Thyroid hormones (THs) play a pivotal role in the regulation of metabolic activity
throughout all life stages. Cross-talk with other hormone systems permits THs to coordinate
metabolic changes as well as modifications in growth and maintenance in response to
changing environmental conditions. The scope of this review is to explain the relevant
basics of TH endocrinology, highlight pertinent topics that have been investigated
so far, and offer guidance on measuring THs in non-invasively collected matrices.