In a recent study published in Journal of the American Heart Association, a group of researchers evaluated the association between declines in blood lead levels and changes in both systolic and diastolic blood pressure in adult American Indian participants of the SHFS (Strong Heart Family Study).
Study: The Contribution of Declines in Blood Lead Levels to Reductions in Blood Pressure Levels: Longitudinal Evidence in the Strong Heart Family Study. Image Credit: kurhan/Shutterstock.com
Background
United States (US) regulations, such as banning lead in various products and controlling its levels in water and air, have significantly lowered lead exposure and its resultant health risks. Still, disparities in exposure exist among different racial and ethnic groups.
Lead is a known risk factor for cardiovascular diseases. Studies, including the National Health and Nutrition Examination Survey (NHANES), have shown that decreasing blood lead levels in the US correlate with reduced cardiovascular disease deaths.
Lead's adverse effects on blood pressure and heart function are well-documented, particularly at high exposure levels. However, the impact at current, lower exposure levels is less clear.
Further research is needed to fully understand the long-term health impacts of low-level lead exposure and develop targeted strategies for prevention and treatment.
About the study
The Strong Heart Study (SHS), involving over 4,500 American Indian adults from multiple tribes, was initiated to explore cardiovascular diseases and their risk factors.
Participants, aged between 45 and 74 at the study's outset were re-examined across several phases. The SHFS extended this research to include multigenerational cohorts.
This analysis focused on participants who provided blood samples during the third and fifth phases of the study. From these, 285 participants were selected for blood lead measurement.
This selection aimed to ensure gender balance and adequate sample volume. The study compared blood lead levels using samples analyzed at two different laboratories, finding no significant differences in the results.
Blood pressure was measured using standard procedures by trained personnel, and hypertension was defined based on specific criteria. Cardiac geometry and function were assessed via transthoracic echocardiograms, providing detailed insights into the heart's structure and performance.
Participants' socio-demographic, lifestyle, and health information was carefully collected, ensuring the reliability of the data. The study also considered various health markers, including glucose, cholesterol, and kidney function.
The statistical analysis, performed using R, investigated the relationship between blood lead level decline and changes in blood pressure and cardiac metrics. The study accounted for age, education, sex, body mass index, and smoking status.
The analysis explored potential dose-response relationships and non-linear associations, offering a comprehensive understanding of the impact of lead exposure on cardiovascular health.
Study results
The present study involving 285 participants measured blood lead levels during two distinct phases. The demographic composition of these participants in Phase 3 closely resembled the broader study group regarding body mass index, gender distribution, blood pressure, and smoking status.
The average age was 51.5 years. The study categorized participants based on the extent of their blood lead level decline, revealing significant variations in baseline blood lead concentrations across these categories.
The highest decline in blood lead levels was noted in the tertile with the largest decrease (>0.91 μg/dL), averaging 1.78 μg/dL. Notably, participants in this tertile were predominantly male, had lower instances of hypertension, and had lower baseline fasting glucose levels.
The analysis revealed a correlation between the decrease in blood lead and the reduction in systolic blood pressure. Specifically, participants in the tertile with the most significant lead reduction exhibited a notable decline in systolic blood pressure, with a mean difference of -7.08 mm Hg.
This correlation appeared more pronounced after adjusting for baseline fasting glucose and dyslipidemia. However, this trend did not manifest as a linear association in the flexible cubic spline model analysis.
The relationship between lead reduction and blood pressure changes became more apparent only when the decline in blood lead exceeded 0.1 μg/dL.
The study also examined changes in other cardiac metrics. Notably, a decline in blood lead was significantly associated with decreased interventricular septum thickness.
Additionally, an increase in transmitral early filling velocity was observed, but this was limited to the highest levels of blood lead decline, where the sample size was small.
Several sensitivity analyses included varying the consideration of participants’ hypertension status and adjusting for baseline income needs.
The results consistently indicated a similar direction and strength in the relationships between blood lead changes and blood pressure outcomes as observed in the main models, suggesting a potential link between reduced blood lead levels and improved cardiovascular health.
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