Does thyroid hormone replacement therapy affect bone density? — Donna M. O’Brien, ANP, North Truro, Mass.

Before the advent of anti-thyroid hormone drugs in the 1940s, osteoporosis from hyperthyroidism was very common and potentially severe. Since then, adverse bone changes from over-replacement of thyroid hormone are more the norm.

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Thyroid hormone excess mostly increases bone resorption from osteoblasts that are not accompanied by increases in bone formation. This effect is more pronounced in postmenopausal women. Clinically, this means that patients with suppressed thyroid-stimulating hormone (TSH) (below normal range) on thyroid hormone therapy are at higher risk for bone loss.

Patients on thyroid hormone after thyroidectomy for thyroid cancer typically maintain a suppressed TSH level to inhibit any recurrence of thyroid cancer; these patients should be monitored more closely for osteoporosis. Likewise, it is important to avoid a suppressed TSH in other individuals on thyroid hormone replacement to avoid this adverse event (Clin Endocrinol [Oxf]. 2004;61:285-298). — Kathy Pereira, DNP, RN, FNP-BC, ADM-BC, assistant professor, coordinator, Family Nurse Practitioner Program, Duke University School of Nursing, Durham, N.C. (168-3)

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