The study examined 532 former employees of a chemical manufacturing plant who had not been exposed to lead for an average of 18 years. The workers had worked at the plant for an average of more than eight years.
The researchers measured the amount of lead accumulated in the workers' bones and used MRI scans to measure the workers' brain volumes and to look for white matter lesions, or small areas of damage in the brain tissue.
The higher the workers' lead levels were, the more likely they were to have smaller brain volumes and greater amounts of brain damage. A total of 36 percent of the participants had white matter lesions. Those with the highest levels of lead were more than twice as likely to have brain damage as those with the lowest lead levels. Those with the highest levels of lead had brain volumes 1.1 percent smaller than those with the lowest lead levels.
"The effect of the lead exposure was equivalent to what would be expected for five years of aging,"said study author Walter F. Stewart, PhD, of the Center for Health Research of the Geisinger Health System in Danville, PA, and the Johns Hopkins Bloomberg School of Public Health in Baltimore, MD.
Stewart said the results confirm earlier findings in this same population that people with occupational lead exposure experience declines in their thinking and memory skills years after their exposure. "The effect of lead on the brain is progressive," Stewart said. "These effects are the result of persistent changes in the structure of the brain, not short-term changes in the brain's neurochemistry."