A population-based study in New Zealand examined the effects of childhood lead exposure at age 11 and again at age 38. The degree of lead exposure was determined to be inversely correlated with IQ levels and socioeconomic advancement.
In the wake of Flint Michigan, lead poisoning has made its way into the media spotlight. Despite past efforts to ban lead from paint and gasoline, pollutants such as lead can also make their way into drinking water through other avenues such as antiquated plumbing. While it is generally accepted that lead exposure can cause adverse mental and developmental consequences in children, it was previously unknown if childhood lead exposure effects would follow individuals into adulthood. A groundbreaking longitudinal study by Reuben and colleagues recently published in Journal of the American Medical Association tackled such questions.
In this prospective cohort study, researchers used data collected from 1037 participants born between 1972 and 1973. These participants were distributed across diverse socioeconomic backgrounds. Of the original participants, 565 had been tested for lead exposure at age 11. These 533 participants were followed up with again at age 38 and were administered an IQ test called the Wechsler Adult Intelligence Scale-IV. This test examined working memory, processing speed, perceptual reasoning, and verbal comprehension. 541 of the original participants were also rated using the New Zealand Socioeconomic Index which ranges from a score of 10 as the lowest, and a score of 90 as the highest.
The researchers found that the participants with childhood lead exposure scored lower than those negative to lead exposure, as seen in the IQ subcategories of working memory, and perceptual reasoning. The participants did not show significant differences in their processing speed or verbal comprehension. It was also determined that the higher the degree of lead exposure, the more significant the decrease in the aforementioned IQ subcategories, with a 1.26 point lower working memory score per every 5-µg/dL increase in blood lead levels, and a 1.61 point lower perceptual reasoning score per every 5-µg/dL increase in blood lead levels. Furthermore, a 1.79 point lower score in the New Zealand Socioeconomic Index was determined per every 5-µg/dL increase in blood lead levels.
This study is significant because it gives insight into the long-term effects of lead poisoning, not only within the realm of cognitive functioning but also as it relates to the ability to climb socioeconomically. One strength of this study is that it included a broad population with respect to maternal IQ scores and socioeconomic ranking, and made adjustments for such differences via calculations. A limitation of this study is that the majority those positive for lead exposure demonstrated clinically high blood-lead levels, and may not be as relative to those with very low levels of lead exposure.
Written By: Allison Pitman Sevillano, MS, PT, DPT