What does the thyroid do?

Consider the thyroid's role like the cruise control unit for the body. Cruise control keeps the car running at a constant steady speed. When we do not want to worry about having to keep a steady foot on the accelerator, we turn on cruise control and the car maintains a normal speed without any effort.

Thyroid hormone keeps the rest of the body working at the right speed. If thyroid hormone levels decrease, cells throughout the rest of the body decrease in activity. As a result, the cells use less energy and more energy is available to be stored and the weight increases, even though the appetite decreases. Less heat is produced, the person becomes cold and the sweat glands do not keep the skin moist anymore. The brain just wants to sleep all the time. The heart beats slower, the bowels become sluggish, everything slows down.

Why can’t I lose weight and why am I always tired?

Mrs Wallis is a 32 year old primary school teacher. During the past few years, she’s been noticing that she hasn’t the energy to get through the day any more, and that she’s always tired. She remembered that her mother had a problem with her thyroid and only recently her sister who was also feeling fatigued, was diagnosed with hypothyroidism. She commented that she now feels much better since changing her diet.

Mr Thompson is a 40 year old journalist, and has always had trouble with his weight. He has always dieted and exercised regularly until a few years ago when he started to lose weight even though he was eating a lot more. Following a visit to his doctor, he was found to have an over active thyroid and was given a drink of radioactive iodine for treatment. Three months later, his weight came back on, his muscles were cramping, he was always cold and his face was puffy. Back to the doctor, who diagnosed an under active thyroid, also known as hypothyroidism. Following this diagnosis, Mr Thompson was started on some medication, but his weight kept on increasing. He found that, in order to keep his weight from gaining, he had to eat less than before but exercise more.

Our two examples above of the fictitious Mrs Wallis and Mr Thompson are typical of many clients that have problems with weight loss due to thyroid activity. The most common symptoms are tiredness and weight gain. Let’s look in more detail the thyroid’s role and the test used to check it’s functionality.

Setting the Cruise Control - The Pituitary.

The pituitary gland is known as the master gland. It is located at the base of the brain between the temples. It sets the function level of our thyroid gland and therefore the thyroid hormone level in the blood stream.

As soon as the levels of thyroid hormone in the body decrease, the pituitary gland puts out more Thyroid Stimulating Hormone (TSH) which goes through the blood stream and then stimulates the thyroid gland to produce, then release more thyroid hormone. If, for some reason, the thyroid hormone levels increase in the body, the pituitary gland stops secreting TSH, therefore the thyroid is not getting signals to manufacture, and then secrete thyroid hormone into the blood stream.

Thyroxine (T4) is the main hormone produced by the thyroid gland, but T4 is inactive and has to be converted into triiodothyronine (T3). This process happens throughout the entire body. The pituitary gland monitors the levels of T3 and if they are too high, the pituitary stops secreting TSH. This causes the thyroid to stop working causing the thyroid levels to return to a normal level. The pituitary gland secretes more TSH if the T3 levels are too low, which makes the thyroid start releasing thyroid hormone again bringing the levels back up to normal.

Measuring the settings for Cruise Control – TSH.

Abnormal thyroid function occurs within the thyroid itself and not the pituitary. There are times when the thyroid can be stimulated by antibodies (Graves' disease) produced by immune cells within the thyroid. As a result, this causes lower TSH levels. At other times, antibodies may destroy or block the thyroid (Hashimoto's Thyroiditis) and elevate the TSH levels. The most sensitive indicator of changes in thyroid function is the level of TSH in the blood.

There are now reliable new assays for measuring very low levels of TSH. The main screening test for a dysfunctioning thyroid is the measurement of TSH. The TSH level is quickly decreased with even the slightest increase in thyroid hormone levels (mainly T3). A slight decrease quickly elevates the level of TSH. Changes in pituitary function to cause changes in thyroid function happen very occasionally.

Decreased TSH, thyroid levels and thyroid stimulation is caused by an under active pituitary gland. If there is a tumour on the pituitary gland that secretes, and therefore increases TSH levels, this can increase the thyroid stimulation and increase thyroid levels. If there is a pituitary problem and the TSH is measured, this could give rise to a misleading diagnosis. This is a rare problem due to a high TSH would show up clinically as an overactive thyroid and low TSH would show up as an underactive thyroid. Also when there are abnormal levels of TSH, the right diagnosis is made by measuring free T3 and free T4 levels.

What causes Fatigue?

Fatigue is typically caused when there are changes in the function of the thyroid. As we mentioned in the ‘cruise control’ example above, a thyroid that’s under active generally results in a decrease in bodily activity, including the brain which would rather sleep.

Energy is increased initially when the thyroid is overactive but during the process, the energy that is wasted decreases the total energy stores in the body, including protein loss. This therefore eventually causes fatigue and loss of stamina and strength.

To help fatigue, if a person takes too much thyroid hormone it may initially help, but the fatigue usually returns. If too much thyroid hormone is taken, this can result in osteoporosis (a loss of bone mass) and problems of the hear, such as irregular rhythms.

What causes Weight Gain?

If the function of the thyroid is decreased, this results in the energy consumption of the body to be decreased and therefore, more energy is available to be readily stored. An underactive thyroid typically causes weight gain, although there are many other causes for weight gain. A decrease in thyroid function results in a decrease in the consumption of energy and as a result more energy is available to be stored. Weight gain is, therefore, typical of an underactive thyroid.

If a person loses the mechanism for wasting extra calories, they start to put on weight. Any extra calories that are consumed, however small, get stored and therefore increase a person’s weight.

Those that are overweight often eat less but still gain weight because they can’t use up the extra calories. This is due to an underactive thyroid.

To use up extra calories and lose weight by taking thyroid hormone will result in weight loss due to protein loss, osteoporosis and problems with the heart. The weight increases again when the thyroid hormone is stopped or reduced.

Some people, who have had an over active thyroid (hyperthyroid) and have been given treatment to bring their thyroid levels back to normal, have more difficulty keeping their weight down now as they did even before they had a thyroid problem.

The explanation may be that a person’s ability to use up extra calories may be impaired if too much thyroid hormone is given for a time. And even though the thyroid levels are normal the person’s weight increases. Due to this and the side effects of taking too much thyroid hormone, losing weight by taking in thyroid hormone is not a good way to lose weight.

Lifestyle changes by eating better and exercising more is the safest approach. Controlling weight after having an over active thyroid can seem more difficult, but it is still quite possible to reach your goal weight.

Am I so tired and can't lose weight all because of my thyroid?

Mrs Wallis is tired for a number of reasons. Having a fulltime job that makes her responsible for primary school children would be enough to make anyone tired. Because of her family history and although she did not have other symptoms of an underactive thyroid, she still made some lifestyle changes that helped her keep her energy levels up and reduce her feelings of fatigue.

Mr Thompson was putting on weight after being medically treated for his overactive thyroid. He had more difficulty keeping his weight down even though his thyroid levels were back to normal. If he takes more thyroid hormone, this might help him lose the weight but it will mostly be protein and he risks heart problems and osteoporosis. Also, it will be even more difficult for him to lose weight if he takes too much thyroid hormone.

Therefore, with a Healthy Eating Plan working with the cause of fatigue and weight gain and getting the thyroid function back to normal, you can be happy in the knowledge that your cruise control is working at it’s best.

© Copyright 2003 Lifetime Nutrition Pty Ltd. Reprinted from Thyrobulletin, Vol. 19, No. 3, 1998.

Thyroid Function Quiz

• Do you have problems losing weight?
• Do you regularly feel tired in the middle of the day or after work?
• Do you experience occasional mood swings or depression?
• Do you occasionally have cold hands and feet?

If you answered yes to any of these questions, then you may have impaired thyroid function and require Donvale Dietetics Specialist Dietetic Assesment.