The Association of Thyroid Function with Bone Density during Childhood.

Context: Although the skeleton is a well-known thyroid hormone target organ, very little data are available on the association of thyroid function with bone outcomes during childhood. Objective: To study the association of thyroid function with bone mass during childhood. Design, Setting, and Participants: Population-based prospective cohort including 4204 children with TSH and free T4 (FT4) measured at the age of 6 years. Main Outcome Measures: Bone density was assessed by a total body dual-energy X-ray absorptiometry scan at the median age of 6 years (95% range, 5.6 to 7.9) and at the age of 10 years (95% range, 9.0 to 10.9) in 4204 and 3404 participants, respectively. Results: There was an inverse association of TSH with bone mineral density (BMD) at the age of 6 (beta -0.028 +/- 0.011, P = 0.009) and with follow-up measurements at the age of 10 (beta -0.027 +/- 0.011, P = 0.014), but not with bone mineral content (BMC) at the age of 6 (beta -0.028 +/- 0.015, P = 0.06) or for follow-up measurements of BMC at the age of 10 (beta 0.011 +/- 0.015, P = 0.47). There was an inverse association of FT4 with BMD (beta -0.016 +/- 6 0.006, P = 0.014) and BMC (beta -0.023 +/- 0.009, P = 0.009) cross-sectionally, and also at the age of 10 years (BMD: beta -0.018 +/- 0.007, P = 0.007; BMC: beta -0.021 +/- 0.009, P = 0.020). Conclusion: A higher FT4 concentration is associated with lower bone mass at the age of 6 and at the age of 10 years. These data provide insights into the effects of thyroid function on bone physiology during childhood.