Lead exposure, even at low levels, might increase an individual's risk of death—and might account for a far greater number of annual deaths than previously estimated, according to a study in The Lancet.
Previous research has demonstrated a link between lead exposure and high blood pressure and cardiovascular disease. However, the researchers said this is the first study to estimate the number of U.S. deaths associated with low levels of lead exposure with a nationally representative sample.
For the study, researchers examined the health data of more than 14,000 U.S. adults ages 20 and older who participated in CDC's Third National Health and Nutrition Examination Survey between 1988 and 1994. The researchers focused on concentrations of lead in blood, cadmium in urine, and other relevant covariates among the participants. In 2011, the researchers checked participants' living status in the National Death Index.
The researchers found 4,422 of the 14,289 U.S. adults examined had died by 2011, and approximately 18% of those deaths could have been prevented if individuals had reduced their blood-lead concentrations to 1.0 per deciliter.
Based on those findings, the researchers estimated 412,000 deaths annually could be linked to lead exposure—more than 10 times the amount previously estimated. Of those deaths:
- 256,000 could be attributed to cardiovascular disease; and
- 185,000 could be attributed to ischemic heart disease.
The researchers found every level of lead exposure posed a health risk, but those with the highest level of exposure had the greatest risk. For instance, the researchers found individuals who had an initial blood lead concentration at the 90th percentile—or 6.7 micrograms per deciliter—had a 37% increase in their all-cause mortality and a 70% increase in their cardiovascular disease morality when compared with individuals who had an initial blood level concentration at the 10th percentile—or 1.0 micrograms per deciliter.
CDC recommends public officials address blood lead concentrations above five micrograms per deciliter, but cautions that no safe levels of lead in the blood have been identified, CNN reports.
The researchers concluded, "Low-level environmental lead exposure is an important, but largely overlooked, risk factor for cardiovascular disease mortality in the [United States]." They added, "A comprehensive strategy to prevent deaths from cardiovascular disease should include efforts to reduce lead exposure."
Bruce Lanphear, a lead author on the study and a professor of health sciences at Simon Fraser University, said the study's findings suggest "[t]here's no safe threshold" of lead exposure.
Philip Landrigan, dean for Global Health at the Icahn School of Medicine at Mount Sinai who was not involved in the study, said, "The literature has been showing for many years that lead causes hypertension, stroke, and cardiovascular disease," but "[t]his study now shows that the cardiovascular toxicity of lead extends down to lower levels than were previously examined." Landrigan said, "My guess is that internists and family doctors who are caring for adults are, after the publication of this study, going to think more about lead as a risk factor for heart disease."
However, Howard Hu, a professor of environmental public health at the University of Toronto who was not involved in the study, said the new research could face "a lot of critical interpretation and skepticism." Hu noted that the study used standard methods to account for other risk factors, but "[t]here are some things that one could argue could be measured better, like socioeconomic status, and they acknowledged that there might still be some undetected influence of socioeconomic status."
For his part, Lanphear acknowledged that one of study's main limitations is that it relied on a single blood concentration measurement that had been taken at the beginning of the study period—but that the limitation suggests the number of annual deaths related to lead exposure could be even higher. Lanphear said, "Our reliance on a single blood test as opposed to serial blood tests means that we have underestimated the impact of lead exposure on cardiovascular disease" (James, The Desert Sun/USA Today, 3/13; Bharanidharan, "The Grapevine," Medical Daily, 3/13; Lieber, CNN, 3/12; Lanphear et al., The Lancet, 3/12).
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