Obesity and thyroid function

A reciprocal interaction between the hypothalamo-pituitary-thyroid axis and the adipose tissue is required for the proper homeostasis of energy balance. In this chapter, the mechanisms by which the two systems regulate each other and the effects of thyroid dysfunctions on body weight will be discussed. In both lean and obese subjects, thyroid hormone and TSH levels are strongly influenced by the individual nutritional status. Furthermore, obesity can be associated with variations of circulating thyroid hormone and TSH. Whether obesity is a risk factor for thyroid diseases (autoimmunity, nodularity, cancer) remains a matter of debated investigation. While the hormonal substitutive treatment is required when obesity is associated with subclinical or overt hypothyroidism, we do not recommend thyroid hormone treatment in case of the isolated hyper-thyrotropinemia often detected in obese patients. Historically, many attempts have been carried out to treat obese euthyroid subjects by administration of thyroid hormones, their analogues, or derivatives, with the aim of increasing energy expenditure and promoting weight loss, but at present such type of intervention is not advisable outside very well-controlled clinical trials.