Environmental exposure to lead: old myths never die – Authors' reply

Wen-Yi Yang and colleagues were troubled that our results1Lanphear BP Rauch S Auinger P Allen RW Hornung RW Low-level lead exposure and mortality in US adults: a population-based cohort study.Lancet Public Health. 2018; 3: e177-e184Summary Full Text Full Text PDF PubMed Scopus (188) Google Scholar contrast with expert opinion and concluded that hypertension is unlikely to explain the current association between concentrations of lead in blood and mortality. They also argued that, because the underlying mechanism of lead is unknown, it precludes preventive strategies and targeted allocation of resources to reduce cardiovascular disease risk. Lead is a causal risk factor for hypertension and coronary (ischaemic) heart disease.2EPA2013 Final report: integrated science assessment for lead. US Environmental Protection Agency, Washington, DCJune, 2013http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=518908Date accessed: June 21, 2018Google Scholar Indeed, the reduction in leaded gasoline might be key to understanding the mysterious decline in deaths from coronary heart disease that began 50 years ago.3Mensah GA Wei GS Sorlie PD et al.Decline in cardiovascular mortality. Possible causes and implications.Circ Res. 2017; 120: 366-380Crossref PubMed Scopus (258) Google Scholar Moreover, there was a precipitous but poorly understood decline in hypertension that was accompanied by a substantial drop in blood lead concentrations following the phase-out of leaded gasoline.4Burt VL Cutler JA Higgins M et al.Trends in the prevalence, treatment and control of hypertension in the adult US population.Hypertension. 1995; 26: 60-69Crossref PubMed Scopus (1159) Google Scholar Hypertension peaked at 36% in US adults from 1976 to 1980 and then declined to 20% by 1988 to 1994, a decline that persisted after adjustment for age, sex, cuff size, body-mass index (BMI), treatment, and smoking.4Burt VL Cutler JA Higgins M et al.Trends in the prevalence, treatment and control of hypertension in the adult US population.Hypertension. 1995; 26: 60-69Crossref PubMed Scopus (1159) Google Scholar The decline in the prevalence of hypertension was coincident with a greater than 80% reduction in median blood lead concentrations among adults, from 13 μg/dL (0·628 μmol/L) in 1976–80, to 3 μg/dL (0·145 μmol/L) in 1988–91 (figure).5Pirkle JL Brody DJ Gunter EW et al.The decline in blood lead levels in the United States: the National Health and Nutrition Examination Surveys.JAMA. 1994; 272: 284-291Crossref PubMed Scopus (728) Google Scholar We should not be surprised that concentrations of lead in blood contribute less to hypertension and cardiovascular disease mortality today. The effect of risk factors, such as lead, should diminish once strategies to reduce exposures are implemented. Importantly, lead was removed from gasoline, paint, and other sources before the underlying mechanisms of lead were fully explicated; it is desirable, but not essential, to know the mechanisms before taking action. As we reported in our Article,1Lanphear BP Rauch S Auinger P Allen RW Hornung RW Low-level lead exposure and mortality in US adults: a population-based cohort study.Lancet Public Health. 2018; 3: e177-e184Summary Full Text Full Text PDF PubMed Scopus (188) Google Scholar we did not find any evidence for effect modification of the relation between concentration of lead in blood with race and ethnicity. Moreover, the design-based statistical methods in NHANES control for clustering of confounders at the primary sampling unit level. Finally, we cited and described numerous lines of evidence linking lead exposure with cardiovascular disease: laboratory studies implicating lead in the development of hypertension and atherosclerosis; prospective cohort studies; a natural history study showing an 18% decline in cardiovascular disease mortality from declining blood lead concentrations; and a reduction in cardiovascular events following chelation therapy. Most epidemics of chronic disease result from the cumulative impact of multiple risk factors, and a comprehensive prevention strategy should address all of them. We declare no competing interests. BPL serves as an expert witness in plaintiff cases of childhood lead poisoning in Milwaukee and Flint, MI, USA, but he receives no personal compensation. Environmental exposure to lead: old myths never dieBased on an analysis of NHANES III, published in The Lancet Public Health (April, 2018), Bruce Lanphear and colleagues1 propose that environmental exposure to lead, even at blood concentrations lower than 5 μg/dL, entails a population-attributable risk of cardiovascular mortality of 37·4%, thereby equalling the risk of smoking. This conclusion contrasts with expert opinion. Based on a comprehensive review of the literature, Navas-Acien and coworkers2 concluded that there is sufficient evidence to infer a causal association of hypertension with lead exposure, but that the evidence is inconclusive to deduce a causal relation of cardiovascular outcomes with lead exposure. Full-Text PDF Open Access

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