Thyroid Function and Postmenopause

There is an increasing prevalence of high levels of thyroid stimulating hormone (TSH) with age - particularly in postmenopausal women - which are higher than in men. The incidence of thyroid disease in a population of postmenopausal women is as follows: clinical thyroid disease, about 2.4%; subclinical thyroid disease, about 23.2%. Among the group with subclinical thyroid disease, 73.8% are hypothyroid and 26.2% are hyperthyroid. The rate of thyroid cancer increases with age. The symptoms of thyroid disease can be similar to postmenopausal complaints and are clinically difficult to differentiate. There can also be an absence of clinical symptoms. It is of importance that even mild thyroid failure can have a number of clinical effects such as depression, memory loss, cognitive impairment and a variety of neuromuscular complaints. Myocardial function has been found to be subtly impaired. There is also an increased cardiovascular risk, caused by increased serum total cholesterol and low-density lipoprotein cholesterol as well as reduced levels of high-density lipoprotein. These adverse effects can be improved or corrected by L-thyroxine replacement therapy. Such treatment has been found to be cost-effective. With time, overt hypothyroidism can develop. Therefore, routine screening of thyroid function in the climacteric period to determine subclinical thyroid disease is recommended. Hormone replacement therapy (HRT) in women with hypothyroidism treated with thyroxine causes changes in free thyroxine and TSH. Increased binding of thyroxine to elevated thyroxine-binding globulin causes an elevation of TSH by feedback. Since adaptation is insufficient, there is an increased need for thyroxine in these women taking HRT. TSH levels should be controlled at 12 weeks after the beginning of therapy. At higher age the need for iodine and thyroxine is decreased. Therefore, therapy has to be controlled. For bone metabolism thyroid hormones play a dominant role. While there are only marginal differences between hypothyroid patients and euthyroid controls, there are large differences for hyperthyroid patients. Previous thyrotoxicosis and subsequent long-lasting L-thyroxine treatment are together associated with reduction in femoral and vertebral bone density in postmenopausal women. In these cases HRT is important for the control of bone loss.