New research shows that it may be safe for patients taking thyroxine replacement to have low but not suppressed thyroid stimulating hormone (TSH) levels and for them to take slightly higher doses of thyroxine than are currently recommended.

     The thyroid glad produces hormones that regulate metabolism, in particular a hormone called thyroxine.  Hypothyroidism occurs when the thyroid gland produces too little thyroxine.  The condition is easily treated through taking daily doses of thyroxine hormone replacement.  When treating hypothyroidism, clinicians aim to ensure that levels of TSH also remain in the normal range.  TSH stimulates the thyroid gland to release thyroxine.  Its levels are controlled by thyroxine in a negative feedback loop, with greater levels of thyroxine leading to a decreased TSH production.  There have been concerns that abnormal TSH levels can be bad for health and lead to a greater risk of a number of conditions, such as heart disease and osteoporosis.

     A research team led by Dr. Graham Leese, of the University of Dundee, Tayside, UK, conducted a study following 16,426 patients taking thyroxine (86 percent female, mean age 60 years) and examined how their risk of contracting a range of diseases varied with their TSH levels.  The study found that patients with very high or suppressed TSH levels more frequently suffered from heart disease, abnormal heartbeat patterns, and bone fractures compare to patients whose TSH levels were in the normal range (0.4-4.0 mU/l).  Patients who had a slightly low TSH level (0.04-0.4mU/l) did not have an increased risk of contracting any of these conditions.

     Dr. Leese reports, "Prescribing thyroid hormone replacement therapy is a careful balancing act as doctors need to ensure that the levels of a number of hormones all remain with the normal range after treatment."  He also says that while it may be safe for patients with hypothyroidism to take marginally higher doses of thyroxine than are currently recommended, careful monitoring of these patients would still be required.

     Dr. Leese adds, "We now need other studies to confirm our findings before any changes are made to routine clinical care."

     These research results were presented on March 16, 2010, at the Society for Endocrinology BES conference held in Manchester, UK.

--Source: Society for Endocrinology, March 16, 2010