There are clinical similarities between anorexia nervosa and hypothyroidism. Circulating levels of T₄ and particularly T₃ have been reported to be low in this eating disorder. Previous reports have, however, shown normal basal levels of serum TSH with normal or delayed responses to TRH. To assess thyroid function and the hypothalamic-pituitary axis in 21 women with anorexia nervosa, serum levels of free and total thyroid hormones, binding proteins, and TSH employing an extremely sensitive assay (detection limit = 0.02 µU/ml) were measured. Serum T₄, free T₄, T₃, free T₃, TSH, TBG and TBPA concentrations were significantly lower and rT₃ levels were significantly higher in anorexia nervosa patients than in normal controls. A delayed TSH response to TRH was noted in 66 % of patients, hyporesponsiveness was seen in another 24 %, and a normal response in only 10%. In 10 anorexia nervosa patients studied after weight gain, T₄, T₃, free T₃, TSH, TBG and TBPA were significantly increased, and rT₃ was significantly decreased. No change in mean free T₄ levels with weight gain was noted. Other parameters of hypothalamic dysfunction in anorexia nervosa have been reported and the present data suggest that apparent hypothalamic hypothyroidism occurs perhaps as an adaptation to prolonged starvation.
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Tamai et al. (2010) studied this question.