Lithium in Drinking Water and Thyroid Function

BACKGROUND: High concentrations of lithium in drinking water were previously discovered in the Argentinean Andes Mountains. Lithium is used worldwide for treatment of bipolar disorder and treatment-resistant depression. One known side effect is altered thyroid function. OBJECTIVES: We assessed associations between exposure to lithium from drinking water and other environmental sources and thyroid function. METHODS: Women (n = 202) were recruited in four Andean villages in northern Argentina. Lithium exposure was assessed based on concentrations in spot urine samples, measured by inductively coupled plasma mass spectrometry. Thyroid function was evaluated by plasma free thyroxine (T(4)) and pituitary gland thyroid-stimulating hormone (TSH), analyzed by routine immunometric methods. RESULTS: The median urinary lithium concentration was 3,910 μg/L (5th, 95th percentiles, 270 μg/L, 10,400 μg/L). Median plasma concentrations (5th, 95th percentiles) of T(4) and TSH were 17 pmol/L (13 pmol/L, 21 pmol/L) and 1.9 mIU/L, (0.68 mIU/L, 4.9 mIU/L), respectively. Urine lithium was inversely associated with T(4) [β for a 1,000-μg/L increase = −0.19; 95% confidence interval (CI), −0.31 to −0.068; p = 0.002] and positively associated with TSH (β = 0.096; 95% CI, 0.033 to 0.16; p = 0.003). Both associations persisted after adjustment (for T(4), β = −0.17; 95% CI, −0.32 to −0.015; p = 0.032; for TSH: β = 0.089; 95% CI, 0.024 to 0.15; p = 0.007). Urine selenium was positively associated with T(4) (adjusted T(4) for a 1 μg/L increase: β = 0.041; 95% CI, 0.012 to 0.071; p = 0.006). CONCLUSIONS: Exposure to lithium via drinking water and other environmental sources may affect thyroid function, consistent with known side effects of medical treatment with lithium. This stresses the need to screen for lithium in all drinking water sources.