After an average of 19.3 years, 4422 people died including 1801 from cardiovascular disease and 988 from heart disease. "And instead of it being 40,000 deaths, which is what had previously been estimated, we found that it was about 10 times that", Lanphear said.
"It also suggests that even "low-level" exposure increases health risks".
"Nobody had even tried to estimate the number of deaths caused by lead exposure using a nationally representative sample of adults", Dr Bruce Lanphear, a professor of health sciences at Simon Fraser University and a leading author of the study told CNN.
"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", Lanphear said. Lanphear and his team sought to determine how exposure to lead contributes to all-cause mortality and cardiovascular disease (CVD) mortality in the U.S.
The study used data from the Third National Health and Nutrition Examination Survey (NHANES-III) for 14289 people in the United States of America aged 20 years or older between 1988 and 1994, and the end of 2011.
Around 14,300 participants were followed for nearly 20 years.
Metin Avkiran, associate medical director at the British Heart Foundation, said: "This study adds to the substantial evidence that exposure to lead can have long-term consequences".
People with high blood levels had a 70 percent greater risk of dying from cardiovascular disease than those with lower levels.
Previous estimates, which assumed that low-level lead exposure did not increase the risk of premature death, produced substantially fewer deaths.
So, what is the link between lead exposure and heart disease?
More than 400,000 deaths annually from ischemic heart disease and CVD may be attributable to low levels of lead exposure, according to findings recently published in Lancet Public Health.
For example, people with the highest lead levels were more likely to be men, smokers, and less educated, with poorer diets, high cholesterol, hypertension and diabetes, all of which are risk factors for cardiovascular disease. About a fifth of Americans smoke, while 90 per cent of those who took part in the study were exposed to lead.
"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 U.S., particularly from cardiovascular disease", Professor Lanphear said.
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".
Baseline blood lead levels ranged from less than 1 μg/dL to 56 μg/dL. After looking at how many people died during this period-about 4,400 in total, 1,800 of those from cardiovascular disease-the study in the Lancet Public Health journal found about 256,000 deaths each year could be tied to lead exposure.