Hypothyroidism means the thyroid gland is underactive and fails to secrete enough hormones into the bloodstream. Hypothyroidism is the most common thyroid disorder, and it is thought to affect around six to 10 per cent of women. The prevalence rises with age - up to a quarter of women over the age of 65 years may be affected. Men are also affected, but less frequently.
Hypothyroidism can be either primary or secondary. Primary hypothyroidism means that the thyroid gland itself is diseased, while secondary hypothyroidism is caused by problems with the pituitary gland, the brain structure that supervises the thyroid gland. The most common cause of primary hypothyroidism is the autoimmune condition Hashimoto's disease.
Treatment is lifelong hormone replacement with thyroxine tablets.