TG and Obesity: Interestingly, the latter study also unveiled a negative relationship between selenium and free thyroxine (T4) and 3-3’-5-triiodo-L-thyronine (T3), both thyroid hormones regulating energy metabolism and controlled by the hypothalamic-pituitary-thyroid axis; however, the observed increases in thyroid hormone in women with obesity were not sufficient to indicate compromised thyroid function.