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Endocrinology Other
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my personal edition > endocrinology other > news
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DGReview
Effects of Levothyroxine on Bone Mineral Density Remain Unclear
A DGReview of :"The effect of levothyroxine therapy on bone mineral density: a systematic review of the literature"
Experimental and Clinical Endocrinology and Diabetes
03/03/2004
By Deanna M Green, PhD
Current data regarding the effects of levothyroxine on bone mineral density (BMD) are conflicting due to the heterogeneity of available studies, according to the authors of a systematic review.
Levothyroxine is typically prescribed as replacement to thyroid-stimulating hormone (TSH) or to suppress TSH in patients with thyroid disease. A number of mainly narrative studies have assessed the impact of endogenous or exogenous thyroid hormone on BMD levels. However, the results have not been conclusive. This lack of a definitive understanding has resulted in continuing debate over the safety levothyroxine.
Dr. Rita Schneider and colleagues, Nuclear Medicine Clinic, University of Wurzburg, Wurzburg, Germany, conducted a literature review on the effects of levothyroxine therapy on BMD.
They identified 63 primarily observational studies that measured BMD in 2,914 patients who were treated with levothyroxine as TSH-suppressive and/or replacement therapy and 365 control patients. Most subjects were women, and postmenopausal women were evaluated twice as often as premenopausal women.
The mean levothyroxine dose used in most studies was 148 mcg/day. Mean duration of treatment ranged from 6 months to 20 years, and follow up ranged from 12 to 72 months.
"Current findings are complex and confusing, therefore the evaluation and interpretation of the large range of study effects only allowed a qualitative review of the literature," the authors highlight.
Overall, 31 studies found that levothyroxine had no effects on BMD and 32 found at least a partial effect. Nine studies showed that levothyroxine had an overall adverse effect of on BMD.
Most studies showed that longer duration of treatment and higher levothyroxine doses did not result in reduced BMD levels, while TSH levels did not appear to correlate with BMD.
Some studies reported a tendency towards site-specific loss of BMD, regardless of the dose used. Notably, cortical bone loss was mainly seen at peripheral sites.
As seen in the general population, a number of studies reported a negative correlation between age and BMD. In this group of studies, there was no significant effect of levothyroxine on BMD in men and the effect seemed greater in postmenopausal women than in premenopausal women.
However, the effects of levothyroxine remain unclear, the authors write. It also remains unclear whether underlying thyroid diseases are independent or additional risk factors for reduced BMD.
The authors write that studies conducted to date are not well designed "and too disparate to confirm or exclude the effectiveness of levothyroxine on bone mineral density beyond any doubt, therefore conclusions are preliminary."
They add that the studies were substantially heterogeneous and were limited by their moderate quality, small size and inadequate control for confounders such as age.
Exp Clin Endocrinol Diabetes 2003 Dec;111:8:455-70.
"The effect of levothyroxine therapy on bone mineral density: a systematic review of the literature"
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