An overactive thyroid (hyperthyroidism) means too much thyroid hormone (thyroxine) is produced. Grave's disease is the commonest cause, accounting for 75 per cent of cases. It is a disease of the immune system that triggers excessive production of thyroxine, sometimes causing a swelling (goitre) in your neck and eye problems.
Thyroid nodules are the other main cause of hyperthyroidism. These non-cancerous lumps contain abnormal thyroid tissue. Medication for an irregular heartbeat (amiodarone) and mental health drug lithium can also cause the condition.
An underactive thyroid (hypothyroidism) is when your thyroid gland doesn't produce enough thyroxine hormone, causing many of your body’s functions to slow down. The commonest cause is an autoimmune disease called autoimmune thyroiditis, when your body makes antibodies which attack your thyroid gland.
Thyroid eye disease makes the soft tissue in your eye socket swell, pushing your eyeball forward. It is normally linked with an overactive thyroid gland.
A goitre is a swollen thyroid gland that causes a lump in the front of your neck. It can be caused by hyperthyroidism, hormone changes (especially menopause), thyroid cancer or lack of iodine in your diet.
Thyroid cancer is two to three times more common in women and develops when cells in your thyroid grow uncontrollably and produce a lump.
An overactive thyroid can cause many symptoms, but you’ll probably just get two or three. These include: feeling restless, nervous, irritable and emotional; insomnia; tremor in your hands; losing weight despite increased appetite; sweating and sensitivity to heat; diarrhoea; shortness of breath; swelling in your neck and loss of libido.
An underactive thyroid slows your body down. Common signs are feeling tired, gaining weight, constipation, feeling cold, poor memory and concentration, dry hair and skin and irregular periods.
Signs of thyroid eye disease include aching behind your eyes; red and irritated eyes; dry eyes; ‘bulging’ eyes; double vision and sensitivity to light.
A thyroid function blood test is the starting point for diagnosing a thyroid disorder and can be ordered by your GP. This test measures the level of thyroid-stimulating hormone (TSH), responsible for stimulating the gland to produce thyroxine.
If you have hyperthyroidism, there is a low level of TSH as too much thyroxine in your blood means less TSH is released. If a raised TSH level is found, you’re likely to have an underactive thyroid as when thyroxine level is low, your thyroid produces more TSH. Levels of thyroxine are also measured.
Who gets thyroid conditions?
Women are 10 times more likely to develop hyperthyroidism than men. Half of people affected by Grave's disease have a family history. Overactive thyroid affects one in 2,000 people a year. It’s more common in smokers, and people who are iodine deficient are also at risk.
Around 15 in 1,000 women and 1 in 1,000 men develop an underactive thyroid, most commonly around age 60. Babies are sometimes born with an underactive thyroid and all are screened at birth for this.
Thyroid eye disease is less common, with 16 women and three men per 100,000 affected. It's more common in smokers and most also have hyperthyroidism.
Anti-thyroid drugs are used to reduce production of thyroid hormones in hyperthyroidism. Carbimazole or methimazole are normally prescribed and take 4 to 8 weeks to work, and will be continued for 12 to 18 months.
Radioactive iodine treatment may be given to destroy some of the excess thyroid tissue to reduce the amount of thyroxine produced. Surgery is occasionally done if you have a large goitre causing problems.
Underactive thyroid is treated with thyroxine (Levothyroxine) tablets, which boosts thyroxine levels. Treatment is for life, so you must take the pill every day.
Thyroid eye disease is normally treated by an eye specialist. Artificial tears help with dry eyes, and immuno suppressants help control the condition.
Important vitamins for healthy thyroid function include B vitamins, especially vitamin B6 which is essential for utilising iodine.