Researchers have shown that subclinical hyperthyroidism is associated with higher risks of bone fractures, publishing the results of their study in the journal JAMA.
Subclinical hyperthyroidism occurs when the body has a low concentration of thyroid-stimulating hormone in an individual without clinical systems and produces normal results in blood tests for concentrations of the thyroid hormone. This overt type of hyperthyroidism is a known risk factor for fractures and osteoporosis, although exact associations are unclear.
Led by Nicolas Rodondi, M.D., M.A.S., from the Bern University Hospital in Switzerland, the researchers analyzed data from over 70,000 subjects across 13 studies, assessing the connection between fractures and subclinical thyroid dysfunction. Information used by the researchers were gathered from prospective cohorts in Japan, Australia, Europe and the United States. In these studies, thyroid function was defined as subclinical hypothyroidism with normal thyroxine, subclinical hyperthyroidism and euthyroidism.
Out of the 70,298 subjects included in the study, 5.8 percent were categorized as having subclinical hypothyroidism, while 3.2 percent had subclinical hyperthyroidism. The researchers found that those with subclinical hyperthyroidism had higher risks for bone fractures of all kinds. Those with the highest risk, however, are those with suppressed thyroid-stimulating hormones and those with endogenous subclinical hyperthyroidism. The researchers didn't find associations between fractures and subclinical hypothyroidism.
"Our pooled data analysis demonstrates that subclinical hyperthyroidism was associated with increased fracture risk and provides insight on defined subgroups," said the researchers.
Current guidelines in place recommend treatment for subclinical hyperthyroidism if thyroid-stimulating hormone levels are consistently lower than or at least 0.1 mIU/L in people at least 65 years old. However, while the association between increased risks of bone fractures and subclinical hyperthyroidism has been made, it has not been determined how treating the condition will be able to help prevent fractures. The researchers recognize this potential area of study and suggest further work is needed to clarify the effects of treatment on bone fracture risk.
Researchers from the University of California, San Francisco, University Hospital of Lausanne, University of Minnesota, VA Medical Center, University of Pennsylvania, Florida International University, Erasmus Medical Center, the Norwegian University of Science and Technology, the Trondheim University Hospital, the Leiden University Medical Center, the University of Cambridge, Radiation Effects Research Foundation, University of Western Australia, Imperial College London, University of Sheffield, University College Cork, University of Pittsburgh, University of Washington, Nord-Trøndelag Hospital Trust, University Hospital of Parma, University of Glasgow, University of Copenhagen, National Institutes of Health, and the Sir Charles Gairdner Hospital also contributed to the study.
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