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Effect of Thyroxine on Blood Pressure

Tess Thompson

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Thyroxine (T4) is one of the two main hormones secreted by the endocrine gland, thyroid, which is located in front of your neck. The other two thyroid hormones are triiodthyronine (T3) and calcitonin. While T4 and T3 regulate the body’s metabolism, calcitonin tends to lower calcium levels in the blood plasma and restricts resorption of bone.

For proper bodily functioning, it is important that the level of thyroid hormones remains within the normal range. Hypothyroidism is one of the two common thyroid problems. The condition refers to low thyroid or an inadequate production of hormones. Symptoms of hypothyroidism tend to vary, and most of the symptoms mimic signs associated with the normal aging process. Since the thyroid hormones stimulate metabolism, hypothyroidism usually manifests as lethargy, general fatigue, unexplained weight gain and intolerance to cold. This can sometimes be accompanied by skin problems like dry skin, coarse hair, brittle nails and ocular problems like swelling around the eyes, as well as problems with the reproductive, gastrointestinal and cardiovascular systems.

Hypertension or high blood pressure is one of the less talked about cardiovascular symptoms of hypothyroidism. Studies have been conducted on patients receiving hypothyroid treatment with thyroxine replacement therapy. The results show a remarkable affect of thyroxine on blood pressure on hypertensive people. Gradual induction of thyroid supplements or exogenous hormones was seen to lead to a reduction in blood pressure and the heart rate of both hypertensive and normotensive patients. The obvious conclusion is that treatment of hypothyroidism with exogenous thyroid hormones can reverse hypertension in people suffering from hypothyroidism.

Hypertension resulting from hypothyroidism is a relatively less common disorder and is seen in only about 1% of referred cases. Before considering hypothyroidism as a cause of hypertension, it is important to be sure whether the problem of low thyroid exists or not.

Thyroid dysfunction is one of the more difficult disorders to diagnose. Thyroid functioning is usually diagnosed using thyroid function blood tests to determine blood levels of T3 and T4 and the thyroid stimulating hormone (TSH), secreted by the pituitary gland in the brain. The findings of laboratory tests showing classical symptoms of thyroid problems often tell an entirely different story. Recent studies also show that mutations in transporters that carry thyroid hormones across cells can cause resistance to thyroid hormones. Such resistance often leads to various thyroid conditions without showing abnormal levels of thyroid hormones.