Lead exposure linked to 412,000 premature deaths in US each year, study finds

Exposure to traces of lead in petrol, paint and old plumbing may be linked to hundreds of thousands of premature deaths each year, according to new research.

As many as 412,000 Americans die prematurely every year - mostly from cardiovascular disease - due to historic exposure to low levels of the toxic metal, a US study suggests.

The figure is 10 times more than previously thought and could put deaths from lead exposure on par with smoking.

Lead was added to petrol until the 1990s to boost engine compression, and was also widely used to improve the performance of household paint before being banned in the US in 1978 and the EU in 1992 after

But lead pipes, once extensively used in plumbing, can still be found in older properties, while industrial emissions and contamination from smelting sites and batteries mean that some level of exposure to the metal continues.

Contact with lead is linked to high blood pressure, hardening of the arteries and coronary heart disease, but low-level exposure was not previously thought to increase mortality.

Professor Bruce Lanphear, who led the study at Canada’s Simon Fraser University, said: “Our study estimates the impact of historical lead exposure on adults currently aged 44 years old or over in the USA, whose exposure to lead occurred in the years before the study began.

“Today, lead exposure is much lower because of regulations banning the use of lead in petrol, paints and other consumer products, so the number of deaths from lead exposure will be lower in younger generations. Still, lead represents a leading cause of disease and death, and it is important to continue our efforts to reduce environmental lead exposure.”

The scientists analysed data from the Third Health and Nutrition Examination Survey (NHANES-III), a major study monitoring the health of US citizens.

Around 14,300 participants were followed for almost 20 years. All were given a medical examination at the start of the study that included a blood test for lead, with readings ranging from less than 1mg per decilitre of blood to 56mg.

People with high levels of at least 6.7mg were twice as likely to die from ischaemic heart disease compared with people having low levels of lead in their blood.

The condition is caused by muscle in the heart being starved of blood due to narrowed or blocked arteries.

Overall cardiovascular death risk was raised by 70 per cent by higher levels of lead exposure, the study found.

Researchers estimated that 28.7 per cent of cases of annual premature heart disease death in the US could be attributed to lead – a total of 256,000 deaths per year.

The findings are reported in The Lancet’s public health journal.

The study said “the estimated number of deaths from all causes and cardiovascular disease that were attributable to concentrations of lead in blood were surprisingly large; indeed, they were comparable with the number of deaths from current tobacco smoke exposure”.

People are more likely to suffer health complications from smoking, but lead exposure is far more common. About a fifth of Americans smoke, while 90 per cent of those who took part in the study were exposed to lead.

Prof Lanphear said: “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 USA, particularly from cardiovascular disease.

“Estimating the contribution of low-level lead exposure is essential to understanding trends in cardiovascular disease mortality and developing comprehensive strategies to prevent cardiovascular disease.

“Currently, low levels of lead exposure are an important, but largely ignored risk factor for deaths from cardiovascular disease. Public health measures, such as [upgrading] 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.”

Professor Kevin McConway, Emeritus Professor of Applied Statistics at the Open University, said: “The researchers make a very important point in their report – that it is more accurate to view this study as estimating how many deaths might have been prevented if historical exposures to lead had not occurred.

“In other words, they aren’t saying that current exposure to lead in the environment is the main thing here, as much of the exposure would have been in the past when regulation was much less strict than it is now. The lead author does state, however, that action needs to continue to reduce exposure.

“Lead tends to stay around in the body once it has entered it, so the blood lead levels of the people in this study will have been affected by exposure to lead throughout their lives: including exposure to lead in petrol before it was banned, and exposure from lead-based paint or lead drinking water pipes when those were more common than they are now.”

The study’s authors noted that outside factors could lead to “overestimation of the effect of concentrations of lead in blood, particularly from socioeconomic and occupational factors”.

In particular, they warned they were unable to adjust their findings to account for exposure to air pollutants or arsenic, both of which are risk factors for cardiovascular disease mortality.

Additionally, the study took only one reading of lead in participants’ blood, when levels were likely to have changed over time.

Tim Chico, Professor of Cardiovascular Medicine at the University of Sheffield, said the research did not prove that lead causes cardiovascular disease but “shows a strong association between levels of lead in the blood and future risk of heart attack and dying”.

He added: “This study suggests that lead, or factors that increase people’s exposure to lead, causes thousands more deaths every year than we previously recognised.”