Seniors – Have Your Thyroxine Dosage Checked Regularly

Levothyroxine is a synthetic form of thyroxine – a thyroid hormone – that is widely taken to treat an underactive thyroid gland, or hypothyroidism as it is called.  Over 20% of older people take levothyroxine replacement long-term;  most of them are women.  If the dosage is too high, an underactive gland becomes overactive (hyperthyroidism), which may increase the risk of fractures.  A Canadian study has explored the effects of levothyroxine dosage on the risk of fractures in people over 70, and its findings have been reported in the British Medical Journal.   

The researchers used Ontario's prescription-benefit database for their study of Ontario's prescription-benefit database more than 210,000 adults (average age 82) who were using thyroxine any time over a 5-year period.  Fracture data were collected over the time of the study and set in relation to levothyroxine use (current, recent past, or remote) and dosage (high, medium, or low cumulative dose).

Ten percent of the study population experienced at least one fracture during the study; 88% of them were women.  Current and recent levothyroxine use (i.e. within the past 6 months) were both associated with an increased risk for fracture, compared with remote use.  Among current users, both high and medium dosage (over 0.093 mg/day and 0.044 to 0.093 mg/day, respectively) carried an increased fracture risk over that for low dosage subjects (below 0.044 mg/day).

The researchers conclude that this study provides evidence that levothyroxine treatment may double or triple the risk of fractures in older people. They suggest that closer monitoring of such patients is warranted.  Unfortunately, thyroid function monitoring data were not available to the researchers.  Ideally, thyroid stimulating hormone (TSH) levels should be determined before starting treatment, and then at regular intervals.  An expert writing in an editorial states: “Elderly people need relatively low thyroxine doses, so serum TSH should be regularly monitored and a suppressed TSH should be avoided in such patients."  Normal adult serum TSH values are 0.4-4.5 mU/L;  fractures have been reported with levels below 0.03 mU/L.