Abstract
BackgroundMercury is a neurotoxicant linked with psychiatric symptoms at high levels of exposure. However, it is unclear whether an association is present at the low exposure levels in the US adult population.Materials and MethodsCross-sectional associations of total blood mercury and depression were assessed in 6,911 adults age ≥20 in the National Health and Nutrition Examination Survey (NHANES), 2005–2008. The Patient Health Questionnaire-9 was used to assess depression (high likelihood of a depressive spectrum disorder diagnosis; score 5–27).ResultsUnadjusted survey weighted logistic regression suggested that higher total blood mercury was associated with lower odds of depression (Odds Ratio = 0.49, 95% Confidence Interval: 0.36–0.65, comparing the highest and lowest mercury quintiles). This association largely disappeared after adjustment for sociodemographic variables (income-poverty ratio, education, marital status). However, in age-stratified analyses, this inverse relationship remained in older adults (age ≥40) even after adjustment for sociodemographic variables. Simulation analyses adjusting for expected confounding effects of fish intake suggested that the inverse relationship among older adults may be plausibly attributed to residual confounding (Odds Ratio = 0.75, 95% Confidence Interval: 0.50–1.12, comparing the highest and lowest mercury quintiles).ConclusionsHigher total blood mercury was not associated with increased odds of depression. The lower odds of depression in older adults with higher total blood mercury may be due to residual confounding.
Highlights
Mercury in its various elemental and compound forms is a ubiquitous neurotoxin, with many different potential routes for human exposure, including air pollution, dental amalgams, fish consumption, and occupational settings.[1,2] Exposure to high levels of mercury may increase the risk of psychiatric symptoms.[3,4] For instance, residents of Minamata, Japan, an area with large-scale methylmercury pollution, exhibited increased levels of mood and behavioral dysfunction, compared to residents of a reference area.[5]
Unadjusted survey weighted logistic regression suggested that higher total blood mercury was associated with lower odds of depression (Odds Ratio = 0.49, 95% Confidence Interval: 0.36–0.65, comparing the highest and lowest mercury quintiles)
Simulation analyses adjusting for expected confounding effects of fish intake suggested that the inverse relationship among older adults may be plausibly attributed to residual confounding (Odds Ratio = 0.75, 95% Confidence Interval: 0.50–1.12, comparing the highest and lowest mercury quintiles)
Summary
Mercury in its various elemental and compound forms is a ubiquitous neurotoxin, with many different potential routes for human exposure, including air pollution, dental amalgams, fish consumption, and occupational settings.[1,2] Exposure to high levels of mercury may increase the risk of psychiatric symptoms.[3,4] For instance, residents of Minamata, Japan, an area with large-scale methylmercury pollution, exhibited increased levels of mood and behavioral dysfunction, compared to residents of a reference area.[5]. While mercury is well-recognized as a neurotoxin, an association between high levels of mercury exposure and risk of depression does not necessarily mean that low levels of exposure carry a risk as well. Investigating possible health effects of low-level mercury exposure is important, especially given recent debate concerning regulations for mercury emissions in the U.S, and heightened public health awareness concerning mercury. Mercury is a neurotoxicant linked with psychiatric symptoms at high levels of exposure. It is unclear whether an association is present at the low exposure levels in the US adult population
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