Linking hormones and weight

2013-08-05 00:00

THE thyroid is a butterfly-shaped gland that is situated in the front of the neck, just below the Adam’s apple. The thyroid’s role is to make thyroid hormones, which are secreted into the blood and carried to every tissue in the body. They regulate every aspect of metabolism, including heart rate and body temperature, as well as how much fat and carbohydrate fuel we burn.

The major thyroid hormone secreted by the thyroid gland is called T4 (or thyroxine). T4 is inactive and doesn’t have any effect in the body until it is activated by being converted to T3 (or triiodothyronine). The thyroid gland is stimulated to produce T4 by the presence of another hormone called thyroid-stimulating hormone (TSH). TSH is made in the pituitary gland. The pituitary gland regulates how much TSH it makes, depending on the level of T4 that it recognises in the blood.

The pituitary and thyroid glands work together closely, almost as a heater and its thermostat would. When the levels of T4 are low, the pituitary gland produces more TSH, which in turn stimulates the thyroid gland to produce more T4. As the T4 levels rise, TSH production slows down.

In order for thyroid hormones to perform all of their functions, they must circulate around the body and enter into the tissues. Some T4 is attached to transport proteins, preventing it from entering tissues, while the rest of the T4 travels unbound (free T4), allowing it to enter target tissues. When blood tests are done to test thyroid function, levels of TSH, T3, T4 and Free T4 can be measured to give a complete picture of how effectively the pituitary gland and thyroid gland are working.

Hyperthyroidism is a condition that occurs when the thyroid gland produces too much T4. Hyperthyroidism can accelerate the body’s metabolism significantly. This can cause sudden weight loss, a rapid or irregular heartbeat, sweating and nervousness or irritability. Hyperthyroidism can mimic many other health problems, which may make it difficult to diagnose.

Several treatment options are available for hyperthyroidism. Anti-thyroid medications and radioactive iodine are used to slow the production of thyroid hormones. Occasionally, surgery may be used to treat hyperthyroidism, where part or all of the thyroid gland is removed.

Although hyperthyroidism can be serious if ignored, most people respond well once it is diagnosed and treated.

At the opposite end of the scale, hypothyroidism (underactive thyroid) is a condition in which the thyroid gland doesn’t produce enough T4. The body’s processes start slowing down as the metabolism is not regulated correctly.

The body’s temperature drops, the skin gets drier and other symptoms such as fatigue and weight gain are common. Forgetfulness, constipation and depression may also be noted. These symptoms are so variable and non-specific that the diagnosis of hypothyroidism can sometimes be overlooked. Hypothyroidism cannot be cured, but can be very successfully controlled. Treatment focuses on replacing the amount of the hormone that the thyroid gland is not producing. T4 and TSH levels are routinely tested to ensure that the levels are returning to normal.

Although hypothyroidism most often affects middle-aged and older women, anyone can develop the condition, including infants and children.

The tiny thyroid gland, with its enormous influence on our health, is often blamed for unwanted weight gain. I have come across many patients battling to lose weight who have their thyroid tested in the hope that it offers some explanation for their struggle.

Next time, we will investigate whether there really is a link between thyroid function and weight.

• Sharon Hultzer is a consulting dietitian. She can be reached at

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