Objective

Since the positive role of thyrotropin (TSH) in bone remodeling has been recently emphasized, this cross-section study is aimed to evaluate the association of bone status with the level of TSH and free thyroxine (FT4) in the cohort of postmenopausal women after long-term treatment of thyroid disorders and age matched controls.

Methods

Urinary calcium (dUCa) and serum level of TSH, FT4 and of bone turnover markers (BTMs) such as alkaline phosphatase (ALP), osteocalcin (OC), cross linked N-telopeptide of type 1 collagen (NTx) as well as lumbar spine L 1-4 (BMD-L) and femoral hip (BMD-F) mineral density were determined in 113 postmenopausal women consisting of 42 patients with Graves disease treated by carbimazole, 32 patients with thyroid cancer treated with L-thyroxine and 39 age matched women without any thyroid and osteological disorders. For statistical evaluation t-test, Pearson's correlation coefficient and linear multiple regression were used.

Results

To compare the association of TSH versus FT4 with BMD and BTMs the pooled cohort of all 113 women was divided in two groups in terms of TSH level: 1. 34 women with low TSH (> or= 0.50 mU/l); 2. 79 women with normal TSH (0.51-4.3 mU/l). In spite of significantly higher FT4 level, the Group 2 with normal TSH level had significantly higher BMD-L and BMD-F (p< 0.001) and, in contrast, significantly lower urinary dUCa, ALP, OC (all at p< 0.001) and NTx (p< 0.01) as compared to the Group 1 with low TSH level. Linear multiple regression showed highly significant influence of TSH on BMD-L and BMD-F0 (p< 0.001) independent of age, FT4 and body mass index, while that of FT4 was not significant. The strength of linear interrelation between all variables used was finally tested by Pearson's correlation coefficient (Table 3) which was highly positive for TSH with BMD-F and BMD-L, but highly negative for TSH with serum NTx, OC, ALP) and urinary calcium (dUCa). In contrast, no significant correlation was found between the level of FT4 and BMD.

Conclusions

Irrespectively of FT4 level, postmenopausal women with normal TSH level showed a favorable bone status as compared to these with low level of TSH which is consistent with the view that TSH itself possibly participates in playing a favorable role in influencing the bone mineral density in adult women.