Study for Promotion of Health in Recycling Lead – Rationale and design

Abstract

The Study for Promotion of Health in Recycling Lead (SPHERL) will enroll 500 newly hired workers, whose blood lead during 2 years of follow-up is expected to increase from levels less than 2 μg/dl, as currently observed in the US population, to 20-30 μg/dl. The main outcome variables to be studied are (i) blood pressure (BP) analyzed as a continuous or categorical variable, both cross-sectionally and longitudinally, and using conventional and ambulatory BP measurement; (ii) indexes of glomerular and tubular renal function, (iii) heart rate variability analyzed in the frequency domain as measure of autonomous sympathetic modulation, (iv) peripheral nerve conductivity velocity, (v) neurocognitive performance, and (vi) quality of life. Expected outcomes. Assuming a 10-fold increase in blood lead, SPHERL will have sufficient statistical power to detect over 2 years a steepening of the age-related rise in systolic BP from 1 to 5 mmHg and a doubling of the age-related decline in the estimated glomerular filtration rate from 3.5 to 7.0 ml/min/1.73 m(2). The longitudinal design of our study complies with the temporality principle of the Bradford-Hill criteria for assessing possible causality between outcomes and exposure. SPHERL will attempt to resolve the apparent contradiction between general population studies showing associations between adverse health effects and low lead exposure with blood lead levels below 5 μg/dl and studies conducted in occupational cohorts indicating that adverse effects of lead exposure occur at much higher blood lead levels.

Neurocognitive function in relation to blood lead among young men prior to chronic occupational exposure

“…SPHERL is a longitudinal study of newly hired lead workers at battery manufacturing and lead recycling plants in the United States (18), which complies with the Helsinki declaration for investigations in humans (19). The Ethics Committee of the University Hospitals Leuven (Belgium) approved the study protocol.…”

“…We therefore reassessed the association of neurocognitive function with blood lead, using the baseline measurements (2015-2017) collected in the ongoing Study for Promotion of Health in Recycling Lead (SPHERL; NCT02243904). Study participants were young men (mean age, 28.6 years), examined prior to chronic occupational exposure at lead recycling plants in the United States (18).…”

Central hemodynamics in relation to blood lead in young men prior to chronic occupational exposure

“…Study design and study population SPHERL (NCT02243904) is a longitudinal study of newly hired lead workers at battery manufacturing and lead recycling plants in the United States [22]. SPHERL complies with the Helsinki declaration for investigations in humans [23].…”

“…Database management and statistical analysis were done using SAS 9.4 software (Carey, NC). The flow and quality control of the data are described in the published protocol [22]. Departure from normality was evaluated using Shapiro-Wilk's statistic.…”

“…We therefore assessed the association of central hemodynamic measurements, including central blood pressure, systolic augmentation, aortic pulse wave velocity and pulse wave reflection, with blood lead, using the first in-study assessment (2015)(2016)(2017) collected in the ongoing Study for Promotion of Health in Recycling Lead (SPHERL; NCT02243904). Study participants were young men examined prior to chronic exposure at lead recycling plants in the United States [22].…”