Exposure to Lead May Contribute to Cognitive Decline Years Later
> 1/28/2008 1:47:00 PM

Over the past few years, researchers have questioned the role played by lead in natural cognitive decline. Past studies have demonstrated that exposure to toxins can have lifelong ramifications, and some researchers now believe that exposure to lead early in life contributes to mental decline during old age.

In 2006, a team of researchers, led by Dr. Brian Schwartz, studied the effects of lead exposure in nearly 1,000 Baltimore residents between the ages of 50 and 70. The researchers measured lead levels in the subjects' blood and in their shinbones. While lead levels in the blood indicate recent exposure to lead, lead levels in bone indicate cumulative exposure to lead over the course of a lifetime. The researchers then assessed various areas of the subjects' cognitive abilities, including their language skills and memory. Those with higher bone lead levels performed poorly in all areas of cognition, and these results remained significant when the researchers controlled for other factors that may have affected the subjects' cognitive functioning. The researchers found no association between blood lead levels and cognition, an indication that the effects of lead on cognition may not become evident until years or even decades after exposure.

Last year, Dr. Schwartz published an analysis of three separate longitudinal studies that provided further evidence of the link between cognition and lead exposure. One of these studies focused on 1,140 Baltimore residents between the ages of 50 and 70. The other two studies included 1,109 former workers from a U.S. lead manufacturing factory and 803 workers from an industrial area of Korea. In all three studies, examination of the subjects' shinbones revealed a consistent association between high bone lead levels and deficient cognitive functioning. By performing MRI scans on the American factory workers, the researchers also found that those with high bone lead levels also had less brain volume.

Much as been done to reduce our exposure to toxins over the past few decades. The amount of lead Americans are exposed to fell dramatically when leaded gasoline was phased out, beginning in 1976, and when paint containing a harmful amount of lead was outlawed in 1978. Since the late 1970s, the average amount of lead in the blood of American adults has fallen, and by 1990 the amount had been reduced by 80%. Despite these trends, lead exposure remains a problem, especially for workers in certain occupations and for children, whose brains are particularly vulnerable to the effects of lead. In 2002, 310,000 children between the ages of 1 and 5 had blood lead levels higher than what the CDC considers safe. These numbers represent a large improvement over past decades, when millions of children had elevated blood lead levels, but we must continue working to reduce lead exposure and protect those who are most at risk. While exposure to lead is not the only factor that may contribute to diminished cognitive abilities, it is a risk factor that we have some control over. By working to create an environment free of lead, we can help prevent the physical and mental symptoms that lead exposure can create.

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