Of late, do you find yourself becoming very tired or sleepy without any particular reason? Do you feel that you cannot concentrate on your studies or work as well as before? If so, you should have your levels of thyroid hormone checked.

What is the thyroid? Though it is not as well known as the heart or stomach, the thyroid is a very important organ located in the neck, just below your Adam's apple, that produces the thyroid hormone.

This hormone regulates how the body uses and stores energy. Everybody should have a certain, precise level of thyroid hormone in their blood. You become sick if your thyroid gland produces either too much or too little.

When you have too much thyroid hormone (a condition known as hyperthyroidism), you may feel palpitations (quickened heart beat) and may likely have to visit a hospital's emergency room or a cardiologist.

However, when you have too little thyroid hormone (a condition known as hypothyroidism), the symptoms are more vague and not unique to this condition, so many people may not go to see a doctor about them. These symptoms include tiredness, sluggishness, feeling cold, weight gain, dry skin and hair, hair loss, constipation, menstrual irregularities in women, loss of concentration, forgetfulness and depression.

Further complicating things is the fact that many people with hypothyroidism only have one or two of these symptoms.

Consequently, although hypothyroidism is a common and treatable disease, it is often misdiagnosed because its symptoms are nonspecific.

However, untreated hypothyroidism leads to poor mental and physical performance. It usually also causes a high blood-cholesterol level, and may lead to heart disease. Even worse, a life-threatening condition called myxedema coma (loss of consciousness) can develop with severe, untreated hypothyroidism.

For your information, I will now introduce some cases of hypothyroidism that I have come across recently.

A 45-year-old housewife, diagnosed with depression and weight gain, had been taking antidepressants for 10 years. She also often lost concentration during cooking and had burned her hand several times.

The woman came to our clinic a few months ago, complaining of swollen hands. She thought she had rheumatoid arthritis but was found to have hypothyroidism. After treatment with thyroid hormone, she not only recovered from depression but also greatly improved her all-around daily performance.

A 62-year-old woman who had difficulty breathing was admitted to our intensive care unit. She had gained more than 10 kg in the previous two years and her face was puffy. Her voice was low, and she spoke very slowly. We found that a third of her lungs were filled with water. She was also found to have congestive heart failure due to hypothyroidism.

After treatment with thyroid hormone, the woman recovered from heart failure, lost weight and was discharged. Now she lives a normal life without any difficulty breathing, and she speaks clearly in a lighter voice.

A 30-year-old office lady had been worrying about her hair, which had become coarse. She also had to vacuum her bathroom every day because the floor was covered in her lost hair.

The woman went to a dermatologist, but the cause of her hair loss was not found.

Then, her hairdresser suggested that she should see an endocrinologist (hormone specialist), because another customer had the same hair problem and the cause turned out to be thyroid disease.

After treatment with thyroid hormone, the woman's hair returned to normal.

A 76-year-old man became forgetful and was diagnosed with senile dementia a year before. He recently visited my clinic with leg edema, and was found to have hypothyroidism. After treatment with thyroid hormone, his dementia was completely resolved.

Hypothyroidism is a very common disease, but one that is very frequently missed.

If you have any of the above symptoms, it may be wise to see a doctor of internal medicine or an endocrinologist. The doctor will make a blood test to check your thyroid hormone (free T4) and thyroid stimulating hormone (TSH) and may also check your anti-thyroid antibodies to find any cause of hypothyroidism.

Hypothyroidism is treated with thyroid hormone medication. Levothyroxin sodium is the drug of choice. It is a synthetic form of T4 with no side effect at the correct dosage.

If needed, thyroid hormone replacement is good for your life. Have a good-quality life!