Find out about your thyroid gland
Women are ten times more likely to suffer from thyroid disease than men. The thyroid is a butterfly-shaped gland situated in the neck. It produces the hormones thyroxine (T4) and tri-iodothyronine (T3). Thyroxine is converted by the tissues and organs that need it into the active hormone tri-iodothyronine. In healthy people, the production of these hormones is regulated by the secretion of thyroid stimulating hormone (TSH) from the pituitary gland in the brain. Thyroid hormones regulate the metabolism of the body’s cells.
There are two main causes of thyroid underactivity (hypothyroidism) in the UK:
- autoimmune thyroid disease
- a side effect of treatment for an overactive thyroid or thyroid cancer.
When there is too little thyroid hormone, the body’s metabolism slows down. Symptoms include fatigue, lethargy, weight gain, dry skin and hair, low mood, impaired concentration and memory and constipation. Thyroxine (or levothyroxine) is the thyroid hormone replacement recommended in the British National Formulary. Around 3% of women over 50 are currently treated with thyroxine.
Thyroid overactivity (hyperthyroidism) is less common, affecting around 1.5% of women of this age. There are two main causes of hyperthyroidism in the UK:
- Autoimmune thyroid disease (Graves’ disease) accompanied by the presence of TSH-receptor antibodies in the blood.
- One or more benign (non-cancerous) thyroid nodules which secrete excess thyroid hormone.
When there is too much thyroid hormone, the body’s metabolism speeds up. Symptoms include fatigue, sweating, heat intolerance, weight loss, difficulty sleeping, shaking, palpitations with a fast or irregular heart beat and anxiety. Patients with Graves’ disease may develop eye problems such as grittiness and soreness, protrusion of the eyeballs and rarely, problems with vision. Hyperthyroidism may be managed with a course of antithyroid drugs, radioiodine treatment or thyroid surgery.
Thyroid and the menopause
As some symptoms of thyroid disease can be similar to postmenopausal symptoms, it’s not unusual for them to be incorrectly attributed to the menopause or even put down to stress. To check the diagnosis, a blood test for thyroid function should be performed. Hypothyroidism is usually managed by a GP whereas hyperthyroidism will be managed, at least initially, by an endocrinologist in a specialist thyroid clinic. Borderline results may need to be repeated and monitored for a period of time with specialist advice from an endocrinologist.
HRT and phytoestrogens
Some women who experience severe menopausal symptoms due to oestrogen deficiency may be prescribed HRT. Women who have no pre-existing thyroid disorder and have normal thyroid function usually adapt well to the effects of the HRT and their thyroid function remains normal. However, women with pre-existing hypothyroidism treated with thyroxine, may require an increase in their thyroxine dose after starting HRT. Therefore it is useful for thyroid function tests to be re-checked after starting HRT.
Soy foods are a traditional component of Asian diets but their alleged health benefits have boosted their popularity in recent years and promoted more widespread consumption. Suggested health benefits include alleviation of menopause-related hot flushes and protection against osteoporosis. There are several soybean components that may contribute to the possible health benefits of soy but most attention has focused on the phytoestrogens, leading to the development of phytoestrogen supplements and the fortification of foods with soybean constituents.
Despite the possible benefits, there have been some concerns that soy may adversely affect thyroid function and interfere with the absorption of synthetic thyroid hormone. However there is little evidence that soy foods or phytoestrogen supplements affect thyroid function in people with normal thyroid function. In people with borderline thyroid function and low iodine intake, soy foods may increase the risk of hypothyroidism. Therefore, it’s important for people who regularly consume soy food to ensure their intake of iodine is adequate. There is also evidence to suggest that soy foods may inhibit the absorption of thyroxine and increase the dose of thyroid hormone required by hypothyroid patients.
Women with hypothyroidism who take calcium carbonate supplements should ensure that they don’t take their calcium supplement within four hours of the thyroxine dose. Calcium carbonate may decrease the absorption of thyroxine by nearly a third when these medications are taken at the same time.
Osteoporosis and thyroid
Thyroid hormone plays a key role in maintaining healthy bones. In post menopausal women, hyperthyroidism is a risk factor for sustaining a hip fracture. In part, this is due to the effects of excess thyroid hormones on the cycle of bone production and resorption. Hyperthyroid patients have shorter phases of building bone and longer phases of bone resorption. Hypothyroidism is also associated with an increase in fracture risk. Whether borderline (subclinical) hyperthyroidism is associated with an increased fracture risk remains less certain as there is not sufficient data to draw definite conclusions in all patient groups.
Thyroid disorders may cause similar symptoms to the menopause. HRT and phytoestrogen supplements don’t seem to affect normal thyroid function, but may reduce the absorption of thyroxine medication in those with hypothyroidism.
For more information
Dr Jackie Gilbert is a consultant in endocrinology and general medicine at King’s College Hospital in London. Her special interests are thyroid disorders and reproductive endocrinology. She is the Secretary of the British Thyroid Association
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