Decreased BMD Associated With Hypothyroidism Among Women

Women with hypothyroidism have lower bone mineral density (BMD) even after euthyroidism had been reestablished. These findings, from a cross-sectional control study, were published in Endocrinology.

Women aged mean 47 plus or minus 12 years were recruited for this study at the Odense University Hospital in Denmark between 2011 and 2016. Women with Hashimoto thyroiditis (n=32) were matched with healthy controls (n=32) for sex, age, and menopausal status. At baseline and 1 year after euthyroidism was restored, women with hypothyroidism and controls had their distal radius and tibia assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT), and their spine and hip assessed by dual-energy X-ray absorptiometry (DXA). BMD was measured by a finite element analysis.

At baseline, patients with hypothyroidism had median thyroid stimulating hormone levels of 3.78 mIU/L (interquartile range [IQR], 2.12-5.78), free T3 of 4.81 pmol/L (IQR, 4.08-5.09), free T4 of 16.9 pmol/L (IQR, 15.2-19.2), and 25-hydroxyvitamin D of 65.3 (47.6-98.7).

At baseline, compared with controls, women with hypothyroidism had higher radius total and trabecular (mean, 14.6%±29.3% and 19.8%±37.1%: P =.04 for both) bone areas and lower cortical volumetric BMD (mean, -2.2%±6.5%; P =.032).

After euthyroidism had been reestablished for a minimum of 12 months, 1 patient was lost to follow-up, 1 was excluded after donating a kidney, 1 was at full-term pregnancy, 1 was excluded after losing 48% of her body weight following gastric bypass surgery, and 1 was diagnosed with an eating disorder. The remaining 27 participants had median thyroid stimulating hormone levels of 2.14 mIU/L (IQR, 0.58-4.32), free T3 of 4.21 pmol/L (IQR, 3.78-4.84), free T4 of 18.8 pmol/L (IQR, 17.1-22.1), and 25-hydroxyvitamin D of 67.9 nmol/L (IQR, 61.6-96.8).

Also among women with reestablished euthyroidism, trabecular area in the tibia increased significantly (0.2%;±0.6%; P =.047). Cortical porosity also increased (8.2%±11.5%; P <.01), while total and cortical volumetric BMD decreased (-1.1%±1.9%; P =.01 and -0.8%±1.4%; P <.01). In the radius, cortical porosity increased (18.9%±32.7%; P =.02) while trabecular and cortical (-1.5%±4.6%; P =.02 and -0.9%±1.8%; P =.02) volumetric BMD and trabecular bone volume per tissue volume decreased (-1.6%±4.6%; P <.01).

Compared with controls, after euthyroidism was maintained for 1 year, total spinal area BMD decreased significantly (-1.3%±3.0%; P =.04).

The limitations of this study were that only women were included and most participants (23 out of 32) had mild hypothyroidism. Therefore, it remains unclear whether the observed patterns in bone health are more apparent among patients with severe hypothyroidism.

“Hypothyroidism was associated with an increased trabecular bone area and a lower mineral density of cortical bone in the radius,” the researchers concluded. “Restoration of euthyroidism mainly increased cortical porosity, while estimated bone strength was unaffected.”

“Future studies…are needed to further qualify the influence of hypothyroidism and its treatment on bone microarchitecture,” they added.

Reference

Obling M L, Nicolaisen P, Brix T H, et al. Restoration of euthyroidism in women with Hashimoto’s thyroiditis changes bone microarchitecture but not estimated bone strength. Published online July 4, 2020. Endocrine. doi: 10.1007/s12020-020-02398-y