SAN DIEGO--As if living in the inner city wasn't bad enough. New research shows that the stresses of urban life--a fear of crime, for example--can exacerbate the cognitive problems associated with exposure to lead in older adults.
Numerous studies have shown that in children, high lead levels can harm the kidneys and endocrine system and worsen academic performance. Less work has been done on adults who aren't industrial workers, however. New findings, presented here yesterday at the Society of Toxicology's annual meeting, come from a study of 1140 adults aged 50 to 70 years, who were randomly selected from 65 neighborhoods in Baltimore, Maryland.
To investigate the effects of stress on lead exposure, Thomas Glass, a social epidemiologist at Johns Hopkins Bloomberg School of Public Health in Baltimore, first created a measure of "psychosocial stress." He pulled together a series of indicators, such as crime statistics, number of 911 calls, and complaints about abandoned cars. This measure correlated with salivary levels of cortisol, a stress hormone; residents of rougher neighborhoods tended to have more cortisol.
The researchers then gave a battery of seven cognitive tests to the participants. On three of these tests, the worse the participants fared, the higher their lifelong lead exposure (as indicated by bone lead levels) tended to be. And when the researchers compared these volunteers to other people with the same lead levels, they found that stressed city-dwellers scored lower on these cognitive tests than less-stressed ones. "This is a question of exposure legacy," Glass says, who collaborated with Brian Schwartz and others at Johns Hopkins. "Some part of age-related cognitive decline may be the shadow of childhood lead exposure." In other words, lead exposure early on led to cognitive deficits that persist through life.
Because the effect of lead on cognition appears to be due to lifelong accumulation of the metal, rather than recent acute doses, there is no direct way to lessen exposure. However, the findings do suggest that lessening stress might help mitigate the cognitive decline. "There might be neighborhood interventions that might reduce the impact of exposure," says David Jacobs of the Center for Healthy Housing in Columbia, Maryland.
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