Lead-associated mortality in the US 1999-2020: a time-stratified analysis of a national cohort

Objectives: We undertook time-stratified analyses of the National Health and Nutrition Examination Survey in the US to assess time trends (1999-2020) in the associations of blood lead (BL) with blood pressure, mortality, the BL-associated population attributable fraction (PAF). Methods: Vital status of participants, 20-79 years old at enrolment, was ascertained via the National Death Index. Regressions, mediation analyses and PAF were multivariable adjusted and standardized to 2020 US Census data. Results: In time-stratified analyses, BL decreased from 1.76 mu g/dl in 1999-2004 to 0.93 mu g/dl in 2017-2020, while the proportion of individuals with BL < 1 mu g/dl increased from 19.2% to 63.0%. Total mortality was unrelated to BL (hazard ratio (HR) for a fourfold BL increment: 1.05 [95% confidence interval, CI: 0.93-1.17]). The HR for cardiovascular death was 1.44 (1.01-2.07) in the 1999-2000 cycle, but lost significance thereafter. BL was directly related to cardiovascular mortality, whereas the indirect BL pathway via BP was not significant. Low socioeconomic status (SES) was directly related to BL and cardiovascular mortality, but the indirect SES pathway via BL lost significance in 2007-2010. From 1999-2004 to 2017-2020, cardiovascular PAF decreased (P < 0.001) from 7.80% (0.17-14.4%) to 2.50% (0.05-4.68%) and number of lead-attributable cardiovascular deaths from 53 878 (1167-99 253) to 7539 (160-14 108). Conclusion: Due to implementation of strict environmental policies, lead exposure is no longer associated with total mortality, and the mildly increased cardiovascular mortality is not associated with blood lead via blood pressure in the United States.