New estimates suggest that 256000 premature deaths from cardiovascular disease – including 185000 deaths from ischemic heart disease – in the USA may be linked to historical lead exposure in middle-aged and older adults (people currently aged 44 years or over), according to an observational study following 14300 people for almost 20 years, published in The Lancet Public Health journal.
Previous estimates, which assumed that low-level lead exposure did not increase the risk of premature death, produced substantially fewer deaths. However, this new study finds that low-level lead exposure (between 1-5 micrograms of lead per decilitre of blood) increases the risk of premature death, especially from cardiovascular disease. Lead exposure is linked to high blood pressure, hardening of the arteries and ischemic (coronary) heart disease.
Exposure occurs from lead that remains in the environment from historic use in fuel, paint and plumbing, as well as ongoing exposures from foods, emissions from industrial sources, and contamination from lead smelting sites and lead batteries.
This study is the first to estimate the number of deaths in the United States from low-level lead exposure using a nationally-representative sample.
The study used data from the Third National Health and Nutrition Examination Survey (NHANES-III) for 14289 people in the USA aged 20 years or older between 1988 and 1994, and the end of 2011. All participants had a medical examination, including a blood test for lead – a measure of past and ongoing exposures to lead – and a urine test for cadmium at the start of the study.
After an average of 19.3 years, 4422 people died including 1801 from cardiovascular disease and 988 from heart disease.
At the outset, the average level of lead found in the participants’ blood was 2.7 µg/dL, but ranged from less than 1 to 56 µg/dL. One in five participants (3632 people) had levels of 5 µg/dL or more, and those with the highest levels of lead in their blood were older, less educated, more likely to be male, smoke, consume larger amounts of alcohol, have less healthy diets, have higher cholesterol, and more likely to have hypertension or diabetes.
Almost one in 10 participants had lead levels that were undetectable to the blood test, so were given a reference level of 0.7 µg/dL (8%, 1150/14289 participants).
Overall, people who had high lead levels (6.7 µg/dL) were at 37% greater risk of premature death from any cause, 70% times greater risk of cardiovascular death, and double the risk of death from ischemic heart disease, compared with people with lower levels (1 µg/dL).
Using these risk levels, the authors also estimated the current proportion of deaths in adults aged 44 years or older in the USA that could have been prevented if historical exposure to lead had not occurred.
Overall, they found that up to 18% of all deaths every year in the USA (412000/2.3 million) would be among people who had levels of lead above 1 µg/dL. They estimated that 28.7% of premature cardiovascular disease deaths (256000/ 892000) could be attributable to lead exposure, including a high proportion of ischemic heart disease deaths (lead was linked to 37.4% of all IHD deaths [185000/495000]).
These results were adjusted for age, sex, household income, ethnic origin, diabetes, BMI, smoking status, alcohol consumption, diet, physical activity, and amount of cadmium in urine.