greatest burden falling on low- and middle-income countries.
Often associated with gasoline and paint, lead exposure can also be traced to lesser-known sources, such as cookware, water supply lines and electronic waste. "Many people believe that with the phase-out of leaded gasoline, the problem was solved," says co-author Ernesto Sánchez-Triana, the global lead for pollution management and circular economy at the World Bank (which funded the study, along with the Korea Green Growth Trust Fund). "What we have shown is that no, the problem is far away from solved."
Lead's link to cardiovascular health
Environmental lead exposure is known to cause cardiovascular disease, though some of the routes by which it does so are better understood than others. The new study uses a different method — the authors say a more comprehensive one — of counting lead-induced deaths from CVD than previous studies did.
For example, the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD), conducted by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, finds high blood pressure due to lead exposure caused an estimated 850,000 deaths in 2019. The contribution of lead exposure to hypertension is a well-established one, say IHME researchers.
Sánchez-Triana and his co-author, economist Bjorn Larsen, think that's a massive undercount of lives lost to lead — because, they contend, hypertension accounts only for a small portion of lead's deadly effects on the cardiovascular system. Lead exposure has also been linked with CVD through other effects, such as hardening of the arteries. Counting lead-induced deaths from those other effects, based on a 2020 health impact model drawing on U.S. data, Sánchez-Triana and Larsen extrapolated a dramatically higher global estimate at nearly 5.5 million people.
Michael Brauer, an environmental health researcher affiliated with IHME and the University of British Columbia, led the team that studied lead exposure for GBD 2019.
Brauer says his team at IHME continues to drill down into what portion of the world's nearly 20 million CVD deaths each year are attributable to lead exposure. Preliminary numbers for the forthcoming GBD 2021 study put that figure at 1.57 million, nearly double its 2019 estimate. Brauer says he questions the numbers at which Larsen and Sánchez-Triana arrived, but he agrees with them on a key point: Mortality from lead exposure deserves attention.
"Most people, when they think about lead, they actually think about effects on children and IQ," Brauer says. "In our estimates for a long time, the overall adult impact has been much larger than the impacts on childhood. So, I think this report is very helpful in the sense that I hope it will put a spotlight on the impact on adults."
The significance of a few IQ points
About those childhood impacts: Looking at the same year of 2019, Larsen and Sánchez-Triana estimated that children younger than 5 years lost a collective 765 million IQ points due to lead exposure. This, too, is a higher total than previous estimates, in part because it encompasses any amount of IQ loss due to lead in all kids worldwide. (GBD 2019 includes only major loss that dips below a certain threshold of intellectual disability, while another study from 10 years ago focused only on low- and middle-income countries.)
Larsen and Sánchez-Triana's findings indicate that the cognitive damage from lead exposure is greatest among kids in under-resourced countries where blood lead levels are highest: 95.3% of the lost IQ points were in low-income and middle-income countries, particularly in south Asia and sub-Saharan Africa. They estimated an average loss of 5.9 IQ points per child in low- and middle-income countries during the first five years of life, causing an average lifetime income loss per child of nearly 12%. Sánchez-Triana calls those numbers "shocking" and "absolutely terrifying."
"It's now understood quite clearly that any amount of lead in the blood of a child is going to be associated with some degree of IQ loss," says epidemiologist and pediatrician Philip Landrigan. Landrigan, who was not involved in Larsen and Sánchez-Triana's study, directs the Global Public Health Program and Global Observatory on Planetary Health at Boston College; his early research on the effects of low-level lead exposures on children contributed to the U.S. government's decision to ban leaded paint and gasoline in the 1970s.
According to Landrigan, while small drops in IQ might not show up during a standard pediatric exam the way severe impairment would, they matter: "With a five- or a six-point loss in IQ, a child is going to do less well in school, perform less well on standardized exams, be at greater risk of dyslexia, be at increased risk of school dropout and be at increased risk for drug abuse and incarceration during their adolescent and early adult years."
In Landrigan's view, the new study fills a significant gap in our knowledge about lead by quantifying the overall impact of these established cognitive effects. "This makes use of the best data available and looks at the problem globally, in its totality," he says. "I think it's a very important piece."
The heaviest burden on the poorest countries
Even with leaded gasoline out of play, many sources of lead poisoning remain. For example, fewer than half of the world's countries have introduced legally binding controls on lead paint.
When Pure Earth, an organization devoted to reducing environmental toxins, recently tested hundreds of samples of ceramic and metallic foodware in 25 low- and middle-income countries, it found roughly half of those samples had concentrations of lead exceeding regulatory standards set by the United Nations, European Union and the United States. Pure Earth's report, published in September, also found concerning levels of lead in cosmetics, toys, spices and other foods and household goods.
Larsen and Sánchez-Triana advocate for the systematic identification of such sources, periodic national blood lead level measurements in low- and middle-income countries — and appropriate legislative responses to reduce lead pollution and exposure.
Sánchez-Triana applauds one such solution: the 2021 announcement that the U.S. will invest billions of dollars to replace lead pipes nationwide. "That's something that should be replicated globally," he believes.
"Legislation is the fundamental tool in most countries for reducing exposures to toxic substances," says Landrigan, who notes that lead levels in the U.S. dropped by more than 95% in the decades following the EPA crackdown on leaded gas and paint. Does he think studies like this one can help create momentum for global action?
"It's not the whole story, but it's an essential first step," he says.
Nicole Estvanik Taylor is a freelance writer based in the Boston area. Her past roles include managing editor of American Theatre magazine and content director of the MIT Alumni Association.
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