"Safe" Lead Levels Linked to Depression, Panic in Young Adults

Janis C. Kelly

December 09, 2009

December 9, 2009 — Young adults with higher blood lead levels are more likely to have major depressive disorder (MDD) or panic disorder, even if they have exposure to lead levels generally considered safe, new research suggests.

Maryse F. Bouchard, PhD, Universite de Montreal, Quebec, Canada, and Harvard School of Public Health, Boston, Massachusetts, and colleagues found individuals with lead levels of 2.11 μg/dL or more had 2.3 times the odds of having MDD and nearly 5 times the odds of panic disorder compared with those with lead levels of 0.7 μg/dL or less.

"What is most surprising is the finding that lead can be associated with adverse mental health status at such low levels of exposure," Dr. Bouchard told Medscape Psychiatry. The mean blood level in study subjects was 1.61 μg/dL.

The study is published in the December issue of Archives of General Psychiatry.

The investigators analyzed data from 1987 adults aged 20 to 39 years who were participants in the National Health and Nutrition Examination Survey between 1999 and 2004. Participants underwent medical examinations that included collection of a blood sample and also completed a diagnostic interview to identify MDD, panic disorder, and generalized anxiety disorder.

The number of individuals who met diagnostic criteria for MDD was 134 (6.7%), 44 (2.2%) had panic disorder, and 47 (2.4%) had generalized anxiety disorder.

Because smoking is related to blood lead levels, the researchers conducted additional analyses excluding the 628 smokers. Among nonsmokers, the elevation in risk between the highest and lowest blood lead levels was increased to 2.5-fold for MDD and 8.2-fold for panic disorder.

Need to Reduce Environmental Exposure

Previous studies conducted in highly exposed employees from foundries, smelters, and battery plants show that these workers (who had blood lead levels averaging 40 μg/dL) have reported elevated symptoms of depression, hostility, and anxiety, said Dr. Bouchard.

A study conducted in nonoccupationally exposed older men showed that those with higher blood lead levels (averaging 6.3 μg/dL) also had a higher prevalence of self-reported anxiety, phobic anxiety, and depression. "In my study group, the mean blood lead level was only 1.6 μg/dL, which is representative of the exposure level in the general population,” Dr. Bouchard said.

Eliminating lead from gasoline has decreased average blood lead levels in the general population, but remaining sources of exposure include paint, industrial processes, pottery, and contaminated water.

However, Dr. Bouchard pointed out that blood lead levels reflect not only current exposure but also past exposures because lead is sequestered in bones and is slowly released into the blood.

"These findings suggest that lead neurotoxicity may contribute to adverse mental health outcomes, even at levels generally considered to pose low, or no, risk," the researchers conclude. "These findings, combined with recent reports of adverse behavioral outcomes in children with similarly low blood lead levels, should underscore the need for considering ways to further reduce environmental lead exposures," they write.

Dose-Response Relationship Questioned

Edwin van Wijngaarden, PhD, interim chief of the Division of Epidemiology, Community & Preventive Medicine at the University of Rochester in New York, reviewed the study for Medscape.

"Although the data reported by Bouchard et al are certainly suggestive of an association between blood lead levels and major depressive disorder, the nature of the dose-response relationship is somewhat uncertain, with no clear pattern until the upper quintile.

"The authors emphasize the statistically significant trend statistics, which are appropriate if there is a true linear trend — not sure if that is the case here. The results for panic disorder and generalized anxiety disorder suffer from limited statistical power and consequently statistically imprecise risk estimates, and I would be cautious interpreting the dose-response patterns reported for these outcomes," he said.

Dr. van Wijngaarden also noted that the mental health outcomes studied were only available for adults aged 20 to 39 years and might differ for older adults with higher levels of cumulative lead exposure.

Dr. van Wijngaarden and colleagues recently examined population-based data on blood lead levels in relation to depression in the United States in a study that will be published in the near future.

This study was supported by the Canadian Institutes for Health Research and the National Institute of Environmental Health Sciences. Dr. Bouchard and Dr. van Wijngaarden have disclosed no relevant financial relationships.

Arch Gen Psychiatry. 2009;66:1313-1319.

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