Calcium supplements and bone strength

Our bodies use calcium for many reasons, including function of nerves and muscles and blood clotting. If we don’t have enough calcium for these needs we’re in trouble because our bodies will start drawing calcium from our bones. The result: weak, easily broken bones. So it is important we get enough calcium, by eating calcium-rich foods or by taking calcium supplements.

Bone consists mainly of collagen protein fibres, with calcium and phosphate between these fibres to give strength and rigidity. The amount of collagen present, and therefore the amount of bone, depends on the balance between two types of cells - bone forming cells and bone resorbing cells. If our calcium supply is inadequate to meet all the body’s demands our bone resorbing cells will move into action, redistributing calcium from bones to other parts of the body.

Dairy products, including low fat dairy foods that contain good levels of calcium include: milk, cheese, yoghurt and ice cream. In most western countries older people consume 500mg to 1000mg of calcium each day, but research shows that an additional 500mg to 1000mg of calcium daily can slow bone loss significantly. That would require at least four to six servings of calcium-rich foods every day. Many older people may feel uncomfortable eating those quantities and instead prefer to take calcium supplements.

The recommended dosage for older people at risk of osteoporosis is 500mg to 1000mg daily as a supplement. Calcium is available in many forms, and there is some evidence (and some disagreement) that suggests that soluble calcium supplements are more readily absorbed than less soluble salts, such as calcium carbonate. Calcium alone will not completely stop bone loss, but it can slow it down.

Vitamin D supplements and bone strength

Calcium can only be fully absorbed if the body has enough vitamin D. Unlike other vitamins, vitamin D comes not mainly from food; it is made in the skin as a result of direct exposure to sunlight. Many elderly people lack vitamin D because they don’t spend enough time outside in the sun, but fortunately vitamin D can be taken as a supplement. A daily dose of 500-1000 units can be taken as cod liver oil, halibut liver oil or multivitamin tablets. Alternatively, you take a convenient, once-a-month vitamin D tablet of 50,000 units of calciferol.

If you are concerned about vitamin D, ask your doctor for a simple blood test that will measure your levels.

Calcitriol and bone strength

Calcitriol, produced in the kidneys, is the most active naturally occurring form of vitamin D. It regulates the absorption of calcium from the diet. It has been used for the treatment of osteoporosis in a few countries (including Australia and New Zealand).

Small beneficial effects on bone density have been shown in some trials, but these are much less than the effects of hormone replacement therapy or the bisphosphonates. The effects of calcitriol on fracture numbers are unclear, with one trial suggesting that it decreased the number of fractures, while a second trial suggested that fracture numbers actually increased. Since more effective therapies are now available, these are generally preferred.

Bisphosphonate medications and bone strength

Bisphosphonates are phosphate salts that bind to the bone surface and help prevent the activity of bone resorbing cells. Not only do they prevent further bone loss and reduce the number of fractures, but during the first few years of use they can actually increase bone density. Bisphosphonates are the most intensively studied and increasingly used group of treatments for osteoporosis. The cost of some bisphosphonates are subsidised if you have had a low bone density measurement (high T score) or an osteoporotic fracture. Bisphosphonate medicines include:

• Alendronate (Regular oral tablet)
• Etidronate (Regular oral tablet)
• Risedronate (Regular oral tablet)
• Zoledronic acid (Once-yearly intravenous infusion). 

Bisphosphonates are extremely insoluble. When taken orally, the dosing instructions must be followed precisely to ensure that the maximum amount is absorbed.

• Take the dose first thing in the morning with a full glass of water, at least half an hour before eating.
• Water only: the tablets should be taken only with water, as milk, tea, coffee or fruit juice interfere with their absorption.
• Remain upright (sitting or standing) for at least half an hour after taking the tablet. This prevents it sliding back into the oesophagus, where it may cause irritation and heartburn.
• Do not take calcium tablets at the same time of day.

Hormone replacement therapy (HRT) and bone strength

After menopause, all women experience a decline in bone density. This is directly linked to the lower levels of sex hormones produced by the ovaries. Hormone replacement therapy (HRT) - the medical administration of ovarian sex hormones, or similar compounds - can restore a woman’s hormones to pre-menopausal levels.

Oestrogen is the particular hormone that influences bone density. However, most women who take HRT for menopausal symptoms (eg, hot flushes, mood swings) take a combination of oestrogen and progesterone, because the progesterone protects the womb against cancer. If oestrogen is given on its own for many years to women who still have a womb, irregular bleeding can occur and the risk of cancer in the lining of the womb increases. If a woman has had a hysterectomy, she requires only the oestrogen.

If a woman starts HRT at the time of menopause she will prevent postmenopausal bone loss. The risk of fractures developing over the next five to 10 years will also be substantially reduced. More information on HRT.

More recent studies into the balance of risks and benefits with HRT means that HRT is no longer recommended as the first choice treatment for preventing osteoporosis in women. It is more commonly used for a restricted duration to treat symptoms at the time of menopause.

Selective oestrogen receptor modulators (SERMs)

SERMs are fairly new in the treatment for osteoporosis, and have few side effects. In some tissues SERMs mimic the effects of oestrogen, while in other tissues it blocks the actions of oestrogen. This pattern of effects varies from one SERM to another. The SERM raloxifene mimics the effects of oestrogen on bone, however its impact on bone density is not as great as the use of oestrogen itself. It has been shown to reduce the number of fractures in the spinal column, but not necessarily in other parts of the body. Raloxifene also opposes the effects of oestrogen in the breast and breast cancers.

Thiazide diuretics

These have been used for many years for treating high blood pressure or fluid retention. One of their side effects is that they reduce the amount of calcium lost in the urine, resulting in small increases in bone density. They are not effective enough to be used as a sole therapy for osteoporosis, but can be useful when used in conjunction with other medicines.

Calcitonin

Calcitonin, a hormone, is produced by the thyroid gland in the neck. While it reduces the activity of the bone resorbing cells, it is less effective than other treatments, and is not available in New Zealand for use in osteoporosis. Whether it prevents fractures remains controversial. Administration must be by injection or nasal spray, because calcitonin is digested if taken by mouth.

Fluoride

Fluoride salts have been used in the past for treating osteoporosis. Clearly, they can increase bone density, but this is not always paralleled by a reduction in the number of new fractures. Some evidence suggests that higher doses can interfere with the normal structure and strength of bone. As a result of these concerns, fluoride is no longer widely used for osteoporosis, although it is possible that low doses in combination with other treatments, such as hormone replacement therapy, may be effective.

For full information on prescription medicines for osteoporosis, go to www.medsafe.govt.nz

Original material supplied by LivingWith.