Lead poisoning has a far greater impact on global health than previously thought, potentially contributing to over five million deaths a year and posing a similar threat to air pollution, research suggested.

The study, described as "a wake-up call", also estimated that exposure to the toxic metal causes young children in developing countries to lose an average of nearly six IQ points each.

Lead pollution has been shown to cause a range of serious health problems, particularly relating to heart disease and the brain development of small children, resulting in leaded gasoline being banned worldwide.

But people can still be exposed to the potent neurotoxin via food, soil, cookware, fertilisers, cosmetics, lead–acid car batteries and other sources.

The two World Bank economists who authored the study, published in the Lancet Planetary Health journal, said it was the first to assess the impact of lead exposure on heart disease deaths and child IQ loss in wealthy and developing nations.

Lead author Bjorn Larsen told AFP that when the pair first saw the figure their model calculated, "we didn't even dare to whisper the number" because it was so "enormous".?

Their model estimates that 5.5 million adults died from heart disease in 2019 because of lead exposure, 90 percent of them in low- and middle-income countries.

It would mean that lead exposure is a bigger cause of heart disease than smoking or cholesterol, Larsen said.

$6 trillion cost

The research also estimated that children under five lost a cumulative 765 million IQ points due to lead poisoning globally in 2019, with 95 percent of those losses coming in developing countries. That number is nearly 80 percent higher than previously estimated. ?The World Bank researchers put the economic cost of lead exposure at $6 trillion in 2019, equivalent to seven percent of global gross domestic product. For the analysis, the researchers used estimates of blood lead levels in 183 countries taken from the landmark 2019 Global Burden of Disease study. Previous research had measured only lead's effect on heart disease when it came to raising blood pressure. But the new study looked at numerous other ways lead affects hearts, such as the hardening of arteries that can lead to stroke, resulting in the higher numbers, Larsen said.?

That is six times higher than the previous estimate, and represents around 30 percent of all deaths from cardiovascular disease – the leading cause of death worldwide.

For example, the relationship between lead in blood and heart disease is based on a survey in the United States, and whether those findings could be applied worldwide "is a huge jump of faith", he said.

Researchers also pointed out that the model used estimations – not tests – of lead in blood in many developing countries.

If the results were confirmed-they would be of major public health significance, but at present, this is simply an interesting hypothesis.