  |
 |
8. What strategies can women use to optimise bone health at this stage of life?
Med J Aust 2000; 173 Suppl 6 November: S106-S107 Osteoporosis is a condition of impaired skeletal structure that can lead to greater bone fragility and increased risk of fracture. Risk of osteoporotic fracture is best determined by measuring bone mineral density (BMD), with a value below the young normal reference range (T score, -2.5) indicating increased risk.1 It is estimated that about 40% of all postmenopausal women have osteoporosis and more than 40% will suffer a fracture in their lifetime. More than 80% of these fractures occur in women with a BMD T score of less than -2.5. A common perception is that calcium and exercise are largely ineffective after women have passed their peak bone mass. However, exercise and diet are the most important modifiable, non-pharmacological lifestyle factors which can prevent or reduce the rate of bone loss in women aged over 40 years. These lifestyle interventions should be included in all recommendations for treatment and prevention. It is important to stress that it is never too late to prevent bone loss and fracture; indeed, the best data for the efficacy of lifestyle interventions come from studies of elderly women. Calcium intake Many randomised trials in postmenopausal women have shown that calcium supplements are effective in slowing bone loss in elderly women. In a two-year controlled trial, participants were randomly allocated to one of four treatment groups -- placebo, milk powder, calcium tablet, or calcium tablet plus exercise.2 Calcium tablets and milk powder were equally effective in slowing the rate of bone loss at the hip. The extra phosphorus or protein content of milk powder did not have any deleterious effects on the skeleton. Extra exercise improved the bone density at the hip compared with calcium alone. The recommended daily intake of calcium increases from 800mg in premenopausal women to 1000mg in postmenopausal women. National Institutes of Health consensus data have set the recommended level at 1500mg for both elderly men and women.3 Dairy foods are the major sources of calcium in the Australian diet. The preferred source of calcium is calcium-rich foods, and especially dairy products, which provide a readily absorbed source of calcium. Women aged 40 years and over should consume 3-4 serves of low-fat dairy food daily. Other dietary sources of calcium, such as fortified breakfast cereals, canned fish with edible bones and fortified soy products, also make a valuable contribution to dietary calcium intake. Calcium supplements can be used in individuals who can not meet their calcium requirements from food sources alone. Absorption is best from a dose of 500-600mg of calcium once or twice daily with food. As excess salt consumption increases calcium excretion, advice to avoid salty foods and the addition of salt to meals and during cooking is warranted. Although fibre can impair calcium absorption, the effect is quite small and is best overcome by an adequate calcium intake. A deficiency of vitamin D (necessary for calcium absorption) can be a problem in elderly women with low sunlight exposure. If in doubt, determining the level of circulating vitamin D (25 hydroxy-vitamin D) is indicated. Phytoestrogens In recent years phytoestrogens have become a topic of great public and scientific interest. Over $US2.1 billion was spent on alternative health care in the United States in 1997, much of it by perimenopausal or postmenopausal women.4 Currently, the evidence that any phytoestrogen compound can make a real difference in the area of bone loss is inconclusive. There are a variety of problems:
Exercise Exercise can be recommended as a preventive strategy in itself, or in combination with other therapeutic interventions. For exercise to be effective in preventing or slowing bone loss, it must stress the skeleton. Therefore, exercise which is weight-bearing, such as brisk walking, aerobics or tennis, is more effective than exercises where the body weight must be supported, such as cycling or swimming. Progressive resistance strength training has been shown to be effective for increasing bone mass in premenopausal and postmenopausal women.8-14 This response in bone is specific to the site of loading and dependent on the force applied from the weight lifted.14 Strength training is also important for maintaining muscle strength with ageing. It is extremely important that women who undertake strength training are properly supervised to ensure good technique, especially if they have low bone mass. Balance exercises that reduce falls may also be important in the elderly population. Most exercise studies which have shown a significant effect in slowing or preventing bone loss have been achieved by exercising for one hour at least three times a week.
References
Readers may print a single copy of these pages for personal use. No further
reproduction or distribution of the articles
should proceed without the permission of the publisher. For
permission, contact the
Australasian Medical Publishing Company
<URL: http://www.mja.com.au/>
© 2000 Medical Journal of Australia.
|
