Long-term lead exposure may harm the brain: study

Reuters Health
Tuesday, September 19, 2006
By Anthony J. Brown, MD

NEW YORK (Reuters Health) - Long-term environmental exposure to lead adversely affects cognitive function, and ages the brain by 2 to 6 years, according to the results of a study of relatively healthy older adults.

"Just because lead was removed from industrial, commercial, and residential products in the 1980s, doesn't mean that it didn't have a persistent effect," study chief Dr. Regina A. Shih told Reuters Health.

"We should learn from the example of lead and put policies in place to remove neurotoxicants (from the environment) that are affecting developing brains today," she added.

There has been a great deal of research on the cognitive effects of on-the-job lead exposure, while relatively few studies have looked at the impact of environmental exposure, according to Shih, who is with the Johns Hopkins Bloomberg School of Public Health in Baltimore. "There have been no studies to date that have looked at a diverse population of urban-dwelling older adults."

Her study included 991 subjects, between 50 and 70 years of age, living in 65 contiguous neighborhoods in Baltimore.
Recent lead exposure was estimated by measuring blood levels of the substance, while cumulative exposure was determined by measuring tibia lead. Cognitive function was assessed with standard tests across seven domains of cognitive function including language, processing speed, eye-hand coordination, executive functioning, verbal memory and learning, and visual memory.

The average blood lead level was 3.5 micrograms/dL, while the average tibia level was 18.7 micrograms/g.
Increasing tibia lead levels were associated with significant worsening in all seven cognitive domains, according to the report in the September 13th issue of Neurology.

"The effect of long-term lead exposure on the brain was equivalent to 2 to 6 years of aging," Shih said. "I didn't expect to see such a pervasive effect: all seven domains of cognitive function were impaired," she admitted.

No correlations were seen between blood lead levels and any of the cognitive functions investigated.

In future studies, Shih said her group plans to look at whether lead exposure plays a role in abnormal cognitive aging processes, such as mild cognitive impairment.