Low-level lead exposure leads to heart disease – Expert reaction

Almost one-third of early deaths from heart disease in the US could be because of cumulative low-level lead exposure, according to an international paper published in The Lancet Public Health

Researchers monitored the lead levels in more than 14,000 Americans over 20 years and found that even low-level lead exposure (between 1-5 micrograms of lead per decilitre of blood) increases the risk of premature death. The researchers say the study calls into question the assumption that there are ‘safe levels’ of lead exposure and suggests that low-level environmental lead exposure is a leading risk factor for premature death in the USA, particularly from cardiovascular disease.

The SMC asked public health experts to comment on the paper.

Professor Nick Wilson, Public Health Physician, University of Otago, comments:

“This new study is a large and well-conducted one. Furthermore, the findings are very plausible given that it is well established scientifically that lead exposure is linked to high blood pressure and heart disease. People in New Zealand also used to have relatively high lead levels – and so it is likely that many New Zealanders have also suffered from heart disease where exposure to lead (especially from lead in petrol) made some contribution.

“Indeed, this burden was prolonged due to the failure of many New Zealand Governments in the 1970s and 1980s to not act decisively despite good scientific evidence showing that lead levels were lowering the IQ of New Zealand children. But even if lead played some role in contributing heart disease it is unlikely to have been as important over the last 50 years in New Zealand as has smoking, a diet high in saturated fats from meat and dairy products, and physical inactivity.

“Fortunately, heart disease rates are currently declining as New Zealanders quit smoking, consume more healthy fats (like olive oil), and also take treatments such as blood pressure lowering drugs and statins.”

Terrie Moffitt, Nannerl O. Keohane University Professor, Duke University, USA; Associate Director, Dunedin Multidisciplinary Health and Development Study, University of Otago, comments:

“This important study alerts us to the possibility that people exposed to lead in years past can end up with heart disease years later.

“Environmental laws drastically reduced the amount of lead in New Zealand’s environment. But the older generation who are now entering the peak age of risk for heart disease are unaware their health may be still be affected today by lead they were exposed to as children, before the laws changed.

“It can be difficult for American studies like this one to isolate lead as an active ingredient in disease because Americans with the highest levels of lead in their blood tend to be poorer, less educated, heavy smokers, and eat an unhealthy diet. These factors all increase heart disease.

“In New Zealand, children of all backgrounds, rich or poor, breathed airborne lead before it was banned from petrol. If New Zealand studies also find a link between childhood lead and midlife heart disease, that would strengthen the evidence. The Dunedin Study plans to look into it.”

Note: As part of the Dunedin study, Terrie Moffit researched childhood exposure to high levels of lead in New Zealand cities in the 1970s and 1980s, which was found to be linked to lower IQ and socio-economic status in adulthood.

The Australian and UK Science Media Centres also gathered expert comments on the study.

Prof Kevin McConway, Emeritus Professor of Applied Statistics at The Open University, comments

“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.

“People starting their lives in the UK or USA now will, very likely, have lower blood lead levels when they grow up than did the people in this study, because several sources of lead pollution have been reduced. Assuming that the researchers’ statistical models are valid, numbers of cardiovascular deaths will decrease in the future because of those reductions in blood lead levels across the population.

“But, if lead has as strong a relationship to cardiovascular disease as these researchers describe, then changes in the level of lead in people’s blood in the past would have had major effects on numbers of deaths from cardiovascular diseases, particularly heart attacks.

“How much of the rise in deaths from heart disease over the past century might have been due to lead pollution, rather than all the other causes that have been put forward? Heart disease has been reducing in the UK and similar countries in recent decades; might this have more to do with reductions in lead levels than has been thought? I don’t think those questions can be answered in detail from this study alone, though the study may well lead to change in the way we understand trends in cardiovascular disease. Indeed, as the linked editorial by Landrigan points out, there may well be similar issues about several other pollutants.”

Prof Tim Chico, Professor of Cardiovascular Medicine and Honorary Consultant Cardiologist at the University of Sheffield, comments

“This paper shows a strong association between levels of lead in the blood and future risk of heart attack and dying. The relationship between lead levels and heart attack in this study was very strong; lead was potentially the cause of 37% of all deaths from heart attack in this study, which is about 10 times more than previous estimates.

“This is an “association study”; it can find a possible link between a factor like lead, and a disease such as heart attack, but it cannot prove that lead causes the disease directly. However, lead has a range of toxic effects on brain development and heart function and no known health benefits. The question is not therefore whether environmental pollutants such as lead cause premature death, but how many deaths, and this study suggests that lead, or factors that increase people’s exposure to lead, causes thousands more deaths every year than we previously recognised.

“In the last decades, we have made huge advances in understanding how to reduce an individual’s risk of heart disease; stopping smoking, regular physical activity, blood pressure and cholesterol lowering have all helped reduce the numbers of patients suffering a heart attack. It is likely that future advances will be less individual and more societal, such as redesigning transport systems and workplaces to encourage physical activity and global efforts to reduce exposure to pollutants such as lead and traffic fumes.”

Dr Ian Musgrave, Senior Lecturer, Pharmacology,  University of Adelaide, comments:

“Lead is a well known persistent environmental toxin. While most Australians would be aware of chronic exposure to lead’s effects on brain development and behaviour in children, fewer will be aware that long-term exposure to relatively low levels of lead increases blood pressure and the risk of heart and blood vessel disease.”

“The study looked at a representative sample of the adult US population. After measurement of blood lead and other baseline health measures, the subjects were followed for 17-22 years. Blood pressure and other health information, as well as causes of death, were followed over this time.

“The study’s strength is that it was able to follow a defined population over a sufficiently long time. However, the study only measured blood lead once, at the beginning of the study, and although they tried to correct for other causes of heart disease such as smoking and obesity, they may not have been able to correct all for possible contributory causes of death and so may overestimate the risk due to lead.

“In this study subjects with the highest levels of blood lead had a 37 per cent greater risk of premature death from any cause and a 70 per cent greater risk of death from heart disease.

“The study suggested that almost one-third of deaths due to heart disease was attributable to lead exposure. This estimate is about ten times higher than previous estimates, but the careful measurement of blood lead and the long-term followup make this estimate plausible.

“The other main finding is that lead levels generally considered to have minimal health impact were associated with higher death from heart disease. This suggests that lead has a larger public health impact than previously recognised. Even if the risks found in this study are an overestimate.

“While lead petrol was phased out in the 1970s, as was lead paint, recent studies show that some urban areas in Sydney and Melbourne have high soil lead levels, exceeding the Australian regulatory guideline of 300 mg/kg. This could potentially lead to exposures that will have adverse effects on heart health.”

Professor Stuart Khan, Civil & Environmental Engineer, University of New South Wales, comments:

“In decades past, drinking water was seen to be a comparatively minor source of exposure to lead for most people in Australia. That’s because there were other much more significant sources including leaded petrol and paints.

“However, since lead has been largely phased out for those uses, exposure through drinking water may be much more significant than it was.

“The city of Flint, Michigan in the USA has been dealing with a major water quality crisis regarding lead contamination since 2014.

“Although lead can enter drinking water from contaminated supplies, a more common problem involves lead being leached from pipes and other plumbing materials. This is particularly common where poor procedures have been used for welding and soldering. Household tap fittings, such as some water filters, can also contain lead-based components, which can leach lead into the water.

“Australian cities have a very wide variety of materials, which have been used for drinking water supply pipes and plumbing. As a result, we can expect that low levels of lead will continue to be detected in some Australian drinking water samples from time to time.

“Lead contamination in school plumbing systems is also something I believe we should be paying closer attention to. I think this is of particular concern when the students come back to school after a long summer break. Under those circumstances, there is potential for water to have sat stagnating, with warm summer temperatures, in the school plumbing system. These are ideal conditions for lead to be leached from the pipes to the drinking water.”