Lead on the Brain

A study published in the Journal of Neuroscience last week reports a link between lead exposure and accumulation of Alzheimerâs-type plaque in the brains of primates. The National Institutes of Health-funded study examined the brain tissues of 23-year-old monkeys that had been exposed to lead for the first 400 days of their lives (resulting in blood lead levels of 19â26 µg/dl, but no overt signs of toxicity), and found that they had elevated expression of Alzheimerâs-related genes as well as altered levels, characteristics, and distribution of amyloid plaques, which are one of the hallmarks of Alzheimerâs Disease.

The studyâs lead researcher, Dr. Nasser Zawia of the University of Rhode Island, told the Providence Journal that the research is significant because, while heâs found similar results in mice and rats, this is the first time scientists have found the lead-Alzheimerâs link in primates. Zawia and a spokesperson for the Alzheimerâs Association put the results in context for people worried about their own disease risk:

Zawia and a spokesman for the national Alzheimerâs Association cautioned that the study should not prompt lead-poisoning victims or their families to fear that their lead exposure will automatically lead to Alzheimerâs.

Until the last few years, Rhode Island has been a hot bed of lead poisoning. More than 30,000 children have been diagnosed with elevated lead levels since 1991.

âI would say itâs just another factor, another risk factor,â Zawia said in a telephone interview. âItâs like how smoking is a risk factor for cancer. It puts you at greater risk. But there are 100 other things that can intervene between early life and old age. And this does not just apply to lead. Certain other things may lay dormant for many years.â

William H. Thies, vice president of medical and scientific relations at the Alzheimerâs Association in Chicago, called the study âgood, solid basic science,â but he also emphasized âmaking a leap from this paper to saying Alzheimerâs disease is caused by early childhood lead exposures doesnât fit.â

Thies recalled that in the past some people pinpointed aluminum as a cause of Alzheimerâs and many people threw away their aluminum pots and pans before that theory was rejected.

âI predict weâll find no single, monolithic cause,â said Thies. âWe know there are already lots of good reasons for removing lead from the environment. And itâs certainly possible lead is a contributor to Alzheimerâs. But I donât think itâs the answer to solving Alzheimerâs.â

Since we already know that lead poisoning causes serious neurological problems in children â and that even elevated blood-lead levels below the official cutoff are cause for concern â health officials are already motivated to reduce lead exposure, and this finding may not have much effect on prevention efforts. Itâs an important reminder, though, that the substances weâre putting in our environment today might have health effects that wonât become apparent until decades into the future.