Bone supports and protects the tissues of the body and provides a framework enabling body movement. Bone grows during the first two decades of life, with a spurt in adolescence. This is followed by a period of consolidation during which the mass of bone reaches its peak at around the age of 30-35.

The size and shape of each bone is determined by our genes but the potential growth is influenced by the environment, nutrition, physical activity & hormonal factors.

These web pages explain about bone health and disease, and treatments for bone disease.

Remodelling
Bone is a living organ and in the adult body there is a continuous turnover of bone enabling it to repair any damaged micro-architecture and to respond to physical demands being placed upon it such as continual exercise, weight lifting, sports, manual labour etc.

In order for this continual turnover to happen, there is a sequence of bone resorption and bone formation. Osteoclasts or "bone excavating cells" remove pockets of bone as they progress through older mineralised areas. This then creates a cavity ready for new bone formation to occur. Osteoblasts or "bonebuilding cells" then migrate to the area to lay down new bone matrix which goes on to be mineralised. In normal bone this sequence is balanced so that at any one time as bone is removed, bone is also replaced. [For a detailed description of these processes see Mundy G.R. et al., Bone Remodelling, 2003 in Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism. Ed. Favus M.J., Chicago, Illinois. 5th Edition p46-p58.]

Calcium
The adult body contains approximately 1kg of calcium, 99% of which is in the skeleton. Calcium is essential for the proper function of all living cells and the concentration in the blood is precisely regulated by feedback mechanisms acting through the parathyroid glands. Calcium in the blood amounts to approximately 1g.

The chief sources of calcium in the diet are milk and cheese together with some green vegetables, as well as hard water in certain districts. Only a proportion of dietary calcium is absorbed therefore if there is an inadequate daily intake, the required calcium is withdrawn from the bone which as mentioned above maintains 99% of the body store. Calcium is vital to bone health, therefore throughout life we need to maintain a minimum daily intake between 1g and 1.5g of elemental calcium.

Vitamin D
Vitamin D is a fat soluble vitamin which exists in several forms, each with a different activity, some being relatively inactive in the body with limited ability to function as a vitamin. The liver and kidney help to convert vitamin D to its active hormone form. The major biological function of vitamin D is to maintain normal blood levels of calcium and phosphorous. Vitamin D is essential in ensuring the absorption of calcium, helping to form and maintain strong bones.

Vitamin D can be found in some foods but can also be made in the body after exposure to ultraviolet rays from the sun. Dietary sources of vitamin D are largely unpalatable on a daily basis and inadequate as a sole supply, making sunlight the main source.

We cannot ingest the required amount of vitamin D from food alone, it is vital to have sufficient sunlight exposure to ensure adequate levels throughout the year. However, if adequate sunlight is not available, in vulnerable groups supplementation may be necessary as these people may require double that amount (800 international units daily) to achieve adequate vitamin D levels. [Holick M.F. Vitamin D: Photobiology, metabolism, mechanism of action and clinical applications in Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism. Ed. Favus M.J., Chicago, Illinois. 5th Edition p129-p137]

Vitamin D deficiency
When vitamin D deficiency occurs, the process of new bone mineralisation is impaired as calcium transport is reduced. Prolonged vitamin D deficiency, therefore, results in poor bone quality. Reasons for inadequate exposure to sunlight can include the following:

• Those in nursing homes

• Lack of exposure to sun due to sunscreen use

• Some cultural clothing, leaving inadequate areas of skin exposed for vitamin D production

• Ageing itself as older people often tend to stay indoors for longer periods

As we have mentioned, sunlight is the main source of vitamin D but northern countries such as the UK, only have the right level of UV (ultraviolet) sunlight available during summer months (April to September) and around the middle of the day. Sufficient vitamin D is stored from this exposure for the majority of the population to "use" for year round nutrition, but vulnerable groups such as those mentioned above may have inadequate exposure leaving them at risk of vitamin D deficiency all year round.

Vitamin D is important for muscle function as well as bone health and consequently, prolonged deficiency results in weaker muscles making it more difficult to rise from a chair, get out of bed, walk steadily and so on. Since many vulnerable groups have co-existing calcium deficiency due to poor diet, cultural diet (containing little calcium), allergies or a preference not to take dairy produce, the combined results may produce secondary hyperparathyroidism as the parathyroid glands try to correct the situation. Therapeutic levels of combined calcium and vitamin D supplementation can be prescribed to correct this situation.

The elderly generally consume less calcium containing foods such as milk, than other age groups and their main source of vitamin D comes from sunlight. However, as women age, their skin is less able to manufacture vitamin D and their exposure to sun declines as they become less mobile. Therefore if adequate skin exposure is not possible, there may be less vitamin D available to maintain healthy bone for the remainder of the year. If this situation continues, quality of bone deteriorates and bone mass declines leaving fragile bone which is at risk of fracture, particularly hip fracture.

Osteoporosis is a progressive systemic skeletal or bone disorder which is characterised by low bone mass and micro-architectural deterioration of bone tissue with a consequent increase in bone fragility and risk of fracture. All bone elements, cells, bone matrix and mineral are proportionately lost in this disease.

An important effect of osteoporosis is a fracture following a minor event or trauma. However, not all fractures are evident, for instance vertebral fractures and are often only detected on investigation following loss of height some time later. Other common sites of fracture are wrist and hip, which are rarely missed. Osteoporosis can affect all ages, male and female.

Nursing home residents
Nursing /residential home residents over the age of 70 with a low body weight are at high risk of hip fracture. Compounding this may be reduced activity, muscle weakness, reduced exposure to sunlight, use of sunscreen when taken outdoors in summer (which is necessary to protect the skin), extra clothing due to "feeling the cold" and a reduced intake of dairy produce and calcium.

Prolonged bone loss results in weak bones, furthermore, vitamin D deficiency can also result in muscle weakness. It is not surprising therefore, that many older people fall and fracture (break) their hip. It is always better to prevent such a situation but knowing who is at risk of hip fracture is the best way to prevent it happening in the first instance. Older people living independently may also be at risk; to find out more, please read on.

Preventing falls
Simple measures to reduce the potential to fall can be very easily put into place by relatives, friends and health professionals. These might include:

• Ensure adequate light in stairwells and hallways

• Tape down loose rugs and carpets

• Maintaining eyeglass prescriptions

• Taking prescribed medicines according to directions

• Supervised gentle exercise with physiotherapists is important to muscle strength and may be suggested following a fall or as a preventitive measure

Therapeutic levels of calcium plus vitamin D have been shown to significantly reduce the incidence of all fractures, including hip, in both elderly women with a high risk of hip fracture living in institutions and in independently living men and women over age 65.

A large study of white Caucasian females aged 70 and above indicated a reduction in the total number of hip fractures by 43% in 18 months with supplements of 1.2g of elemental calcium and 800 international units vitamin D3.

Bisphosphonates
Bisphosphonates inhibit bone resorption by their effect on osteoclasts and osteoblasts and increase bone mineral density. They are effective in reducing fractures when taken for longer periods of time but great care must be taken in those with acid reflux, indigestion, ulcer and similar conditions.

These products are not well absorbed (less than 1 per cent) and therefore must be taken on an empty stomach, first thing in the morning in the absence of food or drink. Importantly, all osteoporosis therapies for prevention or treatment should begin with adequate calcium and vitamin D nutrition. Of particular importance when receiving bisphosphonate therapy, is to adequately maintain through diet, sunshine or supplementation, both of these nutrients.

If you are prescribed any medication by your doctor, you must advise him of any significant changes in your lifestyle, diet or any other medicines which you may also be taking.

Those women taking hormone replacement therapy (HRT) usually do so for symptomatic relief of vasomotor symptoms such as hot flushes and night sweats.

Selective Estrogen Receptor Modulators or SERMs act by selectively interacting with oestrogen receptors, which occur in many body tissues and by reducing bone resorption. It is also worth noting that they can increase the incidence of hot flushes but may have a protective effect on the breast tissue.

Calcium is vital to bone health and is found mainly in dairy foods. However, there are people, who do not like or cannot tolerate dairy products, making minimum daily calcium intake difficult to achieve. Adequate vitamin D is essential for calcium absorption.

Vitamin D is provided mainly from the action of sunlight on our skin in the summer months. Some vulnerable groups, however, who do not get adequate sunlight, may be at risk of vitamin D deficiency.

Those at risk are older people, those staying mainly indoors due to illness or immobility, those in residential or nursing homes and those wearing cultural dress which may prevent exposure to sunlight. For these people, therapeutic supplementation with calcium and vitamin D may be required.

Osteoporosis is a worldwide health issue, with a high prevalence not only in Western countries but also in Asia and Latin America. It is recognized clinically by characteristic fractures that occur when abnormally fragile bone is subject to relatively mild trauma.

Around 40 percent of all American white women and 13 percent of American white men over 50 years old will experience at least one clinically-apparent fragility fracture in their lifetime.

The Markov model, upon which those estimates are based, predicts that 35 percent of women will sustain a vertebral deformity, 18 percent a hip fracture, and 17 percent a wrist fracture in their lifetimes.

Of various fragility fractures, which represent the major complication of the disease, vertebral and hip fracture are associated with pronounced morbidity and excess mortality rates. Thus the prevention and the treatment of osteoporosis are aimed at reducing substantially this risk of fracture.[For detailed reviews of all aspects of osteoporosis and its treatment see Section VI Metabolic Diseases. 2003 in Primer on Metabolic Bone Diseases and Disorders of Mineral Metabolism. Ed. Favus M.J, Chicago, Illinois. 5th Edition p307-p388.

Bone strength, i.e. resistance to fracture, primarily reflects bone density and bone quality. Bone density is determined by the peak bone mass and the amount of bone loss. Bone quality refers to architecture, turnover, damage accumulation and mineralization. Currently there is no accurate measure of overall bone strength, so bone mineral density is frequently used as a proxy measure.

Most osteoporosis cases are not linked to a specific condition. In these primary osteoporosis cases, predictors of low bone mass include female sex, increased age, estrogen deficiency, white race, low weight, family history of osteoporosis, smoking and history of prior fracture. Although low bone mass is a predictor of future fracture risk, studies indicate that the risk of fracture is often related to the risk of fall.

A large number of medical disorders are associated with osteoporosis and increased fracture risk. Among men, 30 to 60 percent of osteoporosis cases are associated with secondary causes, the most common being hypogonadism, use of glucocorticoids and alcoholism. In peri-menopausal women, more than 50 percent of cases are associated with secondary causes. In post-menopausal women, the prevalence of such causes are much lower, according to a 2001 article in the Journal of the American Medical Association.

Among women, four diagnostic categories based on measurements of bone mass, density, and damage have been proposed for assessment done by DXA (single and dual X-ray absorptiometry).

DXA (single and dual X-ray absorptiometry) is one of the methods used to assess bone mineral content of the entire skeleton and of specific sites, including those which are more vulnerable to fractures. Bone mineral content is the amount of mineral in the specific site scanned, and when divided by the area measured can be used to derive a value for bone mineral density (BMD).

The clinical consequences of osteoporosis are the fractures that arise. Biochemical indices of bone turnover can be divided into two groups: markers of bone resorption and markers of formation. A combined approach with BMD and indices of bone turnover could improve fracture prediction in postmenopausal women.

Calcium: Calcium is an important nutrient in the prevention and treatment of osteoporosis, as it slows the rate of bone loss, especially in elderly women with low calcium intake.

Vitamin D: Vitamin D is also given as treatment for osteoporosis. In a 1996 French study of 3,270 elderly women who lived in care homes and were treated for three years with 1,200 mg of calcium and vitamin D, the probability of hip and non-vertebral fractures was significantly reduced, by 29 percent and 24 percent respectively, compared to those given a placebo.

Estrogen stops bone loss in early, late and elderly postmenopausal women by inhibiting bone resorption, resulting in an increase in bone mineral density over one to three years.

HRT has beneficial non-skeletal effects on hot flushes, sleep, mood and cognitive functions.

Several observational studies have shown a small increase in the risk of breast cancer after ten years of HRT use, however benefits for those with colon cancer have also been reported.

SERMs act as an estrogen agonist or antagonist, depending on the target tissue. They competitively inhibit the action of estrogen on the breast and the endometrium, and act as an estrogen agonist on bone and lipid metabolism. In early postmenopausal women, studies with SERMs have shown that they prevent bone loss at all skeletal sites, reduce markers of bone turnover to premenopausal concentrations, and lower serum cholesterol concentration and its LDL fraction without stimulating the endometrium.

Bisphosphonates are stable analogues of pyrophosphate characterized by a phosphorus-carbon-phosphorus (P-C-P) bond. By substituting hydrogen on the carbon atom, various bisphosphonates have been synthesized, the potency of which depends on the length and the structure of the side chain.

Etidronate, the first bisphosphonate, when administered intermittently, increases the BMD of the spine with a reduction of vertebral fracture rate at two years which, in one of the studies, was no longer significant after three years.

Results of a 1996 study in over two thousand women with osteoporosis and at least one prevalent fracture who were treated with alendronate daily for two years showed a 50 percent reduction of vertebral, wrist and hip fracture compared with those given a placebo. Women with low BMD but without prevalent fracture were given alendronate for five years with the same placebo-controlled design. There was a small but insignificant decrease in the frequency of clinical fractures with alendronate, whereas the frequency of vertebral fracture was significantly reduced by the treatment.

When the analysis was restricted to women with osteoporosis, the reduction of all types of fractures was significant.

The optimum duration of treatment is unknown. One study suggests that seven years of treatment with alendronate is safe, but there might be no further beneficial effect after five years on the basis of BMD and bone turnover markers.

In one study, five milligrams of risedronate per day reduced the incidence of patients with new vertebral fractures by 41 percent over three years, and by 65 percent after the first year in over two thousand women with prevalent fractures.  

Calcitonin is a peptide that reduces bone resorption by direct inhibition of osteoclast activity.

Excess secretion of PTH increases bone resorption and bone loss. By contrast there is multiple evidence in osteoporotic animal models that intermittent PTH injection restores bone strength by stimulation of new bone formation, thickening the cortices and existing trabeculae of the skeleton, and perhaps increasing trabecular numbers and their connectivity.