Bone Mineral Density and Bone Turnover Marker in a Subclinical Thyrotoxic State in Young Premenopausal Women

Subclinical thyrotoxicosis (SCH) is characterized by normal serum thyroid hormone levels and low thyrotropin levels. The impact of this condition on the skeletal system may vary depending on its cause, yet the relationship is not fully comprehended in premenopausal women. Studies are scarce about its effects on bone health in our population.

This study aims to evaluate the bone mineral density (BMD) and bone turnover markers in premenopausal women with SCH and determine if any differences exist based on the condition's etiology.

A cross-sectional study was conducted at Ramaiah Medical College involving 36 participants for one year and six months after approval from the Ethics Committee. The carboxy-terminal telopeptide of type I collagen in blood and BMD were measured at the lumbar vertebrae (L1-L4) and femoral neck by dual-energy x-ray absorptiometry (Hologic v 2.0, Hologic, Massachusetts, U.S.). Statistical analysis was done using IBM SPSS Statistics for Windows, Version 20 (Released 2011; IBM Corp., Armonk, New York, United States).  Results: The mean age of the study population was 35.2 ± 7.2 years. The etiology was Graves' disease [n=11 (33.3%)], iatrogenic [n=14(38.8%)], toxic adenoma [n=6 (15.1%)], and multi-nodular goiter [n=5 (15.1%)]. The mean BMI was 23.5 ± 3.8 kg/m², and the mean levels of corrected calcium, phosphorus, and 25 hydroxy-vitamin D were 9.12 ± 0.25 mg/dl, 2.95 ± 0.34 mg/dl, and 29.4 ± 6.4 ng/ml, respectively. The mean BMD at hip and spine was 0.81 ±0.16 g/cm² and 0.92±0.08 g/cm² respectively. The mean Z-score was (-0.02 ± 0.8) and (-0.92± 0.08) at the hip and spine. No significant difference was observed in the BMD at the hip (p = 0.14) or spine (p = 0.44) between the endogenous and exogenous subclinical thyrotoxic subgroups. At the same time, the carboxy-terminal telopeptide of type I collagen was significantly different between the two groups (p<0.05).

In our cross-sectional study of premenopausal women with SCH, BMD at the hip or spine as measured by dual-energy X-ray absorptiometry did not reveal any significant reduction. The subclinical thyrotoxic state may not have an adverse effect on bone health in premenopausal females with sufficient levels of serum 25-hydroxy-vitamin D in the short term.