Lead exposure on the job can cause progressive declines in memory and learning abilities nearly two decades later, researchers found in a study of long-term side effects of lead exposure on adults.
The new study is published in the Oct. 25 issue of Neurology, the scientific journal of the American Academy of Neurology.
The study compared 535 former chemical manufacturing employees exposed to lead at work with 118 nonexposed people from the same neighborhoods. Exposed workers in the study appeared up to five years older than their real ages.
"The effects of the average level of bone lead found in former lead workers was like five more years of aging on the brain," said study author Dr. Brian Schwartz of the Johns Hopkins School of Hygiene and Public Health in Baltimore.
Over the course of four years, study participants were followed undergoing two to four sets of neurological tests with an average of one year''s time in between tests. On average, the workers had been exposed to lead 16 years before the study.
During the first year of the study, lead levels were determined through blood tests, while follow-up visits measured lead levels in bone through a technique called X-ray fluorescence.
"The higher the peak level of lead determined in former lead workers, the greater the decline in brain functions," Schwartz said. "Since these declines were seen long after exposure to lead had stopped, it suggests that the effect of lead on the brain is progressive."
The workers not only had greater declines in test scores due to lead exposure, but also in normal age-related declines in brain functions, Schwartz said.
Significant differences were discovered between the former workers and other participants in tests of visual construction, verbal memory and learning, visual memory, planning and organizational ability, and manual dexterity.
"We know there''s a decline in brain power as we get older; generally, we call this ''normal aging,''" Schwartz said. "Most of the research has been about how chemicals, like lead, affect kids. This is the first study to explore long-term problems caused by exposure to chemicals as adults."
Of course, most people are not exposed to high levels of lead at work, but these findings may be relevant to the general population, pending the results of research under way, according to Schwartz. "Some of what we have been calling ''normal aging'' may, in fact, be due to past exposure to chemicals or other agents that can affect the central nervous system. This is potentially a very important health problem."
by Virginia Sutcliffe