A study of thyroid function in the pre- and post-menopause.
Serum levels of thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free triidotthyronine (FT3), free thyroxine (FT4) and thyroxine-binding globulin (TBG) were measured in 382 healthy women who were attending a menopause clinic. Of these women, 140 were in the pre-menopausal phase, 162 had been post-menopausal for less than 3 yr and 60 had been post-menopausal for greater than 3 yr. Analysis of the results as a function of climacteric situation, revealed that the only significant difference was a lower serum concentration of FT3 in the women who had been post-menopausal for over 3 yr than in the women who were in the pre-menopausal phase. Statistical analysis of the results as a function of both climacteric situation and age showed that the serum level of TBG increases with age, while serum levels of circulating thyroid hormones decrease, and that although the menopause does not bring about marked changes in thyroid function, it nevertheless tends to reduce that function, especially when menopause occurs at the expected time. Finally, by correlating values with T4 values on an individual basis, it was possible to ascertain that when physiological changes in thyroid function do occur in the climacteric, they are not caused by primary changes in TSH secretion.