There is a wide variation in incidence of thyroid cancer across the world with a low incidence in the UK (circa 1 case per 100,000 of population) to high incidences such as 15 per 100,000 of population in Iceland. These differences are thought to be more due to differences in environment than to hereditary or racial causes - but see next section.
The thyroid is the only gland in the body which concentrates the salt iodine (an integral part of the thyroid hormone molecule) and the relationship between thyroid cancer incidence in iodine rich geographical regions, such as most maritime vicinities, and those with iodine lack (e.g. mountainous terrains of Switzerland – famous in the last century for its goitrous populations) has been studied with interest.
