Adults with thyroid cancer taking less than 115 µg per day or at least 145 µg per day of levothyroxine after thyroidectomy or radioiodine ablation therapy had an increased risk for fractures compared with those taking 115 to 144 µg per day, according to study findings.
Park, MD, MPH, of the department of family medicine at the National Health Insurance Service Ilsan Hospital in Korea, and colleagues evaluated data from the Korean National Health Insurance database on 185,956 adults with thyroid cancer and matched comparison subjects (controls) to determine fracture incidence among them and associations between levothyroxine use and fracture risk. Participants had a mean age of 46.8 years and 82.8% were women. Follow-up was a mean of 3.96 years.
Participants with thyroid cancer were divided into groups based on levothyroxine dosage quartiles: first (< 115 µg per day), second (115-144 µg per day), third (145-169 µg per day) and fourth ( 170 µg per day).
Over follow-up, 0.56% of the thyroid cancer group and 0.58% of the control group experienced a fracture. The risk for osteoporotic fracture overall was not elevated in the thyroid cancer group compared with controls. Participants receiving the highest dose of levothyroxine had a higher risk for fracture compared with the other doses (HR = 1.25; 95% CI, 1.07-1.45), and those receiving the second quartile dose had a lower risk (HR = 0.71; 95% CI, 0.59-0.84).
When the second quartile dose was used as reference, the risk for fracture was increased in those in the first quartile (adjusted HR = 1.31; 95% CI, 1.08-1.59), third quartile (adjusted HR = 1.5; 95% CI, 1.26-1.79) and fourth quartile (adjusted HR = 1.79; 95% CI, 1.51-2.13).
“Our study shows that both high and low dosages of levothyroxine treatment [are] associated with a higher risk of fractures in a J-shaped dose-dependent manner in post-thyroidectomy patients,” the researchers wrote. “Future studies are needed to determine how to optimize TSH suppression and how to screen and manage fracture risk.” – by Amber Cox
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