Thyroid disease and osteoporosis

What is osteoporosis?

Osteoporosis - literally ‘porous bones’ - is a medical condition whereby your bones become fragile and are more likely to break. The common sites for breakage are the wrist, spine and hip. Although osteoporosis can be treated it is better to prevent it in the first place.

How does osteoporosis occur?

Two types of cells are constantly at work in your bones to allow your skeleton to grow and repair any damage such as fractures. ‘Osteoclasts’ break down the bone while ‘osteoblasts’ build it up again. Each ‘turnover’ cycle normally takes 200 days.

Many factors influence this process of bone replacement, including hormones, the amount of exercise you take and the amount of vitamin D and calcium in your diet.

The rate at which the bone replacement occurs is normally in balance. If more bone is lost than is replaced, your bones become less dense and you may develop osteoporosis. If you develop osteoporosis your bones can break more easily.

Who is at risk for osteoporosis?

All men and women are at risk for osteoporosis - everyone starts to lose some bone density from the age of 35 years and this is just a normal part of ageing. It is more common, however, in older women after the menopause, as they stop producing oestrogen, a hormone that protects the bones. After the menopause bone can be lost more rapidly over the next five to ten years.

Factors that increase the risk of osteoporotic fractures include:

• Personal history of a broken bone, especially a fragility fracture either occurring spontaneously, or as a result of low trauma such as a minor fall

• Family history of osteoporosis or low trauma fracture

• Early menopause

• Previous steroid therapy

• Anorexia nervosa

• Low body weight

• Poor diet

• Smoking

• Excessive alcohol intake

• Lack of exercise or mobility

• Prolonged untreated hyperthyroidism

• Prolonged over-treated hypothyroidism

• Other illnesses such as rheumatoid arthritis, coeliac disease, and primary hyperparathyroidism

What is the link between thyroid disease and osteoporosis?

Thyroid hormone affects the rate of bone replacement so plays a crucial role in maintaining healthy bones. Too much thyroid hormone (i.e. thyroxine) in your body speeds the rate at which bone is lost. If this happens too fast the osteoblasts may not be able to replace the bone loss quickly enough. If the thyroxine level in your body stays too high for a long period or the Thyroid-Stimulating Hormone (TSH) level in your body stays too low for a long period, then there is a higher risk of developing osteoporosis. A recent large UK study found no association between a low TSH level and risk of fragility (osteoporotic) fractures. However, medical opinion is still divided on this issue.

Overactive thyroid (hyperthyroidism)

If you have hyperthyroidism, the first step is to treat the overactivity. Once the level of thyroid hormone in your body has been reduced to a normal level the rate of bone loss will no longer be so rapid and the bone strength may improve. Some people, however, will have or continue to have bone loss, with or without thyroid disease. Postmenopausal women are at particularly high risk of this. If you have had a long period of untreated hyperthyroidism and have other risk factors for osteoporosis and bone fractures, a bone density scan two to three years after you start thyroid treatment will help assess your risk. If a bone density scan shows osteoporosis then this can be treated with osteoporosis medication.

Find more information on living with thyroid disorders. Many patients also find our network of volunteer telephone contacts and local support groups a valuable resource.

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