A study released this month in The Lancet Public Health is the first to correlate blood lead levels (BLL) of less than 5μg/dL with an increased risk of death from cardiovascular disease. In adults, lead exposure can lead to decreased kidney function and cardiovascular complications such as increased blood pressure and hypertension.
The study used data from the Third National Health and Nutrition Examination Survey between 1988 and 1994, reviewing data from 14,289 adults over the age of 20. They then restricted the pool of participants by selecting only those with blood lead levels of lower than 5 μg/dL. These individuals were then linked to the National Death Index in order to determine an underlying cause of death. In order to account for other variables, the authors assessed confounding variables – diabetes, HDL cholesterol, hypertension, alcohol intake, household income – as well as the effect modification of the relation between concentrations of lead in blood and key factors – sex, age, urban residence, ethnic origin, smoking status and diabetes.
According to the study, “[the] findings suggest that, of the 2.3 million deaths every year in the USA, about 400,000 are attributable to lead exposure”, particularly due to cardiovascular disease and coronary artery disease, also known as ischaemic heart disease. According to the authors, previous studies had assumed that cardiovascular disease was only apparent at concentrations above 5μg/dL and due to this assumption estimated the number of attributable deaths from lead exposure ten times lower.
The researchers highlight the limitations of the study, one being that having only one sample of blood to determine blood lead level and associate this with death decades later has limitations. According to the Agency for Toxic Substances and Disease Registry, close to 94% of the total amount of lead in an adult’s body is stored in the bones and teeth and the authors agree that having a bone sample to supplement the blood samples taken would have been ideal. The researchers state that the lack of this data “might underestimate the contribution of lead exposure to mortality.” On the other hand, it is possible that the study’s result might be an overestimation of the effects of lead in blood since the study could not exclude the residual confounding effects from socioeconomic and occupational factors.
The authors conclude that “although reducing the amount of lead in blood might cut a patient’s risk of cardiovascular disease mortality, it is more accurate to view this study as estimating how many deaths might have been prevented if historical exposures to lead hadn’t occurred,” then to directly attribute it to deaths occurring today. This study gives additional evidence to support the need to continue reducing lead exposure to the population as a whole, both children and adults, and has highlighted for the first time the impact of low-levels of exposure, i.e., levels at or below blood lead levels of 5 μg/dL.