CD4 and hyperthyroidism: However, although animal studies suggest a link between PBDEs and hypothyroidism, PBDE exposure is associated with subclinical hyperthyroidism in this population (Chevrier J, Harley KG, Bradman A, Gharbi M, Sjodin A, Eskenazi B, unpublished observations) and with increased T4 or decreased thyroid-stimulating hormone in other epidemiologic studies (Hagmar et al. 2001; Meeker et al. 2009; Turyk et al. 2008).