Hypothyroidism occurs when the thyroid is unable to produce sucient levels of thyroid hormone, owing to thyroidal dysfunction, insucient stimulation or, in rare cases, where peripheral tissues are resistant 1 . Globally, it is most prevalent in countries where iodine deficiency is common because of low dietary intake, but this is dicult to accurately quantify owing to the differences among aetiological variations 1 . In countries such as the UK, where dietary iodine intake is usually sucient, hypothyroidism affects around 1–2 of the population and is 10 times more common in women than men 1,2 . Incidence rises with advancing age, to more than 5 in patients aged over 60 years and more than 10 in patients aged over 80 years 3 .
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