Environment International 40 (2012) 39–4
Mercury and thyroid autoantibodies in U.S. women, NHANES 2007–2008
Carolyn M. Gallagher, Jaymie R. Meliker
Associations between positive thyroid autoantibodies and total blood mercury in women were evaluated using the National Health and Nutrition Examination Survey (NHANES), 2007–2008. Women are at increased risk for autoimmune disorders, mercury exposure has been associated with cellular autoimmunity and mercury accumulates in the thyroid gland. We used multiple logistic regression to evaluate the associations between total blood mercury and thyroglobulin autoantibody antibody positivity and thyroid peroxidase autoantibody positivity in non-pregnant, non-lactating women aged 20 and older not currently using birth control pills or other hormone therapies, adjusted for demographic factors, menopausal status, nutrient intake and urine iodine (n =2047). Relative to women with the lowest mercury levels (≤0.40 μg/L), women with mercury >1.81 μg/L (upper quintile) showed 2.24 (95% CI =1.22, 4.12) greater odds for thyroglobulin autoantibody positivity (ptrend=0.032); this relationship was not evident for thyroid peroxidase autoantibody positivity. Results suggest an association between mercury and thyroglobulin autoantibody positivity
The heavy metal mercury accumulates in the human thyroid gland, as shown in studies of occupationally exposed workers (Falnoga et al., 2000; Nylander and Weiner, 1991) and industrially exposed residents (Falnoga et al., 2000).
Higher levels of hair mercury, an indicator of organic mercury exposure (ATSDR, 1999), have been associated with detectable antinucleolar autoantibodies, biomarkers of cellular autoimmunity, in a non-occupationally-exposed, ﬁsheating riverine population (Silva et al., 2004). In addition, removal of inorganic mercury-containing dental amalgams resulted in signiﬁcantly decreased levels of the thyroid autoantibodies thyroglobulin antibody (TgAb) and thyroid peroxidase antibody (TPOAb) (Sterzl et al., 2006) suggesting a positive association between mercury and these antibodies.
Thyroglobulin antibody is an antibody against the thyroid protein thyroglobulin, and thyroid peroxidase antibody is directed against thyroid peroxidase, a thyroid enzyme. Elevated levels of thyroid autoantibodies have been observed in patients with autoimmune disorders: TgAb in patients with systemic lupus erythematosus (Lu et al., 2006; Parente et al., 2009; Porkodi et al., 2004) and both TgAb and TPOAb in patients with autoimmune thyroiditis (Baskin, 2006), rheumatoid arthritis (Atzeni et al., 2008; Porkodi et al., 2004), pernicious anemia (Chan et al., 2009), ﬁbromyalgia (Bazzichi et al., 2007; Pamuk and Cakir, 2007) and diabetes (Prazny et al., 2005).
Women are at increased risk for autoimmune disease (Dunaif, 2010) and mortality (Walsh and Rau, 2000). The association between total blood mercury and thyroid autoantibodies, however, has not been evaluated in a U.S. population representative sample of adult women. Therefore, the primary objective of the current study is to examine this relationship in US women.
Studies have also shown that thyroid autoantibodies TgAb and TPOAb are prognostic indicators for long-term risk of hypothyroidism (Li et al., 2008; Vanderpump et al., 1995; Walsh et al., 2010), a disorder of thyroid hormone deﬁciency more prevalent in women and most commonly caused by autoimmune thyroiditis (NIH, 2011). Most recently, Hutﬂess et al. (2011) found increased odds for autoimmune thyroid disease associated with TgAb or TPOAb positivity during the 2–7 years preceding diagnosis. The measurement of thyroid stimulating hormone, or thyrotropin, is the most valuable test to diagnose hypothyroidism and subclinical hypothyroidism, or mildly elevated thyrotropin (Baskin, 2006). Walsh et al. (2010) showed that, among women with baseline thyrotropin levels above 4.0 μIU/ml coincident with TgAb or TPO positivity, the prevalence of hypothyroidism after 13 years was 85.7%. The relationship between mercury exposure and this indicator of autoimmune hypothyroidism risk, however, has not been evaluated in a large, population-representative sample. Therefore, a secondary aim of the current study is to evaluate the association between total blood mercury and elevated thyrotropin coincident with thyroid antibody positivity. A third aim was to evaluate the association between total blood mercury and thyrotropin in US women.
To the best of our knowledge, this is the ﬁrst epidemiologic study to investigate the relationship between mercury and thyroid autoantibodies. We report an association between blood mercury and thyroglobulin antibody positivity in US women.
Statistical adjustment for covariates did not substantially alter these relationships. Although we do not know the association between mercury and overt autoimmune disease among the women in this study, earlier research identiﬁed thyroglobulin antibody positivity as characteristic of other autoimmune diseases.
Given widespread exposure to low-levels of mercury in the general population, longitudinal research is merited to evaluate associations between biomarkers of mercury exposure and conditions associated with elevated thyroglobulin autoantibodies, such as systemic lupus erythematosus, ﬁbromyalgia, pernicious anemia, diabetes, rheumatoid arthritis, autoimmune thyroiditis, and thyroid cancer.
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Environment International covers all disciplines engaged in the field of environmental research. It seeks to quantify the impact of contaminants in the human environment, and to address human impacts on the natural environment itself. We recognize that scientific issues related to environmental health and human welfare are inherently interdisciplinary and, therefore, we welcome articles that cover the entire spectrum of sources, pathways, sinks and interactions between environmental pollutants, whether chemical, biological or physical. The primary criteria for publication are scientific quality and environmental significance.