In an recent study published in the Journal of the American Heart Association, a group of researchers examined the relationship between a decrease 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).
Due to regulations in the United States, such as the ban of lead in various products and the control of lead levels in water and air, lead exposure and associated health risks have been significantly reduced. However, differences in exposure persist between different races and ethnic groups.
Lead is a known risk factor for cardiovascular disease. Studies, including the National Health and Nutrition Examination Survey (NHANES), have shown that decreasing blood lead levels in the United States are associated with a lower number of deaths from cardiovascular diseases.
The detrimental effects of lead on blood pressure and heart function are well-documented, especially at high exposure levels. However, the effects at current, lower exposure levels are less clear.
Further research is needed to fully understand the long-term health effects of low lead exposure and develop targeted strategies for prevention and treatment.
About the Study
The Strong Heart Study (SHS) involved over 4,500 American Indian adults from various tribes and was designed to investigate cardiovascular diseases and their risk factors.
Participants, who were between 45 and 74 years old at the start of the study, were re-examined in multiple phases. The SHFS extended this research to multi-generational cohorts.
This analysis focused on participants who provided blood samples during the third and fifth phases of the study. From these samples, 285 participants were selected for blood lead measurement.
The aim of this selection was to ensure a balanced gender ratio and an adequate sample size. The study compared blood lead levels based on samples analyzed in two different labs and found no significant differences in the results.
Blood pressure was measured using standard procedures by trained personnel, and hypertension was defined based on specific criteria. Heart geometry and function were assessed using transthoracic echocardiograms, providing detailed insights into the structure and performance of the heart.
Participants‘ sociodemographic, lifestyle, and health information was carefully collected to ensure data reliability. The study also considered various health markers, including glucose, cholesterol, and kidney function.
The statistical analysis conducted using R examined the relationship between the reduction in blood lead levels and changes in blood pressure and cardiac values. The study accounted for age, education, gender, body mass index, and smoking status.
The analysis investigated possible dose-response relationships and nonlinear associations, providing a comprehensive understanding of the effects of lead exposure on cardiovascular health.
In the present study with 285 participants, blood lead levels were measured in two different phases. The demographic composition of these participants in Phase 3 was similar to the broader study group in terms of body mass index, gender distribution, blood pressure, and smoking status.
The average age was 51.5 years. Participants were categorized according to the extent of reduction in blood lead levels, with significant differences in baseline blood lead concentrations observed between these categories.
The greatest reduction in blood lead levels was observed in the tertile with the largest decline (>0.91 μg/dl), averaging 1.78 μg/dl. Notably, participants in this tertile were predominantly male, less likely to have hypertension, and had lower fasting glucose levels.
The analysis revealed an association between the reduction in blood lead levels and the lowering of systolic blood pressure. In particular, participants in the tertile with the greatest lead reduction showed a significant decrease in systolic blood pressure with a mean difference of -7.08 mm Hg.
This correlation appeared more pronounced after accounting for baseline fasting glucose and dyslipidemia. However, this trend did not manifest as a linear relationship in the flexible cubic spline model analysis.
The association between lead reduction and blood pressure changes became clearer when the blood lead decline exceeded 0.1 μg/dl.
The study also investigated changes in other cardiac metrics. Remarkably, a reduction in blood lead levels was significantly associated with a decreased thickness of the interventricular septum.
Furthermore, an increase in early transient filling velocity was observed, but this was limited to the highest levels of blood lead reduction, where the sample size was small.
Several sensitivity analyses included different considerations for participants‘ hypertension status and adjusting for income sufficiency.
The results consistently showed a similar direction and strength of the relationships between blood lead changes and blood pressure outcomes as in the main models, suggesting a potential connection between reduced blood lead levels and improved cardiovascular health.