These results show for the first time that it may be safe for patients taking long-term thyroxine replacement therapy to have a low but not suppressed TSH level.  These patients do not show an increased risk of suffering from heart disease, bone fractures or abnormal heartbeat patterns.  This means that patients may be able to take slightly higher doses of thyroxine than are currently recommended without having an adverse effect on their health.

Researcher Dr Graham Leese, a Consultant at NHS Tayside and Honorary Reader in Diabetes and Endocrinology at the University of Dundee, said:

"This is the first population-based study to show that having slightly lower TSH levels when taking thyroxine replacement is not detrimental to health. We found that having high or suppressed levels of TSH did lead to a higher risk of heart disease and bone fractures and so it is important that we continue to monitor TSH levels carefully to ensure that neither of these situations happen.

 "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. Our findings mean that it may be safe for patients with hypothyroidism to take marginally higher doses of thyroxine than are currently recommended.  However careful monitoring of these patients would still required.  We now need other studies to confirm our findings before any changes are made to routine clinical care."

Source: Society for Endocrinology