Lead exposure well within levels generally considered safe may harm mental health, new research suggests.
Men and women in their 20s and 30s with the highest levels of lead in their blood were more than twice as likely to suffer from major depression as their peers with the lowest blood lead levels, while their risk of panic disorder was nearly five times greater, researchers found.
"This is true for the average American. We are not talking about excessively high exposures, it's just average exposures," Dr. Maryse Bouchard of University of Montreal in Canada and the Harvard School of Public Health in Boston told Reuters Health.
Lead is known to be toxic to the nervous system, Bouchard and her colleagues point out in the Archives of General Psychiatry. But most research on its effects has been done in children and in adults exposed to high levels of the toxic metal on the job.
To investigate whether lead exposure might affect the general population, Bouchard and her team looked at data from the National Health and Nutrition Examination Survey for 1999-2004 on 1,987 men and women 20 to 39 years old. About 7 percent met diagnostic criteria for major depression, while around 2 percent had panic disorder and another 2 percent had generalized anxiety disorder.
Study participants' average blood lead level was 1.61 micrograms per deciliter of blood, and ranged from 0.3 to 37.3 micrograms per deciliter. The higher an individual's blood lead, the greater their risk of depression or panic disorder, but lead levels had no influence on the likelihood of anxiety disorder.
Because smoking cigarettes can increase blood lead levels, Bouchard and her team did a separate analysis of non-smokers, and found similar results.
The Centers for Disease Control and Prevention has stated that blood lead levels of 10 micrograms per deciliter in children "should prompt public health actions," but it has also stated that there is no "safe" blood level in children.
"In the general population, very little research has been done on lead and its potential adverse effects on adults," Bouchard noted.
High levels of lead are known to interfere with the function of neurotransmitters in the brain like serotonin and dopamine, Bouchard added, and this could be the mechanism through which lead exposure might contribute to depression and panic disorder.
One drawback of the study, the researchers note in their report, is that blood lead levels are good for measuring short-term lead exposure, but less accurate for gauging long-term exposure — for this purpose, bone lead tests are more precise.
Nevertheless, they add, blood lead levels do reflect lead from past exposures being released from bone. Another limitation, they add, is the fact that depression or panic disorder might have made people engage in behaviors that would increase their blood levels of lead.
The current findings, the researchers say, suggest that efforts must be made to reduce people's exposure to lead in the environment, for example from tap water contaminated by corroding pipes.
"The solutions are collective," Bouchard said. "We need to enforce banning lead from all the applications that could involve potential exposure for the population."
SOURCE: Archives of General Psychiatry, December 2009.