TG and hyperthyroidism: Although all thyroid hormone values remained within reference ranges, the significant increases in T4, fT4, T3 and fT3 at the supranutritional iodine intake, particularly in rats receiving iodoquinoline-biofortified lettuce, together with unchanged TSH, indicate a modest up-regulation of thyroid hormone production and/or peripheral T4-to-T3 conversion rather than overt hyperthyroidism.