Occupational lead exposure may have long-term effects and dramatically increase the risk of developing Alzheimer's disease in later years, according to research presented during the American Academy of Neurology's 52nd Annual Meeting in San Diego. People who have worked in jobs with high levels of lead exposure are up to 3.4 times more likely to develop Alzheimer's disease.
"Lead exposure remains a major public concern because of its adverse effects on brain development and health in general, even with low exposure levels," said Elisabeth Koss, PhD, study lead author at Case Western Reserve University and University Hospitals of Cleveland, Ohio. "This study suggests that we also need to be concerned because of very long-lasting changes to the nervous system that may increase the risk for Alzheimer's disease.
The study compared the occupational histories of 185 people with Alzheimer's disease to 303 people without Alzheimer's. Utilizing hazard lists developed by the National Occupational Exposure Survey, researchers estimated the probability of toxic exposure to a variety of agents used in each occupation. That occupation exposure was then multiplied by the number of years a person worked at a job to determine lifetime exposure.
In addition to lead, researchers examined exposure to aluminum, copper, iron, mercury, zinc and solvents (a group of chemicals including paint thinners, cleaning fluids and benzene).
Although previous studies have raised concerns about possible relationships between Alzheimer's and many of these metals, including aluminum and solvents, only lead exposure was found to increase the risk of Alzheimer's. The researchers believe that these concerns may have been due to the unrecognized effect of lead as many occupations involve multiple exposures to numerous potentially toxic materials.
"Although lead has long been known to be toxic -- and is believed to have affected the brains of some of the rulers of the Roman Empire, thereby causing its downfall -- its long-term damages are difficult to measure, and thus, the extent of its negative effects have been largely overlooked," said Koss.
In the workplace, people are most often exposed to lead by either breathing lead dust, which is considered to be the most toxic, or by direct skin contact. Activities that can expose workers to lead are 1) smelting or casting lead; 2) removing lead coatings (welding, brazing, cutting, sanding or blasting old paints); 3) heating, machining or spraying lead products, and 4) making lead products (lead--acid battery manufacturing, lead glazing pottery making, cable production, ammunition manufacture, production of lead pipe, cable shielding, electronic components, paint and ink manufacture).
Earlier studies have shown that education has a protective effect against Alzheimer's. As people with less education are more likely to work in blue-collar jobs where there is a greater chance of toxic exposure than white-collar jobs, the researchers statistically adjusted for participants' education levels.
The Alzheimer's patients in the study were also older than those without the disease. Koss noted that this could be related to a decrease in on-the-job toxic exposures due to more recent governmental regulations that enforce relatively safer work conditions.
"Public health efforts have been successful in removing lead from sources, such as gasoline and lead-soldered food and drink cans," commented Koss. "However, we need to remain vigilant about other sources of lead in the home and in the work place, including decaying old paint, contaminated soil or drinking water, hobbies and occupational exposure."
