Although osteoporosis can affect men, children, and younger women, the highest incidence of the disease is among menopausal women, with one-third of women over 50 and nearly half of those over 70 presenting with symptoms.
Typically strong and resilient in childhood, bones have a dense, ivory-like outer casing or cortex, enclosing an inner core (also known as medulla) of soft marrow filling up the gaps and spaces of the spongy interior. Like all living tissue, bone is able to absorb and utilise a range of proteins and mineral salts from the bloodstream for renewal and repair. Bones generally stop growing in length after the age of 16-18 years, but their density and strength increase until the late 20s.
From the age of around 35 onwards, however, bones become weaker and more fragile due to a loss of mineral salts. This loss intensifies in women as their oestrogen levels fall, peaking at menopause when the production of this hormone from the ovaries ceases altogether.
Thinned-down bones are weaker and more fragile, and the full-blown disease of osteoporosis is responsible for approximately 230 000 fractures yearly in the UK. The most serious of these is a fractured neck or femur (thigh bone) because the long period of immobility during recovery increases the risks of life-threatening conditions such as pneumonia, and DVT (deep vein thrombosis) with subsequent blood clot on the lungs (pulmonary embolism), heart attacks, and strokes. 20-35% of sufferers aged 75-90 years die within 12 months of fracturing their hip joint, around 80% of whom are women.
A dual energy X-ray absorptiometry (DEXA) scan provides the gold standard means of diagnosing osteoporosis.
It expresses bone mineral density in terms of standard deviations (a statistical unit) below that of a young adult reference population.
The unit used is presented as a T-score, and the World Health Organisation (WHO) has established the following guidelines:
- T-score of 1 or greater = normal
- T-score between -1.0 and -2.5 = low bone mass
- T-score of -2.5 or less = osteoporosis
X-rays are helpful for confirming fragility fractures e.g. of the ribs or vertebrae. However, they are relatively insensitive to the identification of early disease, requiring a bone mass loss of at least 30% before picking up diagnostic changes.
The available treatments to reduce risk of fracture act in different ways, either to reduce resorption or to increase formation of bone. The commonest medications used are bisphosphonates, which reduce the resorption of bone as it normally occurs.
The best-known, sodium alendronate, is known to be very effective at preventing bone loss but tends to irritate the food pipe (oesophagus). It is given once a week on an empty stomach, and the patient is advised to remain upright for an hour after taking it. It often causes heartburn, however, and many patients cease to take it for this reason. Other types of bisphosphonates are available.
Hormone Replacement Therapy (HRT), has been shown to reduce the risk of fracture and can be used to prevent or treat osteoporosis in women under the age of 60 who have no contraindications to the use of HRT.
Calcium compounds such as carbonate and citrate, and calcium and vitamin D combinations are also widely prescribed to help improve bones.
These are the building blocks of bone and their effect is best when they are given alongside other treatments such as bisphosphonates and HRT.