Greater environmental lead exposure in adults -- even at levels generally considered to pose little or no risk -- was associated with an increased likelihood of depression and panic disorder, a cross-sectional survey found.
Logistic regression analyses showed that patients whose blood levels of lead were in the highest quintile had 2.3 times the odds of major depressive disorder (95% CI 1.13 to 4.75) and 4.9 times the odds of panic disorder (95% CI 1.32 to 18.48) compared with those in the lowest quintile, according to Maryse F. Bouchard, PhD, of the University of Montreal in Quebec, and colleagues.
Action Points
- Explain to interested patients that exposure to lead, even at low levels, may increase their chances of developing depression or panic disorder.
- Also explain that the levels of lead in the environment have declined during the past three decades, with the removal of lead from gasoline, but that significant sources remain, including in deteriorating water pipes.
- Point out that the design of the study does not allow determination of causality.
However, higher blood levels were not associated with a greater likelihood of generalized anxiety disorder, the researchers reported in the December issue of Archives of General Psychiatry.
Lead is a ubiquitous neurotoxicant, and despite marked declines in blood levels over the past three decades -- largely because of the removal of lead from gasoline -- significant sources of exposure remain, such as in industry and in deteriorating water pipes.
Most research into the neurotoxic effects of lead have focused on prenatal and early-life exposures, and on very high level occupational exposures, where workers have reported neuromotor, cognitive, and mood disorders.
But little is known about the effects of lead exposure at levels commonly experienced by adults, so the researchers analyzed data from the National Health and Nutrition Examination Survey (1999 to 2004) to investigate the relationship between blood levels of lead and psychological disorders.
Of the 1,987 adults ages 20 to 39 included in the sample, 134 (6.7%) met the DSM-IV criteria for major depressive disorder, 44 (2.2%) met the criteria for panic disorder, and 47 (2.4%) met the criteria for generalized anxiety disorder.
Blood levels were analyzed in quintiles, with the lowest being ≤0.7 μg/dL and the highest being ≥2.11 μg/dL.
After adjustment for sex, age, race/ethnicity, education, and poverty-to-income ratio, increasing blood lead levels were associated with greater odds of major depression (P=0.05 for trend) and panic disorder (P=0.02 for trend), but not for generalized anxiety disorder (P=0.78).
Characteristics associated with the risk of these disorders were sex and race/ethnicity (P<0.01 for both), but not age, education status, or poverty-to-income ratio.
Mexican-Americans had the highest blood lead levels but the lowest rates of depression and panic disorders, and men had higher lead levels and lower rates of the disorders than women.
When the odds were evaluated on a continuous log10 transformed scale, higher blood levels again were associated with increased odds. For each doubling of blood lead level, the odds ratio for major depressive disorder was 1.19 (95% CI 0.93 to 1.53, P=0.16) and the odds ratio for panic disorder was 1.44 (95% CI 1.02 to 2.03, P=0.04).
Because smoking has been linked with both blood lead levels and psychiatric disorders, the investigators also conducted sensitivity analyses excluding the 628 current smokers, and found slightly higher odds ratios for major depression, at 2.93 (95% CI 1.24 to 6.92, P=0.03 for trend) for the highest quintile.
In this model there also was a significant association between higher blood levels and greater odds of panic disorder (OR 9.57, 95% CI 1.28 to 71.43, P=0.01 for trend), but the wide confidence interval related to the small number of only 14 cases.
As to how lead exposure might contribute to the etiology of these disorders, the researchers suggested that "perturbation of neurochemical processes," such as disruptions of catecholaminergic systems, could be involved.
"Investigations on how low lead exposure disrupts neurochemical processes could provide insights into the mechanisms of depressive and anxious states," they wrote.
Among the study's limitations are its cross-sectional design and the possibility of bias from uncontrolled confounders.
Current methods of measuring blood levels of lead also reflect lead sequestered in bone, possibly from past exposures during critical periods of development, "which would be consistent with neurodevelopmental hypotheses of mood and anxiety disorders."
The finding of a link between even low-level lead exposure and two common disorders that are associated with substantial morbidity underscores the need for continued efforts to decrease environmental exposures, the researchers concluded.
Disclosures
The study was funded by the Canadian Institutes for Health Research and the National Institute of Environmental Health Sciences.
No financial disclosures were reported.
Primary Source
Archives of General Psychiatry
Bouchard M, et al "Blood lead levels and major depressive disorder, panic disorder, and generalized anxiety disorder in US young adults" Arch Gen Psychiatry 2009; 66: 1313-19.