Diseases that are caused by too much or too little hormone are still common. For instance about 700 million people worldwide are estimated to have a goitre, an enlargement of the thyroid gland that is seen as a big lump on the front of the neck. Iodine is essential to the production of the thyroid hormones T4 and T3, but many parts of the world, particularly landlocked mountainous areas like the Alps and regions of China, have soil which is deficient in iodine.
As a consequence, many people living in iodine-deficient areas have goitre. In Britain, the area around the Peak district was one such affected area and because so many people who lived there had goitre, the condition became known as Derbyshire neck. About 26 million people worldwide have brain damage caused by their thyroid condition, and of these some 6 million are sufficiently mentally handicapped that they are completely dependent on others.
This condition is known as cretinism and symptoms include intellectual impairment, hearing or speech problems, stunted growth and poor movement. This misery is caused by the thyroid gland not working as it should because it is unable to obtain the iodine it needs for proper function. It is completely preventable with iodine supplements. In Britain, most of our table salt is now iodized with potassium iodide, and therefore the deficiency is no longer seen.
Thyroid problems can also be made worse by diet. An example is cassava, a staple food in Africa which, if not prepared properly, contains a chemical which blocks uptake of iodine. Soy beans also affect thyroid function, as do vegetables from the cabbage family, like cabbage itself, turnips and broccoli, further reducing what little thyroid hormone there is. The thyroid is rather like an iodine sponge. It will soak up whatever it can get hold of until it can take no more. This is why giving potassium iodide tablets to people in the immediate aftermath of a nuclear explosion will prevent their bodies from taking up radioactive iodine because the thyroid will have been so flooded by iodine that it cannot absorb any more.
Written texts make clear that in the Middle Ages the Chinese knew how to treat goitre and prescribed seaweed (which, like any food from the sea or grown by the sea, contains large quantities of iodine). In the fourteenth century, Chinese physicians recommended treating goitre with fifty desiccated pigs’ thyroids, ground up in a glass of wine. Today there is still debate as to whether or not desiccated whole thyroid extract is better than synthetic thyroid hormone.