Total blood mercury levels and depression among adults in the United States: National Health and Nutrition Examination Survey 2005-2008.
BACKGROUND
Mercury 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.


METHODS
Cross-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).


RESULTS
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). 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).


CONCLUSIONS
Higher 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.
Department of Epidemiology and Biostatistics, Drexel University School of Public Health, Philadelphia, Pennsylvania, United States of America.
Tsz Hin H
TH
Ng
Jana M
JM
Mossey
Brian K
BK
Lee
D003430:Cross-Sectional Studies; D003863:Depression / Q000453:epidemiology* / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008628:Mercury / Q000097:blood*; D009749:Nutrition Surveys; D016017:Odds Ratio; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology
D008628:Mercury