The term goitre refers to an enlarged, visible thyroid gland. The thyroid gland is a small butterfly-shaped gland in front of the neck. The normal size is about the size of two thumb nails. The thyroid gland secretes thyroid hormones that are vital in converting food into energy and keeping you alive.

The gland takes iodine from the blood to make thyroid hormones. The iodine in the blood comes from the food we eat. The iodine in the food comes from the soil. The soils in upland areas is usually low in iodine because the chemical gets leached from the soil by rain and is taken to the rivers and eventually to the sea. As a result, plants like sea weed and sea food have a lot of iodine.

To ensure that their citizens get enough iodine in the diet, countries usually pass laws to put iodine in the salt. The salt sold in countries that are far from the sea has a higher iodine content than in countries that border the seas or oceans. In Zambia, all the salt sold for human consumption must have a prescribed amount of iodine. It is illegal to sell salt with no iodine in this country.

Goitres are much more common in women than in men. They are also more common in highland regions than in coastal regions. Goitres also seem to run in some families more than in others.

So, why does the thyroid gland enlarge and become a goitre? First, it is important to understand that lack of iodated salt is not the cause of goitre. Iodated salt is the solution to a lack of iodine in the diet.

The commonest reasons for the development of a goitre are:

1. Lack of iodine in the diet. When there is not enough iodine in the blood to make the thyroid hormones, the thyroid enlarges so that it can extract more iodine. If the amount of iodine in the blood from the food – including from iodated salt – becomes normal, then the gland goes back to normal. However, sometimes this signal for the thyroid gland to enlarge develops a life of its own, and the stimulation to enlarge does not stop. This can lead to the development of a very large and sometimes disfiguring goitre. A large goitre can obstruct the gullet as well as the breathing tube called the trachea.
2. The body attacking itself. For reasons that we still do not understand well, the body sometimes attacks the thyroid gland with chemicals — antibodies — produced by the body itself. These antibodies normally attack foreign substances like bacterial and viruses. But this system goes rogue and attacks the thyroid gland instead. Similarly, other glands like the pancreas can be attacked leading to diabetes that is found in children, type 1 diabetes. These rogue chemicals can stimulate or switch off the functioning of the thyroid gland. When the gland is stimulated, it enlarges and starts secreting large amounts of the thyroid hormone. This leads to the development of a goitre as well as symptoms of thyroid overactivity. When the gland is switched off, it stops producing hormones and leads to symptoms of thyroid underactivity. In an effort to try and increase thyroid production, the thyroid gland enlarges into a goitre, but this does not solve the problem because the rogue chemicals do not allow the gland to make any more thyroid hormone.
3. Infections. Very rarely, a viral infection can afflict the thyroid gland. This causes the gland to be inflamed and often enlarges.
4. Puberty. In some girls, at the time of puberty, the thyroid gland can enlarge and become visible as a goitre. This usually reverts to normal size within a few months.
5. Pregnancy. In some pregnant women, the thyroid gland can enlarge and become visible as a goitre. This usually reverts to normal size within a few months.
6. Genetics. As mentioned above, the development of a goitre seems to run in families. Usually, this occurs in women
7. Diet. In places where there is low iodine content in the food and there is no iodated salt to compensate for this, certain foods and medicines can lead to the development of a goitre. These foods include those in the cabbage family, cassava, and soya beans. This only happens if there is not enough iodine in the blood from the diet. In Zambia, this occurs in places where the locals use local salt that is not fortified with iodine.
8. Cancer. In a few cases, cancer can develop in the thyroid gland leading to a visible goitre

In the next article, I shall go into details about the symptoms of overactivity and underactivity of the thyroid gland. This overactivity and underactivity can be associated with the presence of goitre. In some instances, the symptoms can be there but without any goitre.