New research shows that it may be safe for patients taking thyroxine replacement to have low but not suppressed thyroid stimulating hormone (TSH) levels. The research, presented at the Society for Endocrinology BES meeting in Manchester, shows for the first time that it may be safe for patients to take slightly higher doses of thyroxine than are currently recommended.
The thyroid gland produces hormones that regulate metabolism, in particular a hormone called thyroxine. Hypothyroidism occurs when the thyroid gland produces too little thyroxine. This condition affects approximately 3% of the UK population and is easily treated through taking daily doses of thyroxine hormone replacement. When treating hypothyroidism, clinicians aim to ensure that levels of another hormone called TSH also remains 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.
Dr Graham Leese, from Ninewells Hospital and Medical School, led a research team examining patients on thyroxine replacement therapy. They studied how variations in these patients' TSH levels affected their long-term health. The study followed 16,426 patients taking thyroxine (86% 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 (>4.0mU/l) or suppressed (≤0.03mU/l) TSH levels more frequently suffered from heart disease, abnormal heartbeat patterns and bone fractures compared to patients whose TSH levels are 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.