Major loss of brain cells and damage to the brain tissue is possible in individuals exposed to lead after 18 years. This latest study is available in Neurology, the journal of the American Academy of Neurology, May 23 2006.
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."
The findings raise new questions, according to Andrew S. Rowland, PhD, of the University of New Mexico in Albuquerque, who wrote an editorial accompanying the article. "There have been many studies done on the effects of lead on children's IQ, but the possible effects in other areas, such as attention, aggression, or any mental disorders, have gotten less attention. Exposure to inorganic lead, like that found in paint, remains an important public health problem. And those of us who grew up before the late 1970s still carry high lead levels in our bodies. We need more studies addressing the potential chronic health effects of those exposures."
The study was supported by a grant from the National Institute on Aging.