Study designs of evaluations included in the review
There were no specified inclusion criteria for the study design. Cross-sectional studies, cohort studies and intervention trials were included in the review.
Specific interventions included in the review
Studies of levothyroxine therapy of any dose or duration were eligible for inclusion. In the included studies, the treatment dosage ranged from 72 to 259 microg/day and the mean duration of treatment ranged from 0.5 to 20.4 years.
Participants included in the review
There were no inclusion criteria for the participants. The participants were aged from 9 to 98 years, although the majority of included studies were of adults and included women only. There were twice as many studies of postmenopausal than premenopausal women. Four studies included only men. Most of the studies included patients with homogeneous diagnoses although some studies did combine different thyroid diseases.
Outcomes assessed in the review
The studies were required to report BMD as an outcome. BMD could be assessed by any method and measured at any site. Dual-energy X-ray absorptiometry was the most commonly used technique, although single- and dual-photon absorptiometry, quantitative computed tomography, peripheral quantitative computed tomography and quantitative ultrasound were also used. The number of measured sites ranged from 1 to 10. The sites included lumbar spine and peripheral (ultradistal radius, calcaneus) trabecular bone, central (total body, trunk, pelvis) and peripheral (proximal radius, mid radius) cortical bone, and central (Ward's triangle, trochanter, total hip) and peripheral (distal radius) mixed cortical and trabecular bone.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.