Modeling studies show that lead poisoning has a far greater impact on global health than previously thought, potentially killing more than 5 million people each year and posing a similar threat to air pollution. The study, dubbed a "wake-up call," also estimates that exposure to toxic metals costs young children in developing countries an average of nearly six IQ points each. Lead contamination has been shown to cause a range of serious health problems, particularly related to heart disease and brain development in young children, so leaded gasoline has been banned worldwide.
IQ loss function for blood lead levels from Crump and colleagues. Blood lead levels refer to the lifetime average blood lead levels in children under 5 years old. According to Crump and colleagues, the solid line is the central estimate and the shaded area is the 95% CI. IQ=Intelligence Quotient. Source: The Lancet Planetary Health (2023). DOI:10.1016/S2542-5196(23)00166-3
But people can still be exposed to this potent neurotoxin through food, soil, cooking utensils, fertilizers, cosmetics, lead-acid car batteries and other sources.
Two World Bank economists who authored the study, published in the journal Lancet Planetary Health, said it was the first to assess the impact of lead exposure on heart disease deaths and IQ decline in children in rich and developing countries.
Lead author Bjorn Larsen told AFP that when they first saw the number calculated by their model, they were shocked because it was so "huge".
Their model estimates that 5.5 million adults died from heart disease due to lead exposure in 2019, 90% of whom were in low- and middle-income countries. This is six times higher than previous estimates and accounts for approximately 30% of deaths from cardiovascular disease, the leading cause of death globally.
That means lead exposure is more likely to cause heart disease than smoking or cholesterol, Larson said.
The study also estimates that children under the age of five globally lost a cumulative 765 million IQ points due to lead poisoning in 2019, 95% of which were from developing countries. This figure is nearly 80% higher than previous estimates.
World Bank researchers believe that the economic losses caused by lead exposure in 2019 were as high as $6 trillion, equivalent to 7% of global gross domestic product.
In their analysis, the researchers used estimates of blood lead levels in 183 countries from the landmark 2019 Global Burden of Disease Study.
Previous studies have only measured lead's impact on heart disease when it raises blood pressure. But the new study came up with a higher number by looking at the many other ways lead affects the heart, such as hardening of the arteries that can lead to stroke, Larson said.
Roy Harrison, an air pollution and health expert at the University of Birmingham in the United Kingdom who was not involved in the study, told AFP that the study was "interesting but there are a lot of uncertainties." For example, the relationship between lead in the blood and heart disease was based on a U.S. survey. The model uses estimates of lead levels in blood in many developing countries, rather than test values. But if these results are confirmed, "they would have significant public health implications, but for now, it's just an interesting hypothesis."
Richard Fuller, president of the NGO Pure Earth, said surveys in developing countries did test lead levels in blood, but they mostly found levels higher than the new study estimated.
He told AFP this meant "the effects of lead may be more severe than reported", calling it a "wake-up call".
"We're still in the dark" when it comes to understanding the extent to which different sources of lead contribute to blood contamination, Larson said. The "missing pieces of the puzzle" are revealed in a Pure Planet report released on Tuesday, which analyzed 5,000 consumer products and food samples from 25 developing countries. The report found high rates of lead contamination in metal pots, ceramic cookware, paint, cosmetics and toys.
This is why lead poisoning is so high in poor countries. "It was the items in the kitchen that poisoned them."