Prevention of thyroxine-induced bone loss in postmenopausal women-the effect of calcium supplementation and intranasal calcitonin

Abstract

Although controversies exist on the possible adverse effect of thyroxine (T4) on bone mass, most studies reported bone loss in estrogen deprived-postmenopausal women taking suppressive doses of T4. We prospectively studied 46 postmenopausal women with carcinoma of thyroid for two years to evaluate the rate of bone loss and to assess whether calcium supplementation or calcitonin was able to decrease the rate of bone loss. All patients were receiving a stable dose of L-T4 (170+60 pg) for more than one year and had TSH levels of <0.03 mIU/L. The calcium intake was low and averaged 545 + 129 g/day as assessed by dietary recall. The subjects were randomised into 3 groups: (1) intranasal calcitonin 200 pg daily for 5 days per week plus 1000 mg calcium daily (Calcium Sandoz Forte), (2) calcium alone or (3) placebo. Total body and regional bone mineral density (BMD) were measured by a durai energy X-ray absorptiometry bone densitometer (Norland XR-26) at 6-monthly interval. The results showed that both group 1 and 2 did not have bone loss while patients in group 3 showed significant bone loss at the end of two years (Lumbar spine 5.0%, hip 6.7%, trochanter 4.7%, Ward triangle 8.8%). There were no differences between group 1 and 2. At 1 year, patients in group 3 already had significantly higher osteocalcin levels compared with those in group 1 and 2. No significant changes were detected in the bone specific alkaline phosphatase levels as well as the urinary hydroxyproline levels. PTH level decreased at 6 months in group 1 but returned to basal state at 12 months onwards. In conclusion, T4 suppressive therapy was associated with bone loss in postmenopausal women which could be prevented by either calcium supplementation or intranasal calcitonin, although the latter did not provide additional benefit when compared to calcium alone.