Hypothyroidism in the UK is most commonly due to an autoimmune condition, Hashimoto's disease or chronic immune thyroiditis, often starting in women in the 30-50 age group. The condition usually, but not always, causes the thyroid to swell, and may initially have hyperthyroid symptoms before settling into hypothyroidism.[^7,11,12]

Diagnosis follows testing for antibodies, increased TSH levels, and low T3 and T4 blood levels. However, the hypothalamus may not be producing sufficient TRH and/or the pituitary is not responding to TRH, which can mean blood tests for TSH, T3 and T4 can be misleading.[¹²]

Other causes include:[^9,11]

·      - genetics: congenital hypothyroidism present from birth, or a polymorphism causing a gene difference that is undetected until adulthood;

·      - reduced ability to convert T4 to T3;

·      - receptor resistance;

·      - dietary deficiencies;

·     - exposure to certain chemicals or foodstuffs;

·     - radiotherapy (with iodine isotopes) or surgery to the thyroid or neck;

·     - excess hyperthyroidism medication, or other drugs;

·     - an inability to absorb or use levothyroxine.

Haemangiomas, benign tumours made of small blood vessels (‘strawberry marks’ on the skin), can secrete D3. Rarely, D3 levels can be so high that circulating thyroid hormones are inactivated faster than they can be produced, causing consumptive hypothyroidism.[^6,13]