Thyroid medication has no effect on death rates in patients with subclinical hypothyroidism

Subclinical hypothyroidism is a mild form of underactive thyroid disease where patients have raised levels of thyroid stimulating hormone (TSH) but a normal concentration of free thyroid hormone. This condition is associated with certain risk factors for increased mortality such as high blood pressure and high cholesterol. There is some debate within the medical community on whether it is effective to treat these patients with a medication called levothyroxine, which increases thyroid hormone levels. Although this treatment is generally well-tolerated, a number of side-effects can occur if thyroid hormone levels are raised too much.

Researchers from Gentofte University Hospital in Denmark examined the medical records of 628,953 patients who had received thyroid function tests from 2000-2009. 12,212 (1.9%) patients were diagnosed with subclinical hypothyroidism. Of these, 2,483 patients (20.3%) were prescribed levothyroxine within the first six months. The remaining 9,729 patients (79.7%) either started levothyroxine therapy later than six months after their initial blood test, or did not receive any substitution treatment.

Patients were then followed for a mean time of five years. During follow up, 1,566 of the subclinical hypothyroidism patients died. There was no significant difference in mortality rates between patients who received levothyroxine treatment and those who did not.

Research Fellow, Mette Andersen, who led the study, said, "This is the largest population-based study to examine whether levothyroxine treatment for patients with subclinical hypothyroidism can affect their mortality. Using readily-available registry data, we were able to examine a large population and compare treated versus untreated subclinical hypothyroidism patients with respect to all-cause mortality."

"Our main finding was that levothyroxine treatment had no effect on overall death rates in subclinical hypothyroidism patients. Although previous studies have indicated that levothyroxine treatment may improve some markers of heart function, we found no evidence that this translates into increased survival for these patients."

"Any patients who are worried about their treatment should visit their doctor to discuss their concerns," concluded Andersen.

The team now plan to examine the effect of levothyroxine medication on a subset of subclinical hypothyroidism patients who also have heart conditions in more detail.