Thyroid Function and Obesity

Abstract

Important interaction exists between thyroid function, weight control, and obesity. Several mechanisms seem to be involved, and in studies of groups of people the pattern of thyroid function tests depends on the balance of obesity and underlying thyroid disease in the cohort studied. Obese people with a normal thyroid gland tend to have activation of the hypothalamic-pituitary-thyroid axis with higher serum TSH and thyroid hormones in serum. On the other hand, small differences in thyroid function are associated with up to 5 kg difference in body weight. The weight loss after therapy of overt hypothyroidism is caused by excretion of water bound in tissues (myxoedema). Many patients treated for hyperthyroidism experience a gain of more weight than they lost during the active phase of the disease. The mechanism for this excessive weight gain has not been fully elucidated. New studies on the relation between L-T₃ therapy and weight control are discussed. The interaction between weight control and therapy of thyroid disease is important to many patients and it should be studied in more detail.

MECHANISMS IN ENDOCRINOLOGY: The crosstalk between thyroid gland and adipose tissue: signal integration in health and disease

“…Besides its influence on thermogenesis, T 3 might also influence REE by regulating the spontaneous motor activity. Indeed, shortly after the injection of T 3 into the pre-optic region of hypothyroid rats, an increase in motor activity is observed (16).…”

“…Body weight regulation is achieved through a finetuning between energy intake and energy consumption, the latter being determined by resting energy expenditure (REE), non-exercise activity, and voluntary physical activity. In homeothermic species, such as humans, T 3 has acquired a critical role in temperature homeostasis and is responsible for w30% of REE (11). The T 3 -induced thermogenic activity is exerted through the thyroid hormone receptor a (TRa) (12,13), while TRb is a key regulator of cholesterol metabolism (14).…”

“…Alongside a chance association, a direct relationship between 'thyroid and obesity' has been hypothesized (1,2,3,4,5). Thyroid hormone is indeed an important determinant of energy expenditure and contributes to appetite regulation.…”

Changes in Hepatic TRβ Protein Expression, Lipogenic Gene Expression, and Long-Chain Acylcarnitine Levels During Chronic Hyperthyroidism and Triiodothyronine Withdrawal in a Mouse Model

“…There also was a trend toward increased triglyceride concentration, consistent with the lipogenic pathway being activated functionally. Interestingly, a significant proportion of patients experience weight gain after successful therapy for hyperthyroidism (33). Although the precise mechanism(s) for this observation is not known, it has been suggested that a delayed adaptation of appetite and food intake in combination with the decreased energy expenditure after returning to euthyroidism may be contributory (34).…”

Gender differences in thyroid function and obesity among finnish women and men. The FIN-D2D-study

“…The association between obesity and thyroid function is complex, because overeating with accumulation of fat and the development of obesity seems to activate the hypothalamic-pituitary-thyroid axis, leading to changes in thyroid function tests, which overlap with abnormalities seen in primary thyroid disease [5].…”