Most people could name at least one friend or acquaintance who has suffered from -"thyroid trouble". However, although it is a relatively common condition, especially among women, most of us know little about it.

Why is there such a degree of ignorance when women are so well informed these days about other medical matters, such as heart disease and breast cancer? One reason is that, although thyroid disorders can become very serious, they are largely responsive to treatment and rarely prove fatal, another is that when the thyroid ceases to function properly, the symptoms can take a wide variety of forms, many of which can be confused with the effects of other common illnesses. The thyroid is a gland whose job is to produce certain vital hormones. It is situated in the front of the neck, but it cannot normally be seen or felt unless it becomes swollen. The action of the thyroid is very complex, but one factor which is vital is the presence in the diet in fish and dairy products, for example - of iodine, which is essential in the formation of thyroid hormones. At times when the body needs high levels of iodine, such as during puberty and pregnancy, the working of the thyroid can be affected.

Most thyroid disorders, however, cannot be set right by changes in diet, since trouble tends to stem not so much from the level of iodine in the body as from the mechanism for absorbing the iodine and turning it into thyroid hormones in the gland. There may be an excess formation of the hormones, or hyperthyroidism, because of either abnormal stimulation from the brain or over-activity on the part of the thyroid itself. Or there may be an inadequate formation of the hormone because of some defect in the gland or lack of stimulation from the brain. This condition is known as hypothyroidism.

The most common symptom of hyperthyroidism is a swelling in the front of the neck, usually called a "goitre". Linked with this may be increased nervousness and irritability. Some people suffer heat intolerance - they sweat easily and demand to have the heating off and the windows open. There may well be some weight loss, and women may find their periods become irregular. Sometimes the eyes become rather prominent and bulging; and, if the disease is not checked, other systems of the body, such as the heart, may become involved, giving rise to palpitations. Hypothyroidism usually results in people feeling increasingly slow, tired and weak. They may find their memories failing; and they may develop an exaggerated dislike of the cold. Their voices can grow husky and hoarse, and their hair can become coarse and thin.

Many of these symptoms, taken on their own, could be caused by other illnesses, or by stress or increasing age. How many people reading this are now wondering if their tiredness or irritability has been caused by thyroid disorder? This is one of the problems of diagnosing thyroid disease. The other is that the symptoms develop gradually. It often takes someone you have not seen for some time to notice the difference and draw your attention to your husky voice or swollen neck. Indeed, it is sometimes left to hairdressers to tell women about the marked change in their hair condition.

"Figures for Britain show that between twenty-two and twenty-nine people in every thousand suffer from overactivity of the thyroid, and that between fifteen and twenty people in every thousand suffer from under-activity . . ."

Figures for Britain show that between two and twenty-nine people in every thousand suffer from over-activity of the thyroid, and that between fifteen and twenty people in every thousand suffer from under-activity. Hyperthyroidism is five times more common, and hypothyroidism over ten times more common, in women than in men.

Where symptoms suggest some disorder, a GP will, if he thinks it necessary, use a blood sample to estimate the level of circulating thyroid hormones. If the results show an abnormally high or low level, further tests are done on the original sample to find the cause of the abnormality. Once the doctor has this detailed information he can discuss the situation with the patient, and embark on a course of treatment.

If the patient is hyperthyroid, there are three possible types of treatment-anti-thyroid drugs, surgery and treatment with radioactive iodine. When antithyroid drugs are given, the patient is treated at an out-patient clinic, but close and regular hospital supervision is kept, to watch for possible side effects. The treatment is likely to continue for one to two years, but sometimes relapses occur and there has to be a re-evaluation of the treatment. Surgical operation, in the form of a partial removal of the thyroid, is an effective method of treatment which does not normally involve being in hospital for more than a week to ten days. The incision is made through the front of the neck and great care is taken to make the cut along the natural crease of the neck, so that after a time the scar ceases to be visible. This is a once-and-for-all treatment, and no medication needs to be taken afterwards, Radioactive iodine treatment is also very effective, but it is not usually given to patients under forty years old. It may also reduce thyroid activity so effectively that the patient actually becomes hypothyroid. Because of this, a lifelong follow up is essential. The treatment of an underactive thyroid is generally simpler. Treatment with thyroid hormones, in the form of tablets, can be prescribed by the patient's GP or the hospital. The dose may later have to be adjusted, and it is important for the patient to realise that the treatment is for life.

Some hospitals may be able to do thyroid scans, which enable them to visualise the gland and understand in more detail why it is not working properly. Only a very small proportion of thyroid sufferers will have such investigations, but it is important to understand that further investigation does not necessarily mean that the condition is more serious simply that more details are required before effective treatment can be started. One fear that patients have, particularly when the thyroid is swollen, is that it is associated with cancer. Like any other organ in the body, the thyroid can be affected by cancer, but fortunately it is rare and can be treated There is certainly no proof that a benign swelling might subsequently become malignant.